diff --git a/backend/__tests__/middleware/ownership.filterOwnedEventIds.test.js b/backend/__tests__/middleware/ownership.filterOwnedEventIds.test.js
new file mode 100644
index 00000000..066080c0
--- /dev/null
+++ b/backend/__tests__/middleware/ownership.filterOwnedEventIds.test.js
@@ -0,0 +1,78 @@
+/**
+ * Regression test for the bulk archive/delete ownership bypass.
+ *
+ * bulk-archive and bulk-delete acted on body-supplied event ids with no
+ * ownership filter, so an admin/editor scoped to their own events (the
+ * single-event routes enforce requireEventOwnership) could archive or
+ * cascade-delete ANY event by id. filterOwnedEventIds is the helper those
+ * routes now use to drop foreign/non-existent ids.
+ */
+
+// events owned by admin 7; event 3 owned by someone else; event 4 is
+// ownerless (legacy). The mock models:
+//   whereIn('id', ids).andWhere(created_by IS NULL OR created_by = admin.id)
+const EVENTS = [
+  { id: 1, created_by: 7 },
+  { id: 2, created_by: 7 },
+  { id: 3, created_by: 99 },   // foreign
+  { id: 4, created_by: null }, // ownerless/legacy
+];
+
+jest.mock('../../src/database/db', () => ({
+  db: () => {
+    const q = {
+      _ids: null,
+      _adminId: null,
+      whereIn(_col, ids) { this._ids = ids; return this; },
+      andWhere(cb) {
+        // Emulate the (created_by IS NULL OR created_by = admin.id) builder
+        // by capturing the admin id the callback closes over via a probe.
+        const probe = {
+          _adminId: null,
+          whereNull() { return this; },
+          orWhere(_col, id) { this._adminId = id; return this; },
+        };
+        cb(probe);
+        this._adminId = probe._adminId;
+        return this;
+      },
+      select() {
+        return Promise.resolve(
+          EVENTS
+            .filter((e) => this._ids.includes(e.id))
+            .filter((e) => e.created_by === null || e.created_by === this._adminId)
+            .map((e) => ({ id: e.id }))
+        );
+      },
+    };
+    return q;
+  },
+}));
+
+const { filterOwnedEventIds } = require('../../src/middleware/ownership');
+
+describe('filterOwnedEventIds', () => {
+  it('super_admin gets every id, nothing denied', async () => {
+    const { allowed, denied } = await filterOwnedEventIds(
+      { id: 7, roleName: 'super_admin' }, [1, 3, 4, 999]
+    );
+    expect(allowed).toEqual([1, 3, 4, 999]);
+    expect(denied).toEqual([]);
+  });
+
+  it('non-super_admin keeps owned + ownerless, denies foreign and non-existent', async () => {
+    const { allowed, denied } = await filterOwnedEventIds(
+      { id: 7, roleName: 'admin' }, [1, 2, 3, 4, 999]
+    );
+    expect(allowed.sort()).toEqual([1, 2, 4]);   // owns 1,2; 4 is ownerless
+    expect(denied.sort()).toEqual([3, 999]);      // 3 foreign, 999 missing
+  });
+
+  it('foreign-only request yields empty allowed', async () => {
+    const { allowed, denied } = await filterOwnedEventIds(
+      { id: 7, roleName: 'editor' }, [3]
+    );
+    expect(allowed).toEqual([]);
+    expect(denied).toEqual([3]);
+  });
+});
diff --git a/backend/__tests__/middleware/photoAuth.thumbnailScope.test.js b/backend/__tests__/middleware/photoAuth.thumbnailScope.test.js
new file mode 100644
index 00000000..df4050f7
--- /dev/null
+++ b/backend/__tests__/middleware/photoAuth.thumbnailScope.test.js
@@ -0,0 +1,103 @@
+/**
+ * Regression test for the cross-event thumbnail enumeration leak.
+ *
+ * Thumbnails are served flat from /thumbnails/thumb_<name> with
+ * deterministic, enumerable filenames. photoAuth previously granted any
+ * holder of a gallery token for ANY active event access to ANY thumbnail
+ * (it set eventSlug=null and returned next() as long as the token's event
+ * existed), so a visitor to one gallery could pull another (password-
+ * protected) gallery's entire thumbnail set. The fix scopes thumbnail
+ * access to the token's event by matching the requested file against
+ * photos.thumbnail_path for that event_id.
+ */
+
+process.env.JWT_SECRET = 'test-secret-thumbnail-scope-000000000000';
+
+const jwt = require('jsonwebtoken');
+
+// Two events, each owning one thumbnail. The photos mock resolves a row
+// only when BOTH event_id and thumbnail_path match — i.e. it models the
+// real ownership query.
+const EVENTS = [
+  { id: 10, slug: 'event-a', is_active: 1 },
+  { id: 20, slug: 'event-b', is_active: 1 },
+];
+const PHOTOS = [
+  { id: 1, event_id: 10, thumbnail_path: 'thumbnails/thumb_event-a_ceremony_0001.jpg' },
+  { id: 2, event_id: 20, thumbnail_path: 'thumbnails/thumb_event-b_ceremony_0001.jpg' },
+];
+
+jest.mock('../../src/database/db', () => ({
+  db: (table) => ({
+    _cond: null,
+    where(cond) { this._cond = cond; return this; },
+    first() {
+      if (table === 'events') {
+        return Promise.resolve(EVENTS.find((e) => e.id === this._cond.id) || null);
+      }
+      if (table === 'photos') {
+        return Promise.resolve(
+          PHOTOS.find((p) => p.event_id === this._cond.event_id
+            && p.thumbnail_path === this._cond.thumbnail_path) || null
+        );
+      }
+      return Promise.resolve(null);
+    },
+  }),
+}));
+
+jest.mock('../../src/utils/logger', () => ({
+  info: jest.fn(), warn: jest.fn(), error: jest.fn(), debug: jest.fn(),
+}));
+
+const photoAuth = require('../../src/middleware/photoAuth');
+
+function galleryToken(eventId) {
+  return jwt.sign({ type: 'gallery', eventId }, process.env.JWT_SECRET, { issuer: 'picpeak-auth' });
+}
+
+function makeReqRes(token, thumbPath) {
+  const req = { path: thumbPath, headers: { authorization: `Bearer ${token}` }, cookies: {} };
+  const res = {
+    statusCode: null,
+    body: null,
+    status(code) { this.statusCode = code; return this; },
+    json(payload) { this.body = payload; return this; },
+  };
+  return { req, res };
+}
+
+describe('photoAuth — thumbnail ownership scoping', () => {
+  it('denies a gallery token for event A fetching event B\'s thumbnail', async () => {
+    const { req, res } = makeReqRes(galleryToken(10), '/thumb_event-b_ceremony_0001.jpg');
+    const next = jest.fn();
+
+    await photoAuth(req, res, next);
+
+    // Access denied: middleware must not pass the request through.
+    expect(next).not.toHaveBeenCalled();
+    expect(res.statusCode).toBeGreaterThanOrEqual(400);
+    expect(req.event).toBeUndefined();
+  });
+
+  it('allows a gallery token to fetch its own event\'s thumbnail', async () => {
+    const { req, res } = makeReqRes(galleryToken(20), '/thumb_event-b_ceremony_0001.jpg');
+    const next = jest.fn();
+
+    await photoAuth(req, res, next);
+
+    expect(next).toHaveBeenCalled();
+    expect(req.event).toMatchObject({ id: 20 });
+  });
+
+  it('denies a traversal / foreign filename that matches no owned thumbnail', async () => {
+    const { req, res } = makeReqRes(galleryToken(10), '/thumb_../../etc/passwd');
+    const next = jest.fn();
+
+    await photoAuth(req, res, next);
+
+    expect(next).not.toHaveBeenCalled();
+    expect(res.statusCode).toBeGreaterThanOrEqual(400);
+    expect(req.event).toBeUndefined();
+  });
+});
diff --git a/backend/src/__tests__/verifyGalleryAccess.customerRevoke.test.js b/backend/src/__tests__/verifyGalleryAccess.customerRevoke.test.js
index 1ebbefef..55302bbb 100644
--- a/backend/src/__tests__/verifyGalleryAccess.customerRevoke.test.js
+++ b/backend/src/__tests__/verifyGalleryAccess.customerRevoke.test.js
@@ -101,6 +101,7 @@ describe('verifyGalleryAccess — customer-minted JWT with active assignment', (
   it('allows access when the event_customer_assignments row exists', async () => {
     getGalleryTokenFromRequest.mockReturnValue('tkn');
     jwt.verify.mockReturnValue({
+      type: 'gallery',
       eventId: 42,
       via: 'customer',
       customerId: 7,
@@ -131,6 +132,7 @@ describe('verifyGalleryAccess — customer-minted JWT after revocation', () => {
   it('returns 403 CUSTOMER_ASSIGNMENT_REVOKED when the junction row is gone', async () => {
     getGalleryTokenFromRequest.mockReturnValue('tkn');
     jwt.verify.mockReturnValue({
+      type: 'gallery',
       eventId: 42,
       via: 'customer',
       customerId: 7,
@@ -160,6 +162,7 @@ describe('verifyGalleryAccess — customer-minted JWT after revocation', () => {
     // and start 403'ing per-event-password sessions.
     getGalleryTokenFromRequest.mockReturnValue('tkn');
     jwt.verify.mockReturnValue({
+      type: 'gallery',
       eventId: 42,
       customerId: 7,
       // intentionally no `via` claim
@@ -191,6 +194,7 @@ describe('verifyGalleryAccess — per-event-password JWT', () => {
   it('does NOT touch event_customer_assignments and passes through', async () => {
     getGalleryTokenFromRequest.mockReturnValue('tkn');
     jwt.verify.mockReturnValue({
+      type: 'gallery',
       eventId: 42,
       // No via, no customerId — this is the legacy per-event-password
       // flow where every guest mints their own JWT after entering the
diff --git a/backend/src/middleware/auth.js b/backend/src/middleware/auth.js
index 214485f1..ccb49903 100644
--- a/backend/src/middleware/auth.js
+++ b/backend/src/middleware/auth.js
@@ -18,6 +18,7 @@ async function adminAuth(req, res, next) {
     let decoded;
     try {
       decoded = jwt.verify(token, process.env.JWT_SECRET, {
+        algorithms: ['HS256'],
         issuer: 'picpeak-auth',
         complete: true
       });
@@ -140,6 +141,7 @@ async function galleryAuth(req, res, next) {
     let decoded;
     try {
       decoded = jwt.verify(token, process.env.JWT_SECRET, {
+        algorithms: ['HS256'],
         issuer: 'picpeak-auth',
         complete: true
       });
@@ -209,7 +211,7 @@ async function photoAuth(req, res, next) {
 
     let decoded;
     try {
-      decoded = jwt.verify(token, process.env.JWT_SECRET);
+      decoded = jwt.verify(token, process.env.JWT_SECRET, { algorithms: ['HS256'] });
     } catch (err) {
       return res.status(401).json({ error: 'Invalid token' });
     }
diff --git a/backend/src/middleware/customerAuth.js b/backend/src/middleware/customerAuth.js
index 1d2e717b..e1b9c545 100644
--- a/backend/src/middleware/customerAuth.js
+++ b/backend/src/middleware/customerAuth.js
@@ -34,6 +34,7 @@ async function customerAuth(req, res, next) {
     let decoded;
     try {
       const verified = jwt.verify(token, process.env.JWT_SECRET, {
+        algorithms: ['HS256'],
         issuer: 'picpeak-auth',
         complete: true,
       });
diff --git a/backend/src/middleware/gallery.js b/backend/src/middleware/gallery.js
index 8d4ccf56..a1ee968a 100644
--- a/backend/src/middleware/gallery.js
+++ b/backend/src/middleware/gallery.js
@@ -66,18 +66,29 @@ async function verifyGalleryAccess(req, res, next) {
     let decoded;
     try {
       decoded = jwt.verify(token, process.env.JWT_SECRET, {
+        algorithms: ['HS256'],
         issuer: 'picpeak-auth'
       });
     } catch (error) {
       // If verification fails with issuer, try without issuer (backward compatibility)
       if (error.name === 'JsonWebTokenError' && error.message.includes('jwt issuer invalid')) {
-        decoded = jwt.verify(token, process.env.JWT_SECRET);
+        decoded = jwt.verify(token, process.env.JWT_SECRET, { algorithms: ['HS256'] });
       } else {
         throw error;
       }
     }
     logger.debug('[verifyGalleryAccess] Token decoded successfully', { eventId: decoded.eventId, slug: requestedSlug });
-    
+
+    // Only gallery-scoped tokens grant gallery access. Every legitimate
+    // path (password login, share link, client access, customer-minted,
+    // slideshow) mints type:'gallery'. Reject anything else — e.g. a guest
+    // identity token (type:'guest', for feedback attribution) that carries a
+    // matching eventId — instead of relying on other token types incidentally
+    // lacking an eventId to fail the id match below.
+    if (decoded.type !== 'gallery') {
+      return res.status(403).json({ error: 'Invalid token type for gallery access' });
+    }
+
     // If we have a slug in the URL params or from pre-middleware, verify it matches
     if (requestedSlug) {
       // Verify by slug and ensure it matches the token's event
diff --git a/backend/src/middleware/guestAuth.js b/backend/src/middleware/guestAuth.js
index f50e9d1d..a21eddb5 100644
--- a/backend/src/middleware/guestAuth.js
+++ b/backend/src/middleware/guestAuth.js
@@ -23,6 +23,7 @@ async function resolveGuest(req, res, next) {
     let decoded;
     try {
       const verified = jwt.verify(token, process.env.JWT_SECRET, {
+        algorithms: ['HS256'],
         issuer: 'picpeak-auth',
         complete: true,
       });
diff --git a/backend/src/middleware/ownership.js b/backend/src/middleware/ownership.js
index 7ebad2ff..322c0aad 100644
--- a/backend/src/middleware/ownership.js
+++ b/backend/src/middleware/ownership.js
@@ -32,4 +32,36 @@ function requireEventOwnership(req, res, next) {
     });
 }
 
-module.exports = { requireEventOwnership };
+/**
+ * Return the subset of `eventIds` the admin may act on, mirroring
+ * requireEventOwnership for bulk routes that can't use it (they take an
+ * array in the body, not an :id param). super_admin gets everything;
+ * other roles get events they created plus ownerless legacy/system
+ * events (created_by IS NULL). Ids that are foreign OR non-existent both
+ * land in `denied` — deliberately indistinguishable, so bulk routes
+ * don't become an ownership/existence oracle.
+ *
+ * @returns {Promise<{allowed: Array, denied: Array}>}
+ */
+async function filterOwnedEventIds(admin, eventIds) {
+  if (admin.roleName === 'super_admin') {
+    return { allowed: [...eventIds], denied: [] };
+  }
+  const rows = await db('events')
+    .whereIn('id', eventIds)
+    .andWhere((q) => q.whereNull('created_by').orWhere('created_by', admin.id))
+    .select('id');
+  const allowedSet = new Set(rows.map((r) => r.id));
+  const allowed = [];
+  const denied = [];
+  for (const id of eventIds) {
+    if (allowedSet.has(id) || allowedSet.has(Number(id))) {
+      allowed.push(id);
+    } else {
+      denied.push(id);
+    }
+  }
+  return { allowed, denied };
+}
+
+module.exports = { requireEventOwnership, filterOwnedEventIds };
diff --git a/backend/src/middleware/photoAuth.js b/backend/src/middleware/photoAuth.js
index 6f832aa1..df7a1433 100644
--- a/backend/src/middleware/photoAuth.js
+++ b/backend/src/middleware/photoAuth.js
@@ -28,12 +28,13 @@ async function photoAuth(req, res, next) {
         let decoded;
         try {
           decoded = jwt.verify(token, process.env.JWT_SECRET, {
+            algorithms: ['HS256'],
             issuer: 'picpeak-auth'
           });
         } catch (issuerError) {
           // If verification fails with issuer, try without issuer (backward compatibility)
           if (issuerError.name === 'JsonWebTokenError' && issuerError.message.includes('jwt issuer invalid')) {
-            decoded = jwt.verify(token, process.env.JWT_SECRET);
+            decoded = jwt.verify(token, process.env.JWT_SECRET, { algorithms: ['HS256'] });
           } else {
             throw issuerError;
           }
@@ -43,24 +44,36 @@ async function photoAuth(req, res, next) {
         if (decoded.type === 'gallery') {
           // For thumbnails, we need to verify the token is for a valid event
           if (!eventSlug) {
-            // Extract event ID from the decoded token
+            // Resolve the token's event (by id, or legacy slug fallback)...
+            let event = null;
             if (decoded.eventId) {
-              const event = await db('events')
+              event = await db('events')
                 .where({ id: decoded.eventId, is_active: formatBoolean(true) })
                 .first();
-              if (event) {
+            }
+            if (!event && decoded.eventSlug) {
+              event = await db('events')
+                .where({ slug: decoded.eventSlug, is_active: formatBoolean(true) })
+                .first();
+            }
+            // ...then confirm the REQUESTED thumbnail actually belongs to
+            // that event. Thumbnails are stored flat (thumbnails/thumb_<name>)
+            // with deterministic, enumerable filenames derived from the
+            // public event name + a sequential counter. Without this
+            // ownership check any holder of a gallery token for any event
+            // could enumerate and fetch another (password-protected) event's
+            // entire thumbnail set, defeating the gallery password. A
+            // traversal or foreign filename simply fails to match → denied.
+            if (event) {
+              const requestedKey = `thumbnails${req.path}`;
+              const ownsThumbnail = await db('photos')
+                .where({ event_id: event.id, thumbnail_path: requestedKey })
+                .first();
+              if (ownsThumbnail) {
                 req.event = event;
                 return next();
               }
             }
-            // Fallback to slug
-            const event = await db('events')
-              .where({ slug: decoded.eventSlug, is_active: formatBoolean(true) })
-              .first();
-            if (event) {
-              req.event = event;
-              return next();
-            }
           }
           // For regular photos, check if token matches the event
           else if (decoded.eventSlug === eventSlug) {
diff --git a/backend/src/middleware/sessionTimeout.js b/backend/src/middleware/sessionTimeout.js
index 3c7968bb..88ef5dc3 100644
--- a/backend/src/middleware/sessionTimeout.js
+++ b/backend/src/middleware/sessionTimeout.js
@@ -86,7 +86,7 @@ async function sessionTimeoutMiddleware(req, res, next) {
   
   try {
     // Verify token is valid
-    const decoded = jwt.verify(token, process.env.JWT_SECRET);
+    const decoded = jwt.verify(token, process.env.JWT_SECRET, { algorithms: ['HS256'] });
     
     // Check if this is an admin token
     if (!decoded.id) {
@@ -127,7 +127,7 @@ async function sessionTimeoutMiddleware(req, res, next) {
     for (const [oldToken, _] of sessions.entries()) {
       if (oldToken !== token) {
         try {
-          const oldDecoded = jwt.verify(oldToken, process.env.JWT_SECRET);
+          const oldDecoded = jwt.verify(oldToken, process.env.JWT_SECRET, { algorithms: ['HS256'] });
           if (oldDecoded.id === userId) {
             sessions.delete(oldToken);
           }
diff --git a/backend/src/routes/adminEventRename.js b/backend/src/routes/adminEventRename.js
index 00bdbfc4..cc820568 100644
--- a/backend/src/routes/adminEventRename.js
+++ b/backend/src/routes/adminEventRename.js
@@ -7,6 +7,7 @@ const express = require('express');
 const { body, validationResult } = require('express-validator');
 const { adminAuth } = require('../middleware/auth');
 const { requirePermission } = require('../middleware/permissions');
+const { requireEventOwnership } = require('../middleware/ownership');
 const eventRenameService = require('../services/eventRenameService');
 const router = express.Router();
 
@@ -14,7 +15,7 @@ const router = express.Router();
  * POST /api/admin/events/:eventId/rename
  * Rename an event
  */
-router.post('/:eventId/rename', adminAuth, requirePermission('events.edit'), [
+router.post('/:eventId/rename', adminAuth, requirePermission('events.edit'), requireEventOwnership, [
   body('newEventName')
     .trim()
     .isLength({ min: 3, max: 100 })
@@ -59,7 +60,7 @@ router.post('/:eventId/rename', adminAuth, requirePermission('events.edit'), [
  * POST /api/admin/events/:eventId/validate-rename
  * Validate a potential rename without executing it
  */
-router.post('/:eventId/validate-rename', adminAuth, requirePermission('events.edit'), [
+router.post('/:eventId/validate-rename', adminAuth, requirePermission('events.edit'), requireEventOwnership, [
   body('newEventName')
     .trim()
     .isLength({ min: 3, max: 100 })
diff --git a/backend/src/routes/adminEvents.js b/backend/src/routes/adminEvents.js
index 4b30546d..f6040c71 100644
--- a/backend/src/routes/adminEvents.js
+++ b/backend/src/routes/adminEvents.js
@@ -24,7 +24,7 @@ const eventTypeService = require('../services/eventTypeService');
 const { normaliseEventTimeTriple } = require('../services/eventService');
 const { hasColumnCached } = require('../utils/schemaCache');
 const { validateFileType } = require('../utils/fileSecurityUtils');
-const { requireEventOwnership } = require('../middleware/ownership');
+const { requireEventOwnership, filterOwnedEventIds } = require('../middleware/ownership');
 const { requireFeatureFlag } = require('../middleware/requireFeatureFlag');
 const { getAppSetting } = require('../utils/appSettings');
 const { getFrontendBaseUrl } = require('../utils/frontendUrl');
@@ -2260,25 +2260,39 @@ router.post('/bulk-archive', adminAuth, requirePermission('events.archive'), [
     }
 
     const { eventIds } = req.body;
-    
+
     if (eventIds.length === 0) {
       return res.status(400).json({ error: 'No events selected for archiving' });
     }
 
-    // Get all events to archive
-    const events = await db('events')
-      .whereIn('id', eventIds)
-      .where('is_archived', formatBoolean(false));
-
-    if (events.length === 0) {
-      return res.status(400).json({ error: 'No valid events found to archive' });
-    }
+    // Ownership scope: a non-super_admin may only archive events they own.
+    // Foreign/non-existent ids are dropped and reported as failures so this
+    // route can't archive another admin's events (the single-event
+    // /:id/archive route enforces the same via requireEventOwnership).
+    const { allowed: allowedIds, denied: deniedIds } = await filterOwnedEventIds(req.admin, eventIds);
 
     const results = {
       successful: [],
-      failed: []
+      failed: deniedIds.map((id) => ({ id, name: null, error: 'Access denied or event not found' }))
     };
 
+    // Get all events to archive
+    const events = allowedIds.length
+      ? await db('events')
+        .whereIn('id', allowedIds)
+        .where('is_archived', formatBoolean(false))
+      : [];
+
+    if (events.length === 0) {
+      if (results.failed.length > 0) {
+        return res.json({
+          message: `Bulk archive completed: 0 succeeded, ${results.failed.length} failed`,
+          results
+        });
+      }
+      return res.status(400).json({ error: 'No valid events found to archive' });
+    }
+
     // Process each event
     for (const event of events) {
       try {
@@ -2353,16 +2367,21 @@ router.post('/bulk-delete', adminAuth, requirePermission('events.delete'), [
 
     const { eventIds } = req.body;
 
-    // Editor-role events.delete permission is already gated by the route
-    // middleware. We do NOT additionally filter to created_by here because
-    // the per-event delete-cascade is global (matches DELETE /:id which
-    // also has no role-based filter — that's why events.delete is a
-    // sensitive permission).
+    // Ownership scope: a non-super_admin may only delete events they own.
+    // The single-event DELETE /:id route enforces this via
+    // requireEventOwnership; this bulk route must match it, otherwise an
+    // admin/editor scoped to their own events could cascade-delete any
+    // event by id. Foreign/non-existent ids are dropped and reported as
+    // failures (indistinguishable, to avoid an existence oracle).
+    const { allowed: allowedIds, denied: deniedIds } = await filterOwnedEventIds(req.admin, eventIds);
 
-    const results = { successful: [], failed: [] };
+    const results = {
+      successful: [],
+      failed: deniedIds.map((id) => ({ id, name: null, error: 'Access denied or event not found' }))
+    };
     const adminContext = { id: req.admin.id, username: req.admin.username };
 
-    for (const eventId of eventIds) {
+    for (const eventId of allowedIds) {
       try {
         const deleted = await deleteEventCascade(eventId, adminContext);
         results.successful.push(deleted);
diff --git a/backend/src/routes/adminExternalMedia.js b/backend/src/routes/adminExternalMedia.js
index 8566bfff..de9e6c06 100644
--- a/backend/src/routes/adminExternalMedia.js
+++ b/backend/src/routes/adminExternalMedia.js
@@ -3,6 +3,7 @@ const path = require('path');
 const fs = require('fs').promises;
 const { adminAuth } = require('../middleware/auth');
 const { requirePermission } = require('../middleware/permissions');
+const { requireEventOwnership } = require('../middleware/ownership');
 const { list, resolveExternalPath, getExternalMediaRoot } = require('../services/externalMediaService');
 const { db, logActivity } = require('../database/db');
 const sharp = require('sharp');
@@ -48,7 +49,7 @@ async function walkDir(dir, baseDir) {
 
 // POST /api/admin/events/:id/import-external
 // Body: { external_path: string, recursive?: boolean, map?: { individual?: string, collages?: string } }
-router.post('/events/:id/import-external', adminAuth, requirePermission('photos.upload'), async (req, res) => {
+router.post('/events/:id/import-external', adminAuth, requirePermission('photos.upload'), requireEventOwnership, async (req, res) => {
   try {
     const eventId = parseInt(req.params.id);
     const { external_path, recursive = true, map = { individual: 'individual', collages: 'collages' } } = req.body || {};
diff --git a/backend/src/routes/adminPhotos.js b/backend/src/routes/adminPhotos.js
index 50496a52..56429d8d 100644
--- a/backend/src/routes/adminPhotos.js
+++ b/backend/src/routes/adminPhotos.js
@@ -601,12 +601,18 @@ router.post(
       const photo = await db('photos').where({ id: req.params.photoId }).first();
       if (!photo) return res.status(404).json({ error: 'Photo not found' });
 
-      // Editor role: only allow retry on photos in events they own.
-      if (req.admin.roleName === 'editor') {
+      // Ownership scope: any non-super_admin may only retry photos in events
+      // they own — matching requireEventOwnership (which scopes both the
+      // admin and editor roles; only super_admin bypasses). Previously this
+      // checked the editor role alone, leaving admin-role users able to
+      // reprocess another admin's photos.
+      if (req.admin.roleName !== 'super_admin') {
         const event = await db('events')
-          .where({ id: photo.event_id, created_by: req.admin.id })
+          .where({ id: photo.event_id })
           .first();
-        if (!event) return res.status(404).json({ error: 'Photo not found' });
+        if (event && event.created_by && event.created_by !== req.admin.id) {
+          return res.status(404).json({ error: 'Photo not found' });
+        }
       }
 
       if (photo.processing_status !== 'failed') {
diff --git a/backend/src/routes/auth.js b/backend/src/routes/auth.js
index e99b5861..3ad12e8c 100644
--- a/backend/src/routes/auth.js
+++ b/backend/src/routes/auth.js
@@ -14,6 +14,7 @@ const {
 } = require('../utils/authSecurity');
 const { endSession } = require('../middleware/sessionTimeout');
 const { revokeToken } = require('../utils/tokenRevocation');
+const { timingSafeEqualStr } = require('../utils/timingSafe');
 const logger = require('../utils/logger');
 const {
   setAdminAuthCookie,
@@ -413,7 +414,7 @@ router.post('/gallery/share-login', [
 
     const expectedToken = getEventShareToken(event);
 
-    if (!expectedToken || token !== expectedToken) {
+    if (!expectedToken || !timingSafeEqualStr(token, expectedToken)) {
       await trackFailedAttempt(shareIdentifier, ipAddress, userAgent);
       return res.status(401).json({ error: 'Invalid or expired share link' });
     }
diff --git a/backend/src/routes/galleryFeedback.js b/backend/src/routes/galleryFeedback.js
index db58bc8a..9ca5f00d 100644
--- a/backend/src/routes/galleryFeedback.js
+++ b/backend/src/routes/galleryFeedback.js
@@ -1,6 +1,5 @@
 const express = require('express');
 const router = express.Router();
-const { photoAuth } = require('../middleware/photoAuth');
 const { verifyGalleryAccess, denySlideshowToken } = require('../middleware/gallery');
 const { feedbackRateLimit, generateGuestIdentifier } = require('../middleware/feedbackRateLimit');
 const { resolveGuest } = require('../middleware/guestAuth');
diff --git a/backend/src/routes/protectedImages.js b/backend/src/routes/protectedImages.js
index 15ddbb1b..572ebcd1 100644
--- a/backend/src/routes/protectedImages.js
+++ b/backend/src/routes/protectedImages.js
@@ -8,6 +8,7 @@ const { getStorage } = require('../services/storage');
 const { resolvePhotoStorageKey, resolvePhotoFilePath } = require('../services/photoResolver');
 const { withLocalCopy } = require('../services/imageProcessor');
 const crypto = require('crypto');
+const { timingSafeEqualStr } = require('../utils/timingSafe');
 
 const router = express.Router();
 
@@ -32,9 +33,9 @@ function verifyImageToken(token) {
     const decoded = Buffer.from(data, 'base64').toString();
     const [photoId, expires] = decoded.split(':');
     
-    // Verify signature
+    // Verify signature (constant-time — avoids leaking the HMAC byte-by-byte)
     const expectedSignature = crypto.createHmac('sha256', secret).update(decoded).digest('hex');
-    if (signature !== expectedSignature) {
+    if (!timingSafeEqualStr(signature, expectedSignature)) {
       return null;
     }
     
diff --git a/backend/src/routes/secureImages.js b/backend/src/routes/secureImages.js
index 79093eee..c4335b54 100644
--- a/backend/src/routes/secureImages.js
+++ b/backend/src/routes/secureImages.js
@@ -1,6 +1,6 @@
 const express = require('express');
 const { db } = require('../database/db');
-const { verifyGalleryAccess } = require('../middleware/gallery');
+const { verifyGalleryAccess, denySlideshowToken } = require('../middleware/gallery');
 const secureImageService = require('../services/secureImageService');
 const secureImageMiddleware = require('../middleware/secureImageMiddleware');
 const logger = require('../utils/logger');
@@ -23,7 +23,7 @@ router.post('/:slug/generate-token', async (req, res, next) => {
   // Add slug to request for verifyGalleryAccess
   req.requestedSlug = req.params.slug;
   next();
-}, verifyGalleryAccess, async (req, res) => {
+}, verifyGalleryAccess, denySlideshowToken, async (req, res) => {
   try {
     const { photoId, accessType = 'view' } = req.body;
     
@@ -273,6 +273,7 @@ router.get('/:slug/secure-download/:photoId/:token',
     next();
   },
   verifyGalleryAccess,
+  denySlideshowToken,
   async (req, res) => {
     try {
       const { photoId, token } = req.params;
diff --git a/backend/src/utils/rateLimitSecurity.js b/backend/src/utils/rateLimitSecurity.js
index d7614f6a..0ba002c4 100644
--- a/backend/src/utils/rateLimitSecurity.js
+++ b/backend/src/utils/rateLimitSecurity.js
@@ -32,7 +32,7 @@ function hasValidAdminToken(req) {
     
     // Critical: Verify token is valid before skipping rate limit
     // This prevents invalid tokens from bypassing rate limiting
-    const decoded = jwt.verify(token, process.env.JWT_SECRET);
+    const decoded = jwt.verify(token, process.env.JWT_SECRET, { algorithms: ['HS256'] });
     
     // Additional validation
     if (!decoded || typeof decoded !== 'object') {
diff --git a/backend/src/utils/timingSafe.js b/backend/src/utils/timingSafe.js
new file mode 100644
index 00000000..9fb4b2e7
--- /dev/null
+++ b/backend/src/utils/timingSafe.js
@@ -0,0 +1,22 @@
+const crypto = require('crypto');
+
+/**
+ * Constant-time string comparison for secrets (share tokens, HMAC
+ * signatures, etc.). Returns false for non-strings or length mismatch
+ * without leaking timing beyond the (non-secret) length. Prevents an
+ * attacker from recovering a token byte-by-byte via response-time
+ * differences of a naive `a === b`.
+ */
+function timingSafeEqualStr(a, b) {
+  if (typeof a !== 'string' || typeof b !== 'string') {
+    return false;
+  }
+  const ab = Buffer.from(a);
+  const bb = Buffer.from(b);
+  if (ab.length !== bb.length) {
+    return false;
+  }
+  return crypto.timingSafeEqual(ab, bb);
+}
+
+module.exports = { timingSafeEqualStr };
diff --git a/frontend/src/components/common/AuthenticatedImage.tsx b/frontend/src/components/common/AuthenticatedImage.tsx
index 71ad2c2f..ea862703 100644
--- a/frontend/src/components/common/AuthenticatedImage.tsx
+++ b/frontend/src/components/common/AuthenticatedImage.tsx
@@ -137,18 +137,26 @@ export const AuthenticatedImage: React.FC<AuthenticatedImageProps> = ({
         throw new Error('No URL provided');
       }
 
-      // Build full URL for the image
+      // Build full URL for the image. Only relative paths are app-owned;
+      // an absolute URL is passed through untouched.
+      const isRelative = rawUrl.startsWith('/');
       const fullImageUrl = rawUrl.startsWith('/admin')
         ? buildResourceUrl(`/api${rawUrl}`)
-        : rawUrl.startsWith('/')
+        : isRelative
           ? buildResourceUrl(rawUrl)
           : rawUrl;
 
       const headers: Record<string, string> = {};
-      const slugForRequest = resolveSlug(rawUrl);
-      const token = getGalleryToken(slugForRequest);
-      if (token) {
-        headers.Authorization = `Bearer ${token}`;
+      // Attach the gallery bearer token ONLY to relative (same-app) image
+      // paths. Never send it to an absolute/external URL — that would leak
+      // gallery credentials cross-origin. AuthenticatedImage does not
+      // support external URLs by design.
+      if (isRelative) {
+        const slugForRequest = resolveSlug(rawUrl);
+        const token = getGalleryToