diff --git a/backend/src/db/migrate.ts b/backend/src/db/migrate.ts
index 7bb0402..ba6df3a 100644
--- a/backend/src/db/migrate.ts
+++ b/backend/src/db/migrate.ts
@@ -992,6 +992,41 @@ CREATE TABLE IF NOT EXISTS sites (
 -- devices in it. The delete endpoint refuses while devices remain.
 ALTER TABLE devices ADD COLUMN IF NOT EXISTS site_id INTEGER REFERENCES sites(id);
 CREATE INDEX IF NOT EXISTS idx_devices_site ON devices(site_id);
+
+-- Mission 02 (SEC-001): server-side session revocation.
+--
+-- JWTs are stateless by design (no per-request DB write), but logout, a
+-- password change, disabling a compromised account, or an admin "sign this
+-- user out everywhere" action all need existing tokens to stop working
+-- without waiting out the 24h expiry. token_version is the mechanism: every
+-- signed JWT embeds the version current at sign time; requireAuth rejects a
+-- token whose embedded version no longer matches the user's row (see
+-- utils/sessionAuth.ts). Bumping the column is the "revoke" action.
+ALTER TABLE users ADD COLUMN IF NOT EXISTS token_version INTEGER NOT NULL DEFAULT 0;
+-- A deactivated account must stop authenticating immediately, same path as
+-- token_version -- both are checked together in one cached lookup.
+ALTER TABLE users ADD COLUMN IF NOT EXISTS active BOOLEAN NOT NULL DEFAULT true;
+
+-- Mission 02 (SEC-002): explicit user <-> site authorization.
+--
+-- 'admin' is a global role and bypasses this table entirely (see
+-- middleware/site.ts). Every other role must hold an explicit row here for a
+-- site to be visible or writable -- no row means no access, not "unscoped".
+CREATE TABLE IF NOT EXISTS user_sites (
+  user_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+  site_id    INTEGER NOT NULL REFERENCES sites(id) ON DELETE CASCADE,
+  created_at TIMESTAMPTZ DEFAULT NOW(),
+  PRIMARY KEY (user_id, site_id)
+);
+CREATE INDEX IF NOT EXISTS idx_user_sites_site ON user_sites(site_id);
+
+-- Mission 02 (SEC-003): TLS trust-on-first-use pinning for the RouterOS
+-- API-SSL connection (see services/mikrotik/tlsTrust.ts). A device's first
+-- successful connection records the peer certificate's fingerprint; every
+-- later connection must present the same one, or the connection is refused
+-- until an admin explicitly re-trusts it (POST /api/devices/:id/tls/reset).
+ALTER TABLE devices ADD COLUMN IF NOT EXISTS tls_fingerprint VARCHAR(95);
+ALTER TABLE devices ADD COLUMN IF NOT EXISTS tls_mode VARCHAR(20) NOT NULL DEFAULT 'pinned';
 `;
 
 const DEFAULT_SETTINGS = [
@@ -1084,6 +1119,31 @@ export async function runMigrations(): Promise<void> {
       console.log('⚠️  Please change the default password after first login!');
     }
 
+    // user_sites backfill (SEC-002 migration), run exactly once. An existing
+    // install had no concept of per-user site access -- every user could see
+    // every site. Preserve that for accounts that predate this table by
+    // granting every non-admin user access to every site that already exists
+    // at the moment this runs. Gated by a settings flag rather than "has zero
+    // rows" -- a user created *after* the backfill is meant to start with no
+    // site access until explicitly granted, and would otherwise look
+    // identical to a pre-existing, never-backfilled user on every later boot.
+    const backfillFlag = await client.query(
+      `SELECT 1 FROM app_settings WHERE key = 'user_sites_backfilled_v1'`
+    );
+    if (backfillFlag.rows.length === 0) {
+      await client.query(
+        `INSERT INTO user_sites (user_id, site_id)
+         SELECT u.id, s.id FROM users u CROSS JOIN sites s
+         WHERE u.role <> 'admin'
+         ON CONFLICT DO NOTHING`
+      );
+      await client.query(
+        `INSERT INTO app_settings (key, value) VALUES ('user_sites_backfilled_v1', 'true')
+         ON CONFLICT (key) DO NOTHING`
+      );
+      console.log('user_sites backfilled for pre-existing non-admin users');
+    }
+
     console.log('Database migrations completed successfully');
   } finally {
     client.release();
diff --git a/backend/src/index.ts b/backend/src/index.ts
index 804055c..2beeb27 100644
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -28,6 +28,8 @@ import {
 import { netflowCollector } from './services/netflow/NetflowCollector';
 import { verifyToken, type AuthPayload } from './middleware/auth';
 import { rateLimitRedis } from './middleware/rateLimitRedis';
+import { getSessionState } from './utils/sessionAuth';
+import { userCanAccessDevice } from './middleware/site';
 import { initSecrets } from './utils/secrets';
 import { reencryptStaleCredentials } from './db/reencryptCredentials';
 import { reconcileStaleGuards } from './services/changeGuard/ChangeGuard';
@@ -160,11 +162,24 @@ terminalNs.use((socket, next) => {
   if (!token) return next(new Error('No token'));
   try {
     const payload = verifyToken(token);
-    if (!TERMINAL_ROLES.has(payload.role)) {
-      return next(new Error('Console access denied for this role'));
-    }
-    socket.data.user = payload;
-    next();
+    // SEC-001: the terminal namespace authenticates over its own handshake,
+    // outside the HTTP requireAuth pipeline, so it needs its own session
+    // revocation check -- otherwise logout/deactivate/revoke-sessions would
+    // not apply to an already-open or newly-opened console.
+    getSessionState(payload.userId)
+      .then((state) => {
+        if (!state || !state.active || (payload.tokenVersion ?? 0) !== state.tokenVersion) {
+          next(new Error('Session no longer valid'));
+          return;
+        }
+        if (!TERMINAL_ROLES.has(state.role)) {
+          next(new Error('Console access denied for this role'));
+          return;
+        }
+        socket.data.user = { ...payload, role: state.role };
+        next();
+      })
+      .catch(() => next(new Error('Could not verify session')));
   } catch {
     next(new Error('Invalid or expired token'));
   }
@@ -189,6 +204,13 @@ terminalNs.on('connection', (socket) => {
         socket.emit('error', 'Too many terminal sessions started. Please wait a moment and try again.');
         return;
       }
+      // SEC-002: a restricted user can't open a shell on a device outside
+      // their authorized sites just by knowing/guessing its id.
+      if (!(await userCanAccessDevice(user, deviceId))) {
+        socket.emit('error', 'You do not have access to this device');
+        return;
+      }
+
       const device = await queryOne<SshExecDevice>(
         `SELECT id, name, ip_address, ssh_port, ssh_username, ssh_password_encrypted,
                 api_username, api_password_encrypted
diff --git a/backend/src/middleware/__tests__/auditFindings.test.ts b/backend/src/middleware/__tests__/auditFindings.test.ts
index 1c31bc4..9eddb4f 100644
--- a/backend/src/middleware/__tests__/auditFindings.test.ts
+++ b/backend/src/middleware/__tests__/auditFindings.test.ts
@@ -5,33 +5,16 @@
  * asserting an opinion. They are not fixes — see the audit report for
  * classification, impact and recommendation of each finding.
  */
-import { signToken, verifyToken, AuthPayload } from '../auth';
+import { AuthPayload } from '../auth';
 import { resolveSiteId } from '../../utils/siteScope';
 
-// ── SEC-001: JWTs are not invalidated by a password/role change ─────────────
+// ── SEC-001: FIXED in Mission 02 ─────────────────────────────────────────────
 //
-// signToken/verifyToken never consult the database — a JWT is self-contained
-// and valid for the full 24h `expiresIn` window regardless of what happens to
-// the account afterward. There is no token version, jti, or revocation list
-// consulted anywhere in requireAuth (see middleware/auth.ts). This test proves
-// the mechanism: a token minted for a role has no way to be invalidated short
-// of rotating JWT_SECRET (which invalidates every session at once).
-describe('SEC-001: JWT sessions carry no revocation mechanism', () => {
-  it('a token remains valid and keeps its original role after being issued, ' +
-     'with nothing in verifyToken that could observe a later password/role change', () => {
-    const payload: AuthPayload = { userId: 42, username: 'ops', role: 'admin' };
-    const token = signToken(payload);
-
-    // Simulate time passing / the account changing in the DB — verifyToken
-    // takes only the token, so it cannot know about that change.
-    const decoded = verifyToken(token);
-
-    expect(decoded.role).toBe('admin');
-    expect(decoded.userId).toBe(42);
-    // No exp check failure, no DB round-trip: the token is still authoritative
-    // for up to 24h from signing, whatever happened to the account since.
-  });
-});
+// This finding ("a JWT could not be revoked before its 24h expiry") is now
+// covered by dedicated regression tests in middleware/__tests__/auth.test.ts
+// ("SEC-001 regression coverage": revoked-version, deactivated-account, and
+// deleted-user cases), backed by utils/sessionAuth.ts and the users.token_version
+// / users.active columns. See docs/AUDITORIA_BASE_2GT.md for status.
 
 // ── SEC-002: "sites" are a display filter, not an authorization boundary ────
 //
diff --git a/backend/src/middleware/__tests__/auth.test.ts b/backend/src/middleware/__tests__/auth.test.ts
index 9bb8cf1..e88c57b 100644
--- a/backend/src/middleware/__tests__/auth.test.ts
+++ b/backend/src/middleware/__tests__/auth.test.ts
@@ -1,8 +1,14 @@
+jest.mock('../../config/database');
+
 import { Request, Response, NextFunction } from 'express';
 import jwt from 'jsonwebtoken';
 import { signToken, verifyToken, requireAuth, requireAdmin, requireWrite, AuthPayload } from '../auth';
+import { queryOne } from '../../config/database';
+import { _resetSessionCacheForTest } from '../../utils/sessionAuth';
 
-const TEST_PAYLOAD: AuthPayload = { userId: 1, username: 'alice', role: 'admin' };
+const mockedQueryOne = jest.mocked(queryOne);
+
+const TEST_PAYLOAD: AuthPayload = { userId: 1, username: 'alice', role: 'admin', tokenVersion: 0 };
 
 // Minimal Express mock helpers
 function mockReq(authHeader?: string): Request {
@@ -16,6 +22,19 @@ function mockRes() {
   return res;
 }
 
+/** requireAuth resolves its session check asynchronously; wait for `next`/`res.status`. */
+function waitForAuth(req: Request, res: Response, next: jest.Mock): Promise<void> {
+  requireAuth(req, res, next as unknown as NextFunction);
+  return new Promise((resolve) => setImmediate(resolve));
+}
+
+beforeEach(() => {
+  jest.clearAllMocks();
+  _resetSessionCacheForTest();
+  // Default: session is current and active, matching TEST_PAYLOAD.
+  mockedQueryOne.mockResolvedValue({ token_version: 0, active: true, role: 'admin' } as never);
+});
+
 // ── signToken / verifyToken ─────────────────────────────────────────────────
 
 describe('signToken / verifyToken', () => {
@@ -25,6 +44,7 @@ describe('signToken / verifyToken', () => {
     expect(decoded.userId).toBe(TEST_PAYLOAD.userId);
     expect(decoded.username).toBe(TEST_PAYLOAD.username);
     expect(decoded.role).toBe(TEST_PAYLOAD.role);
+    expect(decoded.tokenVersion).toBe(0);
   });
 
   it('throws on an expired token', () => {
@@ -69,16 +89,72 @@ describe('requireAuth', () => {
     expect(next).not.toHaveBeenCalled();
   });
 
-  it('calls next and sets req.user for a valid token', () => {
+  it('calls next and sets req.user for a valid, current-version token', async () => {
     const token = signToken(TEST_PAYLOAD);
     const req = mockReq(`Bearer ${token}`);
     const res = mockRes();
-    const next = jest.fn() as unknown as NextFunction;
-    requireAuth(req, res, next);
+    const next = jest.fn();
+    await waitForAuth(req, res, next);
     expect(next).toHaveBeenCalled();
     expect(req.user?.userId).toBe(TEST_PAYLOAD.userId);
     expect(req.user?.role).toBe('admin');
   });
+
+  // ── SEC-001 regression coverage ───────────────────────────────────────────
+
+  it('rejects a token whose session was revoked (token_version bumped)', async () => {
+    const token = signToken(TEST_PAYLOAD); // signed with tokenVersion: 0
+    mockedQueryOne.mockResolvedValue({ token_version: 1, active: true, role: 'admin' } as never);
+
+    const req = mockReq(`Bearer ${token}`);
+    const res = mockRes();
+    const next = jest.fn();
+    await waitForAuth(req, res, next);
+
+    expect(next).not.toHaveBeenCalled();
+    expect(res.status).toHaveBeenCalledWith(401);
+  });
+
+  it('rejects a token for a deactivated account', async () => {
+    const token = signToken(TEST_PAYLOAD);
+    mockedQueryOne.mockResolvedValue({ token_version: 0, active: false, role: 'admin' } as never);
+
+    const req = mockReq(`Bearer ${token}`);
+    const res = mockRes();
+    const next = jest.fn();
+    await waitForAuth(req, res, next);
+
+    expect(next).not.toHaveBeenCalled();
+    expect(res.status).toHaveBeenCalledWith(401);
+  });
+
+  it('rejects a token for a user that no longer exists', async () => {
+    const token = signToken(TEST_PAYLOAD);
+    mockedQueryOne.mockResolvedValue(null as never);
+
+    const req = mockReq(`Bearer ${token}`);
+    const res = mockRes();
+    const next = jest.fn();
+    await waitForAuth(req, res, next);
+
+    expect(next).not.toHaveBeenCalled();
+    expect(res.status).toHaveBeenCalledWith(401);
+  });
+
+  it('uses the current DB role rather than the one embedded in the token', async () => {
+    // Token was signed while the user was an operator; the account has since
+    // been promoted to admin. The request must see the current role.
+    const staleToken = signToken({ userId: 1, username: 'alice', role: 'operator', tokenVersion: 0 });
+    mockedQueryOne.mockResolvedValue({ token_version: 0, active: true, role: 'admin' } as never);
+
+    const req = mockReq(`Bearer ${staleToken}`);
+    const res = mockRes();
+    const next = jest.fn();
+    await waitForAuth(req, res, next);
+
+    expect(next).toHaveBeenCalled();
+    expect(req.user?.role).toBe('admin');
+  });
 });
 
 // ── requireAdmin ─────────────────────────────────────────────────────────────
diff --git a/backend/src/middleware/__tests__/site.test.ts b/backend/src/middleware/__tests__/site.test.ts
new file mode 100644
index 0000000..b2339ce
--- /dev/null
+++ b/backend/src/middleware/__tests__/site.test.ts
@@ -0,0 +1,128 @@
+jest.mock('../../config/database');
+
+import { Request, Response, NextFunction } from 'express';
+import { query, queryOne } from '../../config/database';
+import {
+  siteContext, enforceSiteAccess, isDeviceAccessible, unauthorizedDeviceIds,
+  invalidateUserSiteCache, deviceIdSiteGuard,
+} from '../site';
+import type { AuthPayload } from '../auth';
+
+const mockedQuery = jest.mocked(query);
+const mockedQueryOne = jest.mocked(queryOne);
+
+function mockReqRes(user: AuthPayload | undefined, siteIdHeader?: string) {
+  const req = {
+    headers: siteIdHeader !== undefined ? { 'x-site-id': siteIdHeader } : {},
+    query: {},
+    user,
+  } as unknown as Request;
+  const res = {} as Response;
+  res.status = jest.fn().mockReturnValue(res);
+  res.json = jest.fn().mockReturnValue(res);
+  return { req, res };
+}
+
+beforeEach(() => {
+  jest.clearAllMocks();
+  invalidateUserSiteCache(1);
+  invalidateUserSiteCache(2);
+});
+
+describe('SEC-002: enforceSiteAccess', () => {
+  it('leaves admins unrestricted (siteScope mirrors the raw request)', async () => {
+    const { req, res } = mockReqRes({ userId: 1, username: 'admin', role: 'admin' }, '5');
+    siteContext(req, res, (() => {}) as NextFunction);
+    const next = jest.fn();
+    await enforceSiteAccess(req, res, next as unknown as NextFunction);
+    expect(next).toHaveBeenCalled();
+    expect(req.siteScope).toBe(5);
+  });
+
+  it('scopes a restricted user with no explicit site to their allowed sites', async () => {
+    mockedQuery.mockResolvedValueOnce([{ site_id: 2 }, { site_id: 3 }] as never);
+    const { req, res } = mockReqRes({ userId: 2, username: 'op', role: 'operator' });
+    siteContext(req, res, (() => {}) as NextFunction);
+    const next = jest.fn();
+    await enforceSiteAccess(req, res, next as unknown as NextFunction);
+    expect(next).toHaveBeenCalled();
+    expect(req.siteScope).toEqual([2, 3]);
+  });
+
+  it('403s a restricted user requesting a site they are not a member of (IDOR)', async () => {
+    mockedQuery.mockResolvedValueOnce([{ site_id: 2 }] as never); // only site 2
+    const { req, res } = mockReqRes({ userId: 2, username: 'op', role: 'operator' }, '99');
+    siteContext(req, res, (() => {}) as NextFunction);
+    const next = jest.fn();
+    await enforceSiteAccess(req, res, next as unknown as NextFunction);
+    expect(next).not.toHaveBeenCalled();
+    expect(res.status).toHaveBeenCalledWith(403);
+  });
+
+  it('allows a restricted user requesting a site they are a member of', async () => {
+    mockedQuery.mockResolvedValueOnce([{ site_id: 2 }] as never);
+    const { req, res } = mockReqRes({ userId: 2, username: 'op', role: 'operator' }, '2');
+    siteContext(req, res, (() => {}) as NextFunction);
+    const next = jest.fn();
+    await enforceSiteAccess(req, res, next as unknown as NextFunction);
+    expect(next).toHaveBeenCalled();
+    expect(req.siteScope).toBe(2);
+  });
+
+  it('scopes a viewer with zero site grants to nothing, not the whole fleet', async () => {
+    mockedQuery.mockResolvedValueOnce([] as never);
+    const { req, res } = mockReqRes({ userId: 2, username: 'v', role: 'viewer' });
+    siteContext(req, res, (() => {}) as NextFunction);
+    const next = jest.fn();
+    await enforceSiteAccess(req, res, next as unknown as NextFunction);
+    expect(next).toHaveBeenCalled();
+    expect(req.siteScope).toEqual([]);
+  });
+});
+
+describe('SEC-002: isDeviceAccessible / deviceIdSiteGuard (cross-site device IDOR)', () => {
+  it('denies a restricted user reaching a device in a site they do not belong to', async () => {
+    const req = { siteScope: [2, 3], user: { userId: 2, role: 'operator' } } as unknown as Request;
+    mockedQueryOne.mockResolvedValueOnce({ site_id: 99 } as never); // device belongs to site 99
+    await expect(isDeviceAccessible(req, 42)).resolves.toBe(false);
+  });
+
+  it('allows a restricted user reaching a device in one of their sites', async () => {
+    const req = { siteScope: [2, 3], user: { userId: 2, role: 'operator' } } as unknown as Request;
+    mockedQueryOne.mockResolvedValueOnce({ site_id: 3 } as never);
+    await expect(isDeviceAccessible(req, 42)).resolves.toBe(true);
+  });
+
+  it('never restricts an admin (siteScope null)', async () => {
+    const req = { siteScope: null, user: { userId: 1, role: 'admin' } } as unknown as Request;
+    await expect(isDeviceAccessible(req, 42)).resolves.toBe(true);
+    expect(mockedQueryOne).not.toHaveBeenCalled();
+  });
+
+  it('deviceIdSiteGuard 403s the request end-to-end for a cross-site device id', async () => {
+    const req = { siteScope: [2] } as unknown as Request;
+    const res = { status: jest.fn().mockReturnThis(), json: jest.fn() } as unknown as Response;
+    const next = jest.fn();
+    mockedQueryOne.mockResolvedValueOnce({ site_id: 7 } as never); // not in [2]
+    await deviceIdSiteGuard(req, res, next as unknown as NextFunction, '42');
+    expect(next).not.toHaveBeenCalled();
+    expect(res.status).toHaveBeenCalledWith(403);
+  });
+});
+
+describe('SEC-002: unauthorizedDeviceIds (bulk operations)', () => {
+  it('flags device ids outside the caller scope', async () => {
+    const req = { siteScope: [2] } as unknown as Request;
+    mockedQuery.mockResolvedValueOnce([
+      { id: 1, site_id: 2 },
+      { id: 2, site_id: 9 },
+    ] as never);
+    await expect(unauthorizedDeviceIds(req, [1, 2])).resolves.toEqual([2]);
+  });
+
+  it('returns an empty list for an unrestricted (admin) scope', async () => {
+    const req = { siteScope: null } as unknown as Request;
+    await expect(unauthorizedDeviceIds(req, [1, 2, 3])).resolves.toEqual([]);
+    expect(mockedQuery).not.toHaveBeenCalled();
+  });
+});
diff --git a/backend/src/middleware/auth.ts b/backend/src/middleware/auth.ts
index b9cc989..9e6d69c 100644
--- a/backend/src/middleware/auth.ts
+++ b/backend/src/middleware/auth.ts
@@ -3,6 +3,7 @@ import jwt from 'jsonwebtoken';
 import { createHash } from 'crypto';
 import { query } from '../config/database';
 import { jwtSigningSecret, jwtVerifierSecrets } from '../utils/secrets';
+import { getSessionState } from '../utils/sessionAuth';
 
 export interface AuthPayload {
   userId: number;
@@ -10,6 +11,13 @@ export interface AuthPayload {
   role: string;
   /** Set when the request authenticated with an API token instead of a session. */
   tokenAuth?: boolean;
+  /**
+   * The user's token_version at the moment this JWT was signed (SEC-001).
+   * Absent on tokens from before this field existed -- those are treated as
+   * version 0, which is also where every account's counter starts, so
+   * pre-existing sessions keep working until the next revoking action.
+   */
+  tokenVersion?: number;
 }
 
 declare global {
@@ -90,6 +98,8 @@ export function requireAuth(req: Request, res: Response, next: NextFunction): vo
   const token = authHeader.slice(7);
 
   if (token.startsWith('mtm_')) {
+    // API tokens are revoked by deleting the row (see routes/automation.ts);
+    // they carry no JWT-style version to check here.
     authenticateApiToken(token)
       .then((payload) => {
         if (!payload) { res.status(401).json({ error: 'Invalid or expired API token' }); return; }
@@ -100,12 +110,41 @@ export function requireAuth(req: Request, res: Response, next: NextFunction): vo
     return;
   }
 
+  let payload: AuthPayload;
   try {
-    req.user = verifyToken(token);
-    next();
+    payload = verifyToken(token);
   } catch {
     res.status(401).json({ error: 'Invalid or expired token' });
+    return;
   }
+
+  // SEC-001: reject a token whose embedded session has since been revoked
+  // (logout-everywhere, password change, TOTP disable, deactivation, or an
+  // admin ending the session) rather than trusting the signature alone until
+  // natural expiry. getSessionState is cached for a few seconds, so this adds
+  // no DB round trip on the common path.
+  getSessionState(payload.userId)
+    .then((state) => {
+      if (!state || !state.active) {
+        res.status(401).json({ error: 'Session no longer valid' });
+        return;
+      }
+      if ((payload.tokenVersion ?? 0) !== state.tokenVersion) {
+        res.status(401).json({ error: 'Session was revoked' });
+        return;
+      }
+      // The role in the DB is authoritative going forward -- a demotion/
+      // promotion takes effect on the next request rather than waiting for
+      // the token to expire, at the same cached-lookup cost as the version
+      // check above.
+      req.user = { ...payload, role: state.role };
+      next();
+    })
+    .catch(() => {
+      // Fail closed: if we can't confirm the session is still valid, don't
+      // authenticate the request.
+      res.status(401).json({ error: 'Could not verify session' });
+    });
 }
 
 export function requireAdmin(req: Request, res: Response, next: NextFunction): void {
diff --git a/backend/src/middleware/site.ts b/backend/src/middleware/site.ts
index 00b23db..2c54b99 100644
--- a/backend/src/middleware/site.ts
+++ b/backend/src/middleware/site.ts
@@ -1,12 +1,20 @@
 import { Request, Response, NextFunction } from 'express';
-import { resolveSiteId } from '../utils/siteScope';
+import { resolveSiteId, SiteScope } from '../utils/siteScope';
+import { queryOne, query } from '../config/database';
 
 declare global {
   // eslint-disable-next-line @typescript-eslint/no-namespace
   namespace Express {
     interface Request {
-      /** Active site, or null for the whole fleet (all-sites view). */
+      /** Raw site id requested via header/query, before authorization. */
       siteId?: number | null;
+      /**
+       * The effective, authorized scope for this request (SEC-002):
+       * `null` = unrestricted (admin/API token), a `number` = one authorized
+       * site, `number[]` = every site a restricted user may see when no
+       * explicit site was requested. Set by enforceSiteAccess.
+       */
+      siteScope?: SiteScope;
     }
   }
 }
@@ -14,9 +22,11 @@ declare global {
 /**
  * Reads the active site from the X-Site-Id header (issue #130).
  *
- * An absent, empty or 'all' header means unscoped. That default is what keeps
- * every pre-existing API consumer -- scripts, API tokens, the docs' curl
- * examples -- behaving exactly as it did before sites existed.
+ * An absent, empty or 'all' header means "no explicit selection". That
+ * default is what keeps every pre-existing API consumer -- scripts, API
+ * tokens, the docs' curl examples -- behaving exactly as it did before sites
+ * existed, *for an admin*. For a restricted user it is narrowed to their
+ * accessible sites by enforceSiteAccess below, not left unscoped.
  *
  * A query-string ?site_id= is also honoured, for links and for anything that
  * cannot set headers.
@@ -28,7 +38,168 @@ export function siteContext(req: Request, _res: Response, next: NextFunction): v
   next();
 }
 
-/** Convenience accessor so routes don't repeat the `?? null`. */
-export function activeSite(req: Request): number | null {
-  return req.siteId ?? null;
+// Cached per user for a few seconds -- same trade-off as sessionAuth's cache:
+// a grant/revoke of site access takes a few seconds to propagate, in exchange
+// for not hitting the DB on every request of every route that scopes by site.
+const SITE_CACHE_TTL_MS = 5_000;
+const siteCache = new Map<number, { ids: number[]; cachedAt: number }>();
+
+async function getUserSiteIds(userId: number): Promise<number[]> {
+  const cached = siteCache.get(userId);
+  if (cached && Date.now() - cached.cachedAt < SITE_CACHE_TTL_MS) return cached.ids;
+  const rows = await query<{ site_id: number }>(`SELECT site_id FROM user_sites WHERE user_id = $1`, [userId]);
+  const ids = rows.map((r) => r.site_id);
+  siteCache.set(userId, { ids, cachedAt: Date.now() });
+  return ids;
+}
+
+/** Test/admin-action seam: force the next read to hit the DB. */
+export function invalidateUserSiteCache(userId: number): void {
+  siteCache.delete(userId);
+}
+
+/**
+ * Same authorization rule as isDeviceAccessible, usable outside an Express
+ * request -- the Socket.IO terminal namespace authenticates over its own
+ * handshake and has no `req` to hang a scope on.
+ */
+export async function userCanAccessDevice(
+  user: { userId: number; role: string; tokenAuth?: boolean }, deviceId: number
+): Promise<boolean> {
+  if (user.role === 'admin' || user.tokenAuth) return true;
+  const device = await queryOne<{ site_id: number | null }>(`SELECT site_id FROM devices WHERE id = $1`, [deviceId]);
+  if (!device || device.site_id === null) return true; // let the caller 404, or unassigned = visible
+  const allowed = await getUserSiteIds(user.userId);
+  return allowed.includes(device.site_id);
+}
+
+/**
+ * Authorize the site requested by siteContext against the authenticated user
+ * (SEC-002). Must run after both requireAuth and siteContext.
+ *
+ *  - admin and API-token callers are unrestricted (role model predates sites;
+ *    scoping tokens is tracked as residual work, see docs/AUDITORIA_BASE_2GT.md).
+ *  - a restricted user requesting a specific site must be a member of it, or
+ *    the request is refused (403) -- this is what closes the IDOR: sending
+ *    X-Site-Id for a site you don't belong to no longer works.
+ *  - a restricted user requesting no specific site ("all") is scoped to every
+ *    site they belong to, not the whole fleet.
+ */
+export async function enforceSiteAccess(req: Request, res: Response, next: NextFunction): Promise<void> {
+  const user = req.user;
+  if (!user) { res.status(401).json({ error: 'No token provided' }); return; }
+
+  if (user.role === 'admin' || user.tokenAuth) {
+    req.siteScope = req.siteId ?? null;
+    next();
+    return;
+  }
+
+  try {
+    const allowed = await getUserSiteIds(user.userId);
+    if (req.siteId !== null && req.siteId !== undefined) {
+      if (!allowed.includes(req.siteId)) {
+        res.status(403).json({ error: 'You do not have access to this site' });
+        return;
+      }
+      req.siteScope = req.siteId;
+    } else {
+      req.siteScope = allowed; // may be [] -- "no access to anything", not "all"
+    }
+    next();
+  } catch (e) {
+    res.status(500).json({ error: `Could not resolve site access: ${(e as Error).message}` });
+  }
+}
+
+/** Convenience accessor so routes don't repeat the optional chaining. */
+export function activeSite(req: Request): SiteScope {
+  return req.siteScope ?? null;
+}
+
+/**
+ * Direct-by-id guard for routes keyed on a specific device (SEC-002).
+ *
+ * Meant to be wired with `router.param('id', ...)` (or called explicitly for
+ * a body/query-supplied deviceId, e.g. bulk commands and the terminal) so a
+ * restricted user can't reach a device outside their sites by simply knowing
+ * or guessing its numeric id -- the classic IDOR this mission calls out.
+ *
+ * Returns true if access is allowed (or the device doesn't exist -- the
+ * handler's own 404 is the right response, not a 403 that would confirm the
+ * id exists in someone else's site).
+ */
+export async function isDeviceAccessible(req: Request, deviceId: number): Promise<boolean> {
+  const scope = activeSite(req);
+  if (scope === null) return true; // unrestricted (admin/token), or explicit single site already checked below
+  const device = await queryOne<{ site_id: number | null }>(`SELECT site_id FROM devices WHERE id = $1`, [deviceId]);
+  if (!device) return true; // let the handler 404
+  if (device.site_id === null) return true; // unassigned devices are visible to everyone (should not occur post-migration)
+  return Array.isArray(scope) ? scope.includes(device.site_id) : scope === device.site_id;
+}
+
+/**
+ * Express `router.param('id', ...)` handler that 403s a request for a device
+ * id outside the caller's authorized sites. Mount with:
+ *   router.param('id', deviceIdSiteGuard);
+ * on any router whose `:id` is a device id.
+ */
+export async function deviceIdSiteGuard(
+  req: Request, res: Response, next: NextFunction, idParam: string
+): Promise<void> {
+  const id = parseInt(idParam, 10);
+  if (Number.isNaN(id)) { next(); return; } // let the handler reject the malformed id
+  try {
+    if (!(await isDeviceAccessible(req, id))) {
+      res.status(403).json({ error: 'You do not have access to this device' });
+      return;
+    }
+    next();
+  } catch (e) {
+    res.status(500).json({ error: `Could not resolve device access: ${(e as Error).message}` });
+  }
+}
+
+/**
+ * Bulk-operation guard (SEC-002): given a list of device ids supplied in a
+ * request body (commands, bulk backup/sync, the terminal's single deviceId),
+ * returns the subset the caller is NOT authorized for. An empty result means
+ * every id is in scope. Used where router.param can't help because the ids
+ * don't come from the URL.
+ */
+export async function unauthorizedDeviceIds(req: Request, deviceIds: number[]): Promise<number[]> {
+  const scope = activeSite(req);
+  if (scope === null || deviceIds.length === 0) return [];
+  const rows = await query<{ id: number; site_id: number | null }>(
+    `SELECT id, site_id FROM devices WHERE id = ANY($1::int[])`, [deviceIds]
+  );
+  const allowed = new Set(Array.isArray(scope) ? scope : [scope]);
+  return rows.filter((r) => r.site_id !== null && !allowed.has(r.site_id)).map((r) => r.id);
+}
+
+/**
+ * Same idea as deviceIdSiteGuard, for a route param that identifies a *row*
+ * belonging to a device rather than the device itself (a backup, a config
+ * snapshot, a command run...). `resolveDeviceId` looks up that row's owning
+ * device id; returning null (row not found) lets the handler's own 404 win,
+ * same reasoning as isDeviceAccessible.
+ */
+export function ownedByDeviceSiteGuard(
+  resolveDeviceId: (rowId: number) => Promise<number | null>
+): (req: Request, res: Response, next: NextFunction, idParam: string) => Promise<void> {
+  return async (req, res, next, idParam) => {
+    const rowId = parseInt(idParam, 10);
+    if (Number.isNaN(rowId)) { next(); return; }
+    try {
+      const deviceId = await resolveDeviceId(rowId);
+      if (deviceId === null) { next(); return; } // handler will 404
+      if (!(await isDeviceAccessible(req, deviceId))) {
+        res.status(403).json({ error: 'You do not have access to this resource' });
+        return;
+      }
+      next();
+    } catch (e) {
+      res.status(500).json({ error: `Could not resolve site access: ${(e as Error).message}` });
+    }
+  };
 }
diff --git a/backend/src/routes/auth.ts b/backend/src/routes/auth.ts
index 4c0e5fe..5731a21 100644
--- a/backend/src/routes/auth.ts
+++ b/backend/src/routes/auth.ts
@@ -7,6 +7,7 @@ import { signToken, signRawToken, verifyRawToken, requireAuth } from '../middlew
 import { getSecretsInfo } from '../utils/secrets';
 import { loginRateLimit, rateLimitRedis } from '../middleware/rateLimitRedis';
 import { validatePassword } from '../utils/passwordPolicy';
+import { bumpTokenVersion } from '../utils/sessionAuth';
 
 const router = Router();
 
@@ -50,9 +51,14 @@ router.post('/login', loginRateLimit(), async (req: Request, res: Response) => {
     password_hash: string;
     role: string;
     totp_enabled: boolean;
-  }>(`SELECT id, username, password_hash, role, totp_enabled FROM users WHERE username = $1`, [username]);
+    active: boolean;
+    token_version: number;
+  }>(`SELECT id, username, password_hash, role, totp_enabled, active, token_version FROM users WHERE username = $1`, [username]);
 
-  if (!user || !(await bcrypt.compare(password, user.password_hash))) {
+  // Same generic error for "no such user", "wrong password" and "deactivated"
+  // -- distinguishing them would leak which usernames exist and which are
+  // disabled.
+  if (!user || !user.active || !(await bcrypt.compare(password, user.password_hash))) {
     return res.status(401).json({ error: 'Invalid credentials' });
   }
 
@@ -61,7 +67,7 @@ router.post('/login', loginRateLimit(), async (req: Request, res: Response) => {
     return res.json({ requires_totp: true, totp_token: totpToken });
   }
 
-  const token = signToken({ userId: user.id, username: user.username, role: user.role });
+  const token = signToken({ userId: user.id, username: user.username, role: user.role, tokenVersion: user.token_version });
   return res.json({ token, user: { id: user.id, username: user.username, role: user.role } });
 });
 
@@ -81,11 +87,14 @@ router.post('/totp/verify', rateLimitRedis({ windowSec: 60, max: 5, keyPrefix: '
     return res.status(401).json({ error: 'Invalid token type' });
   }
 
-  const user = await queryOne<{ id: number; username: string; role: string; totp_secret: string | null; totp_enabled: boolean }>(
-    `SELECT id, username, role, totp_secret, totp_enabled FROM users WHERE id = $1`,
+  const user = await queryOne<{
+    id: number; username: string; role: string; totp_secret: string | null; totp_enabled: boolean;
+    active: boolean; token_version: number;
+  }>(
+    `SELECT id, username, role, totp_secret, totp_enabled, active, token_version FROM users WHERE id = $1`,
     [payload.userId]
   );
-  if (!user || !user.totp_enabled || !user.totp_secret) {
+  if (!user || !user.active || !user.totp_enabled || !user.totp_secret) {
     return res.status(401).json({ error: 'TOTP not configured' });
   }
 
@@ -95,7 +104,7 @@ router.post('/totp/verify', rateLimitRedis({ windowSec: 60, max: 5, keyPrefix: '
     return res.status(401).json({ error: 'Invalid TOTP code' });
   }
 
-  const token = signToken({ userId: user.id, username: user.username, role: user.role });
+  const token = signToken({ userId: user.id, username: user.username, role: user.role, tokenVersion: user.token_version });
   return res.json({ token, user: { id: user.id, username: user.username, role: user.role } });
 });
 
@@ -165,6 +174,8 @@ router.post('/totp/disable', requireAuth, async (req: Request, res: Response) =>
   }
 
   await query(`UPDATE users SET totp_enabled = false, totp_secret = NULL WHERE id = $1`, [req.user!.userId]);
+  // SEC-001: disabling 2FA is a security-relevant auth change; force re-auth.
+  await bumpTokenVersion(req.user!.userId);
   return res.json({ ok: true });
 });
 
@@ -181,8 +192,14 @@ router.get('/me', requireAuth, (req: Request, res: Response) => {
   res.json({ user: req.user });
 });
 
-router.post('/logout', requireAuth, (_req: Request, res: Response) => {
-  // JWT is stateless; client just discards token
+// Logout revokes the session server-side (SEC-001) by bumping token_version,
+// rather than relying on the client to discard the token. This invalidates
+// every token issued for the account, not just the one presented here --
+// there is no per-device/per-tab session identity to revoke selectively, and
+// "sign out everywhere" is an acceptable, documented trade for the added
+// safety (see docs/AUDITORIA_BASE_2GT.md, SEC-001).
+router.post('/logout', requireAuth, async (req: Request, res: Response) => {
+  await bumpTokenVersion(req.user!.userId);
   res.json({ message: 'Logged out' });
 });
 
@@ -207,6 +224,10 @@ router.put('/password', requireAuth, async (req: Request, res: Response) => {
 
   const hash = await bcrypt.hash(newPassword, 12);
   await query(`UPDATE users SET password_hash = $1 WHERE id = $2`, [hash, req.user!.userId]);
+  // SEC-001: a password change is exactly the moment a session might be
+  // compromised -- kill every existing token immediately rather than let
+  // them ride out their 24h expiry.
+  await bumpTokenVersion(req.user!.userId);
   return res.json({ message: 'Password updated' });
 });
 
diff --git a/backend/src/routes/backups.ts b/backend/src/routes/backups.ts
index fa5878f..bb0a764 100644
--- a/backend/src/routes/backups.ts
+++ b/backend/src/routes/backups.ts
@@ -4,11 +4,22 @@ import * as path from 'path';
 import { query, queryOne } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeByDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess, ownedByDeviceSiteGuard } from '../middleware/site';
 import { BackupService } from '../services/BackupService';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
+
+// SEC-002: :id/:fromId/:toId here are backup ids, not device ids -- resolve
+// each to its owning device before letting a handler run.
+const backupSiteGuard = ownedByDeviceSiteGuard(async (backupId) => {
+  const row = await queryOne<{ device_id: number }>(`SELECT device_id FROM backups WHERE id = $1`, [backupId]);
+  return row?.device_id ?? null;
+});
+router.param('id', backupSiteGuard);
+router.param('fromId', backupSiteGuard);
+router.param('toId', backupSiteGuard);
 
 const backupService = new BackupService();
 
diff --git a/backend/src/routes/clients.ts b/backend/src/routes/clients.ts
index 70ae868..8766202 100644
--- a/backend/src/routes/clients.ts
+++ b/backend/src/routes/clients.ts
@@ -4,7 +4,7 @@ import { query } from '../config/database';
 import { logSafe } from '../utils/logSafe';
 import { requireAuth, requireAdmin, requireWrite } from '../middleware/auth';
 import { siteScopeByDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { PollerService } from '../services/PollerService';
 import { getQueryApi, bucket } from '../config/influxdb';
 import { fingerprintClient, DEVICE_CATEGORIES, DeviceCategory } from '../utils/clientFingerprint';
@@ -23,6 +23,7 @@ function withCategory<T extends Record<string, unknown>>(row: T): T & { device_c
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 let pollerService: PollerService | null = null;
 export function setPollerService(p: PollerService): void { pollerService = p; }
diff --git a/backend/src/routes/commands.ts b/backend/src/routes/commands.ts
index f112b96..20ab6a8 100644
--- a/backend/src/routes/commands.ts
+++ b/backend/src/routes/commands.ts
@@ -9,12 +9,13 @@ import { Router } from 'express';
 import type { Request, Response } from 'express';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeByDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess, unauthorizedDeviceIds } from '../middleware/site';
 import { query, queryOne } from '../config/database';
 import { commandRunner } from '../services/CommandRunner';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 /** Commands that change how a device is reached, and so deserve a warning. */
 const RISKY_PATTERNS: { pattern: RegExp; why: string }[] = [
@@ -46,6 +47,10 @@ router.post('/preview', async (req: Request, res: Response) => {
   if (!Array.isArray(device_ids) || device_ids.length === 0) {
     return res.status(400).json({ error: 'device_ids array is required' });
   }
+  const forbidden = await unauthorizedDeviceIds(req, device_ids);
+  if (forbidden.length) {
+    return res.status(403).json({ error: 'One or more devices are outside your authorized sites', device_ids: forbidden });
+  }
 
   const size = Math.max(1, Math.min(50, Number(wave_size) || 1));
   const devices = await query<{ id: number; name: string; ip_address: string; status: string }>(
@@ -85,6 +90,10 @@ router.post('/runs', requireWrite, async (req: Request, res: Response) => {
   if (!Array.isArray(device_ids) || device_ids.length === 0) {
     return res.status(400).json({ error: 'device_ids array is required' });
   }
+  const forbidden = await unauthorizedDeviceIds(req, device_ids);
+  if (forbidden.length) {
+    return res.status(403).json({ error: 'One or more devices are outside your authorized sites', device_ids: forbidden });
+  }
 
   const size = Math.max(1, Math.min(50, Number(wave_size) || 1));
   const run = await queryOne<{ id: number }>(
diff --git a/backend/src/routes/configHistory.ts b/backend/src/routes/configHistory.ts
index ff19476..bc97419 100644
--- a/backend/src/routes/configHistory.ts
+++ b/backend/src/routes/configHistory.ts
@@ -1,11 +1,14 @@
 import { Router, Request, Response } from 'express';
 import { query, queryOne } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
+import { enforceSiteAccess, deviceIdSiteGuard } from '../middleware/site';
 import { BackupService } from '../services/BackupService';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
+router.param('deviceId', deviceIdSiteGuard);
 
 const backupService = new BackupService();
 
diff --git a/backend/src/routes/credentialPresets.ts b/backend/src/routes/credentialPresets.ts
index f73fd9f..ffa7e6b 100644
--- a/backend/src/routes/credentialPresets.ts
+++ b/backend/src/routes/credentialPresets.ts
@@ -3,6 +3,7 @@ import { query, queryOne } from '../config/database';
 import { requireAuth, requireAdmin } from '../middleware/auth';
 import { encrypt } from '../utils/crypto';
 import { rateLimitRedis } from '../middleware/rateLimitRedis';
+import { validateRouterOsUsername } from '../utils/routerOsUsername';
 
 const router = Router();
 router.use(requireAuth);
@@ -106,6 +107,8 @@ router.post('/', requireAdmin, presetMutationLimiter, async (req: Request, res:
       .status(400)
       .json({ error: 'name, api_username, and api_password are required' });
   }
+  const sshUsernameError = validateRouterOsUsername(ssh_username);
+  if (sshUsernameError) return res.status(400).json({ error: sshUsernameError });
 
   const existing = await queryOne<{ id: number }>(
     `SELECT id FROM credential_presets WHERE name = $1`,
@@ -184,6 +187,8 @@ router.put('/:id', requireAdmin, presetMutationLimiter, async (req: Request, res
     );
     if (clash) return res.status(409).json({ error: 'A preset with this name already exists' });
   }
+  const sshUsernameError = validateRouterOsUsername(ssh_username);
+  if (sshUsernameError) return res.status(400).json({ error: sshUsernameError });
 
   const newApiPass = api_password ? encrypt(api_password) : existing.api_password_encrypted;
   let newSshPass: string | null = existing.ssh_password_encrypted;
diff --git a/backend/src/routes/devices.ts b/backend/src/routes/devices.ts
index 5c5a2bd..48b6b30 100644
--- a/backend/src/routes/devices.ts
+++ b/backend/src/routes/devices.ts
@@ -2,7 +2,8 @@ import { Router, Request, Response } from 'express';
 import { randomUUID } from 'crypto';
 import { Client as SshClient } from 'ssh2';
 import { query, queryOne } from '../config/database';
-import { requireAuth, requireWrite } from '../middleware/auth';
+import { requireAuth, requireWrite, requireAdmin } from '../middleware/auth';
+import { deviceIdSiteGuard } from '../middleware/site';
 import { encrypt, decrypt } from '../utils/crypto';
 import { RouterOSClient } from '../services/mikrotik/RouterOSClient';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
@@ -12,6 +13,7 @@ import { createDeviceFromBody, type CreateDeviceInput, type CreateDeviceContext
 import { parsePort } from '../utils/parsePort';
 import { safeConnectionError } from '../utils/safeClientError';
 import { detectLockoutRisk } from '../utils/firewallSafety';
+import { validateRouterOsUsername } from '../utils/routerOsUsername';
 import { withSafeApply, probeCapability, probeUndoCapability, type GuardDevice } from '../services/changeGuard/ChangeGuard';
 import { captureSnapshot, resolveManagementPath } from '../services/changeGuard/pathModel';
 import { analyzeChange, type PlannedChange } from '../services/changeGuard/analyzeChange';
@@ -22,8 +24,8 @@ import { enqueueBulkAddJob, getBulkAddJobState } from '../services/DeviceBulkAdd
 import { logSafe } from '../utils/logSafe';
 import { DEVICE_BASE_COLUMNS } from '../services/deviceColumns';
 import { buildSegments, summarise, summariseBands } from '../utils/lteDwell';
-import { siteScopeDevices, andSite } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { siteScopeDevices, andSite, singleSiteOrNull } from '../utils/siteScope';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 
 /** Postgres interval text to milliseconds, for the few windows we offer. */
 function intervalToMs(interval: string): number {
@@ -70,6 +72,12 @@ async function loadCredentialPreset(
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
+// SEC-002: every :id in this router is a device id -- refuse it up front if
+// the device belongs to a site the caller isn't authorized for, before any
+// handler runs. Closes the IDOR of reaching another site's device by guessing
+// or enumerating its numeric id.
+router.param('id', deviceIdSiteGuard);
 
 let pollerService: PollerService | null = null;
 export function setPollerService(p: PollerService): void {
@@ -285,7 +293,7 @@ router.post('/', requireWrite, async (req: Request, res: Response) => {
   const result = await createDeviceFromBody(req.body, pollerService, {
     requestingUserRole: req.user?.role,
     // A device added while viewing a site joins that site (issue #130).
-    siteId: activeSite(req),
+    siteId: singleSiteOrNull(activeSite(req)),
   });
   return res.status(result.status).json(result.body);
 });
@@ -316,7 +324,7 @@ router.post('/bulk-add/jobs', requireWrite, async (req: Request, res: Response)
     BULK_ADD_META_TTL_SEC
   );
   await redis.set(`device-bulk-add:${jobId}:results`, '[]', 'EX', BULK_ADD_META_TTL_SEC);
-  await enqueueBulkAddJob(jobId, items as CreateDeviceInput[], activeSite(req));
+  await enqueueBulkAddJob(jobId, items as CreateDeviceInput[], singleSiteOrNull(activeSite(req)));
   return res.status(202).json({ job_id: jobId, total: items.length });
 });
 
@@ -450,6 +458,11 @@ router.put('/:id', requireWrite, async (req: Request, res: Response) => {
   const ssh_username = preset ? preset.ssh_username : req.body.ssh_username;
   const ssh_password = preset ? preset.ssh_password : req.body.ssh_password;
 
+  // SEC-006: reject an unsafe ssh_username before it can ever reach the
+  // RouterOS CLI command SshKeyService builds from it.
+  const sshUsernameError = validateRouterOsUsername(ssh_username);
+  if (sshUsernameError) return res.status(400).json({ error: sshUsernameError });
+
   // If the user is changing the IP (or port / username / password), verify the
   // RouterOS API is still reachable with the new values before persisting —
   // otherwise we could silently brick the device record.
diff --git a/backend/src/routes/events.ts b/backend/src/routes/events.ts
index e5735a3..fb78931 100644
--- a/backend/src/routes/events.ts
+++ b/backend/src/routes/events.ts
@@ -2,10 +2,11 @@ import { Router, Request, Response } from 'express';
 import { query } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeByNullableDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 // GET /api/events
 /**
diff --git a/backend/src/routes/firmware.ts b/backend/src/routes/firmware.ts
index aa9fa7f..3090a27 100644
--- a/backend/src/routes/firmware.ts
+++ b/backend/src/routes/firmware.ts
@@ -2,7 +2,7 @@ import { Router, Request, Response } from 'express';
 import { query, queryOne } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeDevices, siteScopeByDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
 import { firmwareOrchestrator } from '../services/FirmwareOrchestrator';
 import { clampConcurrency, MAX_WAVE_CONCURRENCY } from '../utils/concurrency';
@@ -10,6 +10,7 @@ import { findUpstreamWithinSelection } from '../utils/rolloutTopology';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 // GET /api/firmware/overview — fleet versions + latest rollout
 router.get('/overview', async (req: Request, res: Response) => {
diff --git a/backend/src/routes/metrics.ts b/backend/src/routes/metrics.ts
index f8356b9..f696201 100644
--- a/backend/src/routes/metrics.ts
+++ b/backend/src/routes/metrics.ts
@@ -2,11 +2,13 @@ import { Router, Request, Response } from 'express';
 import { getQueryApi, bucket } from '../config/influxdb';
 import { query } from '../config/database';
 import { requireAuth } from '../middleware/auth';
-import { siteScopeDevices, siteScopeByDevice, siteScopeByNullableDevice, clientSeriesTag } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { siteScopeDevices, siteScopeByDevice, siteScopeByNullableDevice, clientSeriesTag, singleSiteOrNull } from '../utils/siteScope';
+import { activeSite, enforceSiteAccess, deviceIdSiteGuard } from '../middleware/site';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
+router.param('deviceId', deviceIdSiteGuard);
 
 function rangeToFlux(range: string): string {
   const allowed = ['1h', '3h', '6h', '12h', '24h', '7d', '30d'];
@@ -25,7 +27,15 @@ router.get('/clients-over-time', async (req: Request, res: Response) => {
   // the global series there is not a shortcut -- it keeps the chart's full
   // history, which the per-site series only accumulates from the upgrade
   // onward. That covers every single-site install.
-  const siteId = activeSite(req);
+  // clientSeriesTag needs one concrete site id or the true fleet-wide case.
+  // SEC-002: a restricted user viewing several sites at once has neither --
+  // there is no single dedup series for "these particular sites", and
+  // falling back to `_global` would hand them the whole fleet's count. Such a
+  // scope skips the dedup series entirely and goes straight to the per-device
+  // fallback below, filtered to exactly the devices they may see.
+  const scope = activeSite(req);
+  const siteId = singleSiteOrNull(scope);
+  const restrictedToMultipleSites = Array.isArray(scope);
   let seriesTag = '_global';
   if (siteId !== null) {
     const counts = await query<{ in_site: number; total: number }>(
@@ -40,29 +50,31 @@ router.get('/clients-over-time', async (req: Request, res: Response) => {
 
   // Use the global deduplicated metric (_global tag) written by DeviceCollector.
   // This avoids double-counting clients seen by multiple devices simultaneously.
-  const fluxQuery = `
-    from(bucket: "${bucket}")
-      |> range(start: -${range})
-      |> filter(fn: (r) => r._measurement == "client_counts")
-      |> filter(fn: (r) => r._field == "total_clients")
-      |> filter(fn: (r) => r.device_id == "${seriesTag}")
-      |> aggregateWindow(every: 5m, fn: last, createEmpty: false)
-      |> yield(name: "clients_over_time")
-  `;
-
   const rawPoints: { time: string; value: number }[] = [];
-  try {
-    await queryApi.collectRows(fluxQuery, (row, tableMeta) => {
-      const time = tableMeta.get(row, '_time') as string;
-      const value = tableMeta.get(row, '_value') as number;
-      rawPoints.push({ time, value: Math.round(value) });
-    });
-  } catch {
-    // InfluxDB might not have data yet
+  if (!restrictedToMultipleSites) {
+    const fluxQuery = `
+      from(bucket: "${bucket}")
+        |> range(start: -${range})
+        |> filter(fn: (r) => r._measurement == "client_counts")
+        |> filter(fn: (r) => r._field == "total_clients")
+        |> filter(fn: (r) => r.device_id == "${seriesTag}")
+        |> aggregateWindow(every: 5m, fn: last, createEmpty: false)
+        |> yield(name: "clients_over_time")
+    `;
+    try {
+      await queryApi.collectRows(fluxQuery, (row, tableMeta) => {
+        const time = tableMeta.get(row, '_time') as string;
+        const value = tableMeta.get(row, '_value') as number;
+        rawPoints.push({ time, value: Math.round(value) });
+      });
+    } catch {
+      // InfluxDB might not have data yet
+    }
   }
 
   // If no deduplicated series exists yet (first run, or a site whose history
-  // predates the per-site series), fall back to max across real devices. max()
+  // predates the per-site series), or the caller is scoped to several sites
+  // at once, fall back to max across the exact devices they may see. max()
   // is better than sum() since the device with the most clients is the gateway
   // that sees everyone — summing would double-count clients visible from
   // multiple devices.
@@ -72,12 +84,16 @@ router.get('/clients-over-time', async (req: Request, res: Response) => {
     // it matters: without it the fleet-wide fallback would fold the per-site
     // totals back in and count everyone twice.
     let deviceFilter: string | null = `|> filter(fn: (r) => not (r.device_id =~ /^_/))`;
-    if (siteId !== null) {
-      const ids = await query<{ id: number }>(
-        `SELECT id FROM devices WHERE site_id = $1`, [siteId]
-      );
-      // An empty site has no series to fall back to, and must show an empty
-      // chart rather than the fleet's (issue #130).
+    if (scope !== null) {
+      const scopePredicate = Array.isArray(scope) ? scope : [scope];
+      const ids = scopePredicate.length
+        ? await query<{ id: number }>(
+            `SELECT id FROM devices WHERE site_id = ANY($1::int[])`, [scopePredicate]
+          )
+        : [];
+      // An empty site (or a viewer authorized for zero sites) has no series
+      // to fall back to, and must show an empty chart rather than the fleet's
+      // (issue #130 / SEC-002).
       deviceFilter = ids.length
         ? `|> filter(fn: (r) => ${ids.map((d) => `r.device_id == "${d.id}"`).join(' or ')})`
         : null;
diff --git a/backend/src/routes/networkServices.ts b/backend/src/routes/networkServices.ts
index f1170bf..f892d4b 100644
--- a/backend/src/routes/networkServices.ts
+++ b/backend/src/routes/networkServices.ts
@@ -2,12 +2,13 @@ import { Router, Request, Response } from 'express';
 import { query } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeDevices } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
 import { netflowCollector } from '../services/netflow/NetflowCollector';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 // ─── Helper ───────────────────────────────────────────────────────────────────
 
diff --git a/backend/src/routes/oidc.ts b/backend/src/routes/oidc.ts
index 179dec2..e4fc580 100644
--- a/backend/src/routes/oidc.ts
+++ b/backend/src/routes/oidc.ts
@@ -10,6 +10,7 @@
 import { Router, Request, Response } from 'express';
 import { Issuer } from 'openid-client';
 import { requireAuth, requireAdmin, signToken } from '../middleware/auth';
+import { queryOne } from '../config/database';
 import { rateLimitRedis } from '../middleware/rateLimitRedis';
 import {
   loadOidcConfig, saveOidcConfig, maskedConfig, APP_ROLES, type AppRole, type OidcConfig,
@@ -65,7 +66,14 @@ router.get(
       const params = req.query as Record<string, string>;
       if (params.error) throw new Error(params.error_description || params.error);
       const { user, returnTo } = await completeLogin(params);
-      const token = signToken({ userId: user.id, username: user.username, role: user.role });
+      // SEC-001: SSO users go through the same revocable-session mechanism as
+      // local accounts -- embed the current token_version so a "revoke
+      // sessions" action or deactivation applies to them too.
+      const current = await queryOne<{ token_version: number; active: boolean }>(
+        `SELECT token_version, active FROM users WHERE id = $1`, [user.id]
+      );
+      if (!current || !current.active) throw new Error('Account is deactivated');
+      const token = signToken({ userId: user.id, username: user.username, role: user.role, tokenVersion: current.token_version });
       const dest = safeReturnTo(returnTo);
       // Hand the token to the SPA via fragment (never sent to the server/logs).
       res.redirect(`/auth/callback#token=${encodeURIComponent(token)}&returnTo=${encodeURIComponent(dest)}`);
diff --git a/backend/src/routes/operations.ts b/backend/src/routes/operations.ts
index 3a769f5..03559e6 100644
--- a/backend/src/routes/operations.ts
+++ b/backend/src/routes/operations.ts
@@ -2,13 +2,14 @@ import { Router, Request, Response } from 'express';
 import { query } from '../config/database';
 import { getQueryApi } from '../config/influxdb';
 import { requireAuth, requireWrite } from '../middleware/auth';
-import { siteScopeDevices, siteScopeByDevice, siteScopeByNullableDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { siteScopeDevices, siteScopeByDevice, siteScopeByNullableDevice, singleSiteOrNull, SiteScope } from '../utils/siteScope';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
 import { BackupService, BackupDevice } from '../services/BackupService';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 const backupService = new BackupService();
 
@@ -454,7 +455,7 @@ async function influxGroupValues(flux: string): Promise<Map<string, number>> {
   return out;
 }
 
-async function detectAnomalies(siteId: number | null): Promise<AttentionItem[]> {
+async function detectAnomalies(siteId: SiteScope): Promise<AttentionItem[]> {
   const items: AttentionItem[] = [];
   const hour = new Date().getUTCHours();
   const nameById = new Map<string, { id: number; name: string }>();
@@ -556,7 +557,7 @@ async function detectAnomalies(siteId: number | null): Promise<AttentionItem[]>
 // who did what to the install -- they carry no device and so belong to no site,
 // and repeating "admin changed a setting" into every site would misattribute it.
 // Device-scoped history (config changes, events) is filtered normally.
-async function buildActivity(siteId: number | null) {
+async function buildActivity(siteId: SiteScope) {
   const cfgFilter = siteScopeByDevice(siteId, 'dc.device_id');
   const evtFilter = siteScopeByNullableDevice(siteId, 'e.device_id');
   const [configs, audits, events] = await Promise.all([
diff --git a/backend/src/routes/routers.ts b/backend/src/routes/routers.ts
index 0221aec..f255356 100644
--- a/backend/src/routes/routers.ts
+++ b/backend/src/routes/routers.ts
@@ -2,11 +2,12 @@ import { Router, Request, Response } from 'express';
 import { query } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeDevices } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 // GET /api/routers/lldp — LLDP enabled/disabled status per online router
 router.get('/lldp', async (req: Request, res: Response) => {
diff --git a/backend/src/routes/search.ts b/backend/src/routes/search.ts
index d5b6941..db5bde3 100644
--- a/backend/src/routes/search.ts
+++ b/backend/src/routes/search.ts
@@ -2,10 +2,11 @@ import { Router, Request, Response } from 'express';
 import { query } from '../config/database';
 import { requireAuth } from '../middleware/auth';
 import { siteScopeDevices, siteScopeByNullableDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 // GET /api/search?q=<term>
 router.get('/', async (req: Request, res: Response) => {
diff --git a/backend/src/routes/settings.ts b/backend/src/routes/settings.ts
index b8f9ed1..956edb2 100644
--- a/backend/src/routes/settings.ts
+++ b/backend/src/routes/settings.ts
@@ -5,6 +5,7 @@ import { requireAuth, requireAdmin } from '../middleware/auth';
 import { netflowCollector } from '../services/netflow/NetflowCollector';
 import { validatePassword } from '../utils/passwordPolicy';
 import { OIDC_SETTINGS_KEY } from '../services/oidc/oidcConfig';
+import { bumpTokenVersion } from '../utils/sessionAuth';
 
 const router = Router();
 router.use(requireAuth);
@@ -47,7 +48,7 @@ router.put('/', requireAdmin, async (req: Request, res: Response) => {
 // GET /api/settings/users
 router.get('/users', requireAdmin, async (_req: Request, res: Response) => {
   const users = await query(
-    `SELECT id, username, email, role, auth_provider, created_at FROM users ORDER BY username`
+    `SELECT id, username, email, role, active, auth_provider, created_at FROM users ORDER BY username`
   );
   res.json(users);
 });
@@ -82,10 +83,10 @@ router.post('/users', requireAdmin, async (req: Request, res: Response) => {
   return res.status(201).json(created);
 });
 
-// PUT /api/settings/users/:id - update role and/or reset password
+// PUT /api/settings/users/:id - update role, active flag and/or reset password
 router.put('/users/:id', requireAdmin, async (req: Request, res: Response) => {
   const userId = parseInt(req.params.id);
-  const { role, password } = req.body;
+  const { role, password, active } = req.body as { role?: string; password?: string; active?: boolean };
 
   const existing = await queryOne<{ id: number; role: string }>(
     `SELECT id, role FROM users WHERE id = $1`,
@@ -97,14 +98,29 @@ router.put('/users/:id', requireAdmin, async (req: Request, res: Response) => {
   if (userId === req.user!.userId && role && role !== 'admin') {
     return res.status(400).json({ error: 'Cannot change your own role away from admin' });
   }
+  // Cannot deactivate your own account (mirrors the self-delete guard below;
+  // an admin locking themselves out would need another admin to undo it).
+  if (userId === req.user!.userId && active === false) {
+    return res.status(400).json({ error: 'Cannot deactivate your own account' });
+  }
 
   const validRoles = ['admin', 'operator', 'viewer'];
   if (role && !validRoles.includes(role)) {
     return res.status(400).json({ error: 'Invalid role' });
   }
 
+  // A role change or deactivation is exactly the case SEC-001 exists for:
+  // the account's existing sessions must stop working immediately, not at
+  // their natural 24h expiry.
+  let mustRevoke = false;
+
   if (role) {
     await query(`UPDATE users SET role = $1 WHERE id = $2`, [role, userId]);
+    mustRevoke = true;
+  }
+  if (typeof active === 'boolean') {
+    await query(`UPDATE users SET active = $1 WHERE id = $2`, [active, userId]);
+    if (!active) mustRevoke = true;
   }
   if (password) {
     const pwError = validatePassword(password);
@@ -113,15 +129,28 @@ router.put('/users/:id', requireAdmin, async (req: Request, res: Response) => {
     }
     const hash = await bcrypt.hash(password, 12);
     await query(`UPDATE users SET password_hash = $1 WHERE id = $2`, [hash, userId]);
+    mustRevoke = true;
   }
+  if (mustRevoke) await bumpTokenVersion(userId);
 
   const updated = await queryOne(
-    `SELECT id, username, role, created_at FROM users WHERE id = $1`,
+    `SELECT id, username, role, active, created_at FROM users WHERE id = $1`,
     [userId]
   );
   return res.json(updated);
 });
 
+// POST /api/settings/users/:id/revoke-sessions — end every session for a user
+// right now, without changing their password or role (SEC-001). Useful for
+// "this laptop was stolen" without also forcing an unrelated password reset.
+router.post('/users/:id/revoke-sessions', requireAdmin, async (req: Request, res: Response) => {
+  const userId = parseInt(req.params.id);
+  const existing = await queryOne<{ id: number }>(`SELECT id FROM users WHERE id = $1`, [userId]);
+  if (!existing) return res.status(404).json({ error: 'User not found' });
+  await bumpTokenVersion(userId);
+  return res.json({ message: 'All sessions for this user have been revoked' });
+});
+
 // DELETE /api/settings/users/:id
 router.delete('/users/:id', requireAdmin, async (req: Request, res: Response) => {
   if (parseInt(req.params.id) === req.user!.userId) {
diff --git a/backend/src/routes/sites.ts b/backend/src/routes/sites.ts
index 4ccff37..d84ca16 100644
--- a/backend/src/routes/sites.ts
+++ b/backend/src/routes/sites.ts
@@ -1,6 +1,7 @@
 import { Router, Request, Response } from 'express';
 import { query, queryOne } from '../config/database';
-import { requireAuth, requireWrite } from '../middleware/auth';
+import { requireAuth, requireWrite, requireAdmin } from '../middleware/auth';
+import { invalidateUserSiteCache } from '../middleware/site';
 
 const router = Router();
 router.use(requireAuth);
@@ -36,8 +37,15 @@ function normaliseCoords(lat: unknown, lng: unknown): { lat: number | null; lng:
   return ok ? { lat: latN, lng: lngN } : { lat: null, lng: null };
 }
 
-// GET /api/sites — list with device counts, for the selector and the all-sites table
-router.get('/', async (_req: Request, res: Response) => {
+// GET /api/sites — list with device counts, for the selector and the all-sites table.
+// SEC-002: a restricted (non-admin) caller only sees sites they're a member
+// of -- otherwise every viewer could enumerate every other client's site
+// names regardless of the X-Site-Id enforcement on device data itself.
+router.get('/', async (req: Request, res: Response) => {
+  const restricted = req.user!.role !== 'admin' && !req.user!.tokenAuth;
+  const memberFilter = restricted
+    ? `WHERE s.id IN (SELECT site_id FROM user_sites WHERE user_id = $1)`
+    : '';
   const sites = await query<SiteRow & { device_count: string }>(
     `SELECT s.id, s.name, s.address,
             s.location_lat::float8 AS location_lat,
@@ -47,8 +55,10 @@ router.get('/', async (_req: Request, res: Response) => {
             COUNT(d.id) FILTER (WHERE d.status = 'online')::text AS online_count
      FROM sites s
      LEFT JOIN devices d ON d.site_id = s.id
+     ${memberFilter}
      GROUP BY s.id
-     ORDER BY s.is_default DESC, LOWER(s.name) ASC`
+     ORDER BY s.is_default DESC, LOWER(s.name) ASC`,
+    restricted ? [req.user!.userId] : []
   );
   res.json(sites.map((s) => ({
     ...s,
@@ -180,4 +190,62 @@ router.post('/:id/devices', requireWrite, async (req: Request, res: Response) =>
   res.json({ ok: true, moved: ids.length });
 });
 
+// ─── SEC-002: site membership management (admin only) ───────────────────────
+
+// GET /api/sites/:id/users — who currently has access to this site
+router.get('/:id/users', requireAdmin, async (req: Request, res: Response) => {
+  const id = parseInt(req.params.id, 10);
+  if (!Number.isInteger(id)) { res.status(400).json({ error: 'Invalid site id' }); return; }
+  const users = await query<{ id: number; username: string; role: string }>(
+    `SELECT u.id, u.username, u.role FROM user_sites us
+       JOIN users u ON u.id = us.user_id
+      WHERE us.site_id = $1
+      ORDER BY u.username`,
+    [id]
+  );
+  res.json(users);
+});
+
+// POST /api/sites/:id/users — grant a user access to this site
+router.post('/:id/users', requireAdmin, async (req: Request, res: Response) => {
+  const id = parseInt(req.params.id, 10);
+  const userId = parseInt(String((req.body as { userId?: unknown }).userId), 10);
+  if (!Number.isInteger(id) || !Number.isInteger(userId)) {
+    res.status(400).json({ error: 'Invalid site id or userId' });
+    return;
+  }
+  const [site, user] = await Promise.all([
+    queryOne<{ id: number }>(`SELECT id FROM sites WHERE id = $1`, [id]),
+    queryOne<{ id: number; role: string }>(`SELECT id, role FROM users WHERE id = $1`, [userId]),
+  ]);
+  if (!site) { res.status(404).json({ error: 'Site not found' }); return; }
+  if (!user) { res.status(404).json({ error: 'User not found' }); return; }
+  if (user.role === 'admin') {
+    // Admins already see every site implicitly; a membership row for one
+    // would be dead data and would misleadingly suggest their access is
+    // scoped.
+    res.status(400).json({ error: 'Admins already have access to every site' });
+    return;
+  }
+  await query(
+    `INSERT INTO user_sites (user_id, site_id) VALUES ($1, $2) ON CONFLICT DO NOTHING`,
+    [userId, id]
+  );
+  invalidateUserSiteCache(userId);
+  res.status(201).json({ ok: true });
+});
+
+// DELETE /api/sites/:id/users/:userId — revoke a user's access to this site
+router.delete('/:id/users/:userId', requireAdmin, async (req: Request, res: Response) => {
+  const id = parseInt(req.params.id, 10);
+  const userId = parseInt(req.params.userId, 10);
+  if (!Number.isInteger(id) || !Number.isInteger(userId)) {
+    res.status(400).json({ error: 'Invalid site id or userId' });
+    return;
+  }
+  await query(`DELETE FROM user_sites WHERE site_id = $1 AND user_id = $2`, [id, userId]);
+  invalidateUserSiteCache(userId);
+  res.json({ ok: true });
+});
+
 export default router;
diff --git a/backend/src/routes/switches.ts b/backend/src/routes/switches.ts
index 8bc530d..79aead7 100644
--- a/backend/src/routes/switches.ts
+++ b/backend/src/routes/switches.ts
@@ -2,11 +2,12 @@ import { Router, Request, Response } from 'express';
 import { query } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeDevices } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 // GET /api/switches — all switch devices with port statistics
 router.get('/', async (req: Request, res: Response) => {
diff --git a/backend/src/routes/topology.ts b/backend/src/routes/topology.ts
index 6d7a6a5..7c729a7 100644
--- a/backend/src/routes/topology.ts
+++ b/backend/src/routes/topology.ts
@@ -2,7 +2,7 @@ import { Router, Request, Response } from 'express';
 import { query, queryOne } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeDevices, siteScopeByDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { PollerService } from '../services/PollerService';
 import {
   buildTopology,
@@ -13,6 +13,7 @@ import {
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 let pollerService: PollerService | null = null;
 export function setPollerService(p: PollerService): void {
diff --git a/backend/src/routes/wireless.ts b/backend/src/routes/wireless.ts
index cbfb0fc..cffc929 100644
--- a/backend/src/routes/wireless.ts
+++ b/backend/src/routes/wireless.ts
@@ -2,13 +2,14 @@ import { Router, Request, Response } from 'express';
 import { query } from '../config/database';
 import { requireAuth, requireWrite } from '../middleware/auth';
 import { siteScopeDevices, siteScopeByDevice } from '../utils/siteScope';
-import { activeSite } from '../middleware/site';
+import { activeSite, enforceSiteAccess } from '../middleware/site';
 import { DeviceCollector, DeviceRow } from '../services/mikrotik/DeviceCollector';
 import { lookupVendor } from '../utils/oui';
 import { analyzeSpectrum, summarize, BAND_RANGES, parseChannelSpec } from '../utils/rfSpectrum';
 
 const router = Router();
 router.use(requireAuth);
+router.use(enforceSiteAccess);
 
 // ─── Helper ───────────────────────────────────────────────────────────────────
 
diff --git a/backend/src/services/SshKeyService.ts b/backend/src/services/SshKeyService.ts
index 0b8feb3..37ab714 100644
--- a/backend/src/services/SshKeyService.ts
+++ b/backend/src/services/SshKeyService.ts
@@ -17,6 +17,7 @@ import { encrypt, decrypt } from '../utils/crypto';
 import {
   generateDeviceKeyPair, keyFileName, keyComment, isUsablePrivateKey, type KeyStatus,
 } from '../utils/sshKeys';
+import { isValidRouterOsUsername } from '../utils/routerOsUsername';
 import { RouterOSClient } from './mikrotik/RouterOSClient';
 
 const CONNECT_TIMEOUT_MS = 20_000;
@@ -173,6 +174,13 @@ export class SshKeyService {
   async deploy(target: SshTarget, opts: { rotate?: boolean } = {}): Promise<DeviceKeyRow> {
     const username = target.ssh_username?.trim();
     if (!username) throw new Error('No SSH username configured for this device');
+    // SEC-006: username is interpolated unescaped into a RouterOS CLI command
+    // below (`user=${username}`). Validating here, at the point of use, is
+    // defense in depth even though device writes already reject an invalid
+    // username before it reaches storage (routes/devices.ts, deviceCreation.ts).
+    if (!isValidRouterOsUsername(username)) {
+      throw new Error('Stored SSH username contains characters that are not safe to use — fix it in device settings before deploying a key');
+    }
 
     const existing = await this.getKey(target.id);
     const canUseExistingKey = existing && existing.status === 'verified';
diff --git a/backend/src/services/deviceCreation.ts b/backend/src/services/deviceCreation.ts
index eff1777..dda98d4 100644
--- a/backend/src/services/deviceCreation.ts
+++ b/backend/src/services/deviceCreation.ts
@@ -2,6 +2,7 @@ import { query, queryOne } from '../config/database';
 import { encrypt, decrypt } from '../utils/crypto';
 import { parsePort } from '../utils/parsePort';
 import { safeConnectionError } from '../utils/safeClientError';
+import { validateRouterOsUsername } from '../utils/routerOsUsername';
 import { RouterOSClient } from './mikrotik/RouterOSClient';
 import type { PollerService } from './PollerService';
 import type { CredentialPresetRow } from '../routes/credentialPresets';
@@ -112,6 +113,13 @@ export async function createDeviceFromBody(
       body: { error: 'name, ip_address, api_username, api_password are required' },
     };
   }
+  // SEC-006: ssh_username is later interpolated unescaped into a RouterOS CLI
+  // command (services/SshKeyService.ts). Reject an unsafe value at the point
+  // it's first stored, not just where it happens to be used.
+  const sshUsernameError = validateRouterOsUsername(ssh_username);
+  if (sshUsernameError) {
+    return { ok: false, status: 400, body: { error: sshUsernameError } };
+  }
 
   const testClient = new RouterOSClient(ip_address, api_port, api_username, api_password, 10_000);
   let detectedSerial: string | null;
diff --git a/backend/src/utils/__tests__/routerOsUsername.test.ts b/backend/src/utils/__tests__/routerOsUsername.test.ts
new file mode 100644
index 0000000..ce60264
--- /dev/null
+++ b/backend/src/utils/__tests__/routerOsUsername.test.ts
@@ -0,0 +1,40 @@
+import { isValidRouterOsUsername, validateRouterOsUsername } from '../routerOsUsername';
+
+describe('SEC-006: RouterOS SSH username allowlist', () => {
+  it('accepts ordinary usernames', () => {
+    for (const u of ['admin', 'svc-rmm', 'ops_user', 'user.name', 'a1', 'A']) {
+      expect(isValidRouterOsUsername(u)).toBe(true);
+    }
+  });
+
+  it('rejects command-injection payloads that rely on RouterOS token separators', () => {
+    const payloads = [
+      'admin;/system/reboot',
+      'admin /system/reboot',
+      'admin\n/system/reboot',
+      'admin\t/system/reboot',
+      'admin"; /system/reboot; "',
+      'admin$(reboot)',
+      'admin`reboot`',
+      'admin/../root',
+      'admin=x comment=y',
+      '',
+      ' ',
+      'a'.repeat(33), // over the length cap
+    ];
+    for (const p of payloads) {
+      expect(isValidRouterOsUsername(p)).toBe(false);
+    }
+  });
+
+  it('validateRouterOsUsername treats an absent value as fine (field is optional)', () => {
+    expect(validateRouterOsUsername(undefined)).toBeNull();
+    expect(validateRouterOsUsername(null)).toBeNull();
+    expect(validateRouterOsUsername('')).toBeNull();
+  });
+
+  it('validateRouterOsUsername rejects a non-string and an unsafe string with a message', () => {
+    expect(validateRouterOsUsername(123)).toMatch(/string/i);
+    expect(validateRouterOsUsername('admin; reboot')).toMatch(/letters, digits/i);
+  });
+});
diff --git a/backend/src/utils/routerOsUsername.ts b/backend/src/utils/routerOsUsername.ts
new file mode 100644
index 0000000..a42291f
--- /dev/null
+++ b/backend/src/utils/routerOsUsername.ts
@@ -0,0 +1,33 @@
+/**
+ * Positive-allowlist validation for a RouterOS SSH/API username (SEC-006).
+ *
+ * The username is stored by an operator and later interpolated directly into
+ * RouterOS CLI commands sent over an SSH exec channel (see
+ * services/SshKeyService.ts: `/user/ssh-keys/import ... user=${username}`).
+ * Escaping after the fact is fragile — RouterOS's own command parser has its
+ * own quoting rules, not shell rules, so a shell-style escape can still leave
+ * a value that RouterOS itself parses as more than one token. Validating
+ * against a known-safe character set before it is ever stored is simpler and
+ * closes the injection regardless of where the value is later used.
+ *
+ * RouterOS itself limits usernames to letters, digits, and a handful of
+ * punctuation characters, with no whitespace — this allowlist is deliberately
+ * narrower than what the device might tolerate, because "narrower than
+ * necessary but provably safe" is the right trade for a value that ends up
+ * unescaped in a command line.
+ */
+const VALID_USERNAME = /^[A-Za-z0-9][A-Za-z0-9._-]{0,31}$/;
+
+export function isValidRouterOsUsername(username: string): boolean {
+  return VALID_USERNAME.test(username);
+}
+
+/** Returns an error message if invalid, or null if the username is acceptable. */
+export function validateRouterOsUsername(username: unknown): string | null {
+  if (username === null || username === undefined || username === '') return null; // optional field
+  if (typeof username !== 'string') return 'Username must be a string';
+  if (!isValidRouterOsUsername(username)) {
+    return 'Username may only contain letters, digits, "." "_" "-", must start with a letter or digit, and be at most 32 characters';
+  }
+  return null;
+}
diff --git a/backend/src/utils/sessionAuth.ts b/backend/src/utils/sessionAuth.ts
new file mode 100644
index 0000000..c30d470
--- /dev/null
+++ b/backend/src/utils/sessionAuth.ts
@@ -0,0 +1,72 @@
+/**
+ * Server-side JWT revocation (SEC-001).
+ *
+ * JWTs stay stateless for signing/verifying (no DB write on every request),
+ * but every session must be killable before its natural expiry: logout,
+ * a password change, disabling an account, or an admin "sign this user out
+ * everywhere" action. The mechanism is a `token_version` column on `users`:
+ * every signed token embeds the version current at sign time, and a request
+ * is rejected the moment that version no longer matches the row -- bumping
+ * the column *is* the revoke.
+ *
+ * Checking on every request would mean a DB round trip per authenticated
+ * call. A short in-process cache (a few seconds) keeps the common case at
+ * zero extra latency while capping how long a revoked token can keep working
+ * to a small, documented window -- far better than the 24h it had before.
+ */
+import { query, queryOne } from '../config/database';
+
+export interface SessionState {
+  tokenVersion: number;
+  active: boolean;
+  role: string;
+}
+
+interface CacheEntry {
+  state: SessionState | null; // null = user no longer exists
+  cachedAt: number;
+}
+
+const CACHE_TTL_MS = 5_000;
+const cache = new Map<number, CacheEntry>();
+
+async function fetchState(userId: number): Promise<SessionState | null> {
+  const row = await queryOne<{ token_version: number; active: boolean; role: string }>(
+    `SELECT token_version, active, role FROM users WHERE id = $1`,
+    [userId]
+  );
+  return row ? { tokenVersion: row.token_version, active: row.active, role: row.role } : null;
+}
+
+/** Current session state for a user, cached for a few seconds. */
+export async function getSessionState(userId: number): Promise<SessionState | null> {
+  const cached = cache.get(userId);
+  if (cached && Date.now() - cached.cachedAt < CACHE_TTL_MS) {
+    return cached.state;
+  }
+  const state = await fetchState(userId);
+  cache.set(userId, { state, cachedAt: Date.now() });
+  return state;
+}
+
+/**
+ * Bump a user's token_version, invalidating every JWT issued before now for
+ * that account. Used by logout, password change, TOTP disable, account
+ * deactivation, and the admin "revoke sessions" action.
+ *
+ * Returns the new version so callers that also sign a fresh token (e.g.
+ * password-change-while-staying-logged-in flows, if ever added) can embed it.
+ */
+export async function bumpTokenVersion(userId: number): Promise<number> {
+  const rows = await query<{ token_version: number }>(
+    `UPDATE users SET token_version = token_version + 1 WHERE id = $1 RETURNING token_version`,
+    [userId]
+  );
+  cache.delete(userId); // don't serve a stale version for the next CACHE_TTL_MS
+  return rows[0]?.token_version ?? 0;
+}
+
+/** Test seam: clear the cache between tests / after direct DB mutation in tests. */
+export function _resetSessionCacheForTest(): void {
+  cache.clear();
+}
diff --git a/backend/src/utils/siteScope.ts b/backend/src/utils/siteScope.ts
index 958735b..79706ed 100644
--- a/backend/src/utils/siteScope.ts
+++ b/backend/src/utils/siteScope.ts
@@ -1,22 +1,35 @@
 /**
- * Site scoping helpers (issue #130).
+ * Site scoping helpers (issue #130), extended for per-user authorization in
+ * Mission 02 (SEC-002).
  *
  * Every device-derived table hangs off devices(id), so a single site_id on
  * devices scopes clients, events, topology, backups and the rest transitively.
- * These helpers turn an active site into the SQL predicate that does it.
+ * These helpers turn an *effective* site scope into the SQL predicate that
+ * does it.
  *
- * The site id is inlined rather than parameterised, and that is a deliberate
+ * A scope is one of:
+ *   - `null`      unrestricted (the whole fleet) -- admins and API tokens.
+ *   - `number`    exactly one site -- either an explicit selection the caller
+ *                 has already been authorized for (middleware/site.ts), or a
+ *                 restricted user's only accessible site.
+ *   - `number[]`  a restricted user viewing "all sites" (no X-Site-Id sent):
+ *                 scoped to every site they're a member of, which may be
+ *                 empty -- meaning no access to anything, not "everything".
+ *
+ * The id(s) are inlined rather than parameterised, and that is a deliberate
  * choice worth justifying: the collection routes build their WHERE clauses by
  * incrementing a shared $n counter, so injecting a parameter mid-build would
  * mean renumbering every filter in ~23 routes -- exactly the kind of manual
  * bookkeeping that produces silent off-by-one bugs. Inlining is safe here
- * because resolveSiteId() below admits nothing but a positive integer; a value
- * that is not one becomes null (unscoped), never text that reaches SQL.
+ * because every id passing through this module is validated as a positive
+ * integer first (resolveSiteId, or read back from user_sites via a parameterised
+ * query) -- never raw text reaching SQL.
  */
+export type SiteScope = number | number[] | null;
 
 /**
  * Normalise an untrusted site id (header, query string) into either a positive
- * integer or null, where null means "no scoping -- show the whole fleet".
+ * integer or null, where null means "no explicit selection".
  *
  * 'all' is the explicit all-sites view. Anything unparseable is also treated as
  * unscoped rather than rejected, so an existing API consumer that knows nothing
@@ -27,7 +40,7 @@ export function resolveSiteId(raw: unknown): number | null {
   const s = String(raw).trim();
   if (s === '' || s.toLowerCase() === 'all') return null;
   // Matched as a literal digit string rather than via Number(), deliberately.
-  // Number() would accept '1e3', '0x1' and even Arabic-Indic '\u0661\u0662' as
+  // Number() would accept '1e3', '0x1' and even Arabic-Indic '١٢' as
   // integers -- all harmless here, but it makes the safety of inlining rest on
   // coercion trivia. A digits-only regex makes it self-evident instead.
   if (!/^\d+$/.test(s)) return null;
@@ -36,23 +49,41 @@ export function resolveSiteId(raw: unknown): number | null {
   return n;
 }
 
+/**
+ * Collapse a scope to a single concrete site id, or null. For an unrestricted
+ * caller (null) or a restricted user viewing several sites at once (array),
+ * there is no single "the site this belongs to" answer -- callers that need
+ * one (e.g. "which site does a newly created device join") get null and fall
+ * back to their own default-site behavior, same as an admin always has.
+ */
+export function singleSiteOrNull(scope: SiteScope): number | null {
+  return typeof scope === 'number' ? scope : null;
+}
+
+function idList(ids: number[]): string {
+  // An empty IN () is invalid SQL and, more importantly, its intent ("match
+  // nothing") is easy to get backwards. Spell it out instead.
+  return ids.length ? `(${ids.join(',')})` : '(NULL)';
+}
+
 /**
  * Predicate for a query that selects from `devices` itself.
  * Returns null when unscoped, so callers can skip pushing a filter.
  */
-export function siteScopeDevices(siteId: number | null, alias = ''): string | null {
-  if (siteId === null) return null;
+export function siteScopeDevices(scope: SiteScope, alias = ''): string | null {
+  if (scope === null) return null;
   const col = alias ? `${alias}.site_id` : 'site_id';
-  return `${col} = ${siteId}`;
+  return Array.isArray(scope) ? `${col} IN ${idList(scope)}` : `${col} = ${scope}`;
 }
 
 /**
  * Predicate for a query on any table carrying a device_id.
  * `column` is the fully-qualified device id column, e.g. 'c.device_id'.
  */
-export function siteScopeByDevice(siteId: number | null, column = 'device_id'): string | null {
-  if (siteId === null) return null;
-  return `${column} IN (SELECT id FROM devices WHERE site_id = ${siteId})`;
+export function siteScopeByDevice(scope: SiteScope, column = 'device_id'): string | null {
+  if (scope === null) return null;
+  const inner = Array.isArray(scope) ? `site_id IN ${idList(scope)}` : `site_id = ${scope}`;
+  return `${column} IN (SELECT id FROM devices WHERE ${inner})`;
 }
 
 /**
@@ -61,9 +92,10 @@ export function siteScopeByDevice(siteId: number | null, column = 'device_id'):
  * site is selected -- showing them in every site would misrepresent them as
  * that site's own.
  */
-export function siteScopeByNullableDevice(siteId: number | null, column = 'device_id'): string | null {
-  if (siteId === null) return null;
-  return `(${column} IS NOT NULL AND ${column} IN (SELECT id FROM devices WHERE site_id = ${siteId}))`;
+export function siteScopeByNullableDevice(scope: SiteScope, column = 'device_id'): string | null {
+  if (scope === null) return null;
+  const inner = Array.isArray(scope) ? `site_id IN ${idList(scope)}` : `site_id = ${scope}`;
+  return `(${column} IS NOT NULL AND ${column} IN (SELECT id FROM devices WHERE ${inner}))`;
 }
 
 /**
@@ -87,6 +119,8 @@ export function andSite(base: string, predicate: string | null): string {
  *
  * When a site holds every device, its total *is* the global total -- an
  * identity, not an approximation -- so `_global` is both correct and complete.
+ * Only meaningful for a single explicit site; a restricted multi-site scope
+ * has no single tag and callers should fall back to per-site queries instead.
  */
 export function clientSeriesTag(
   siteId: number | null,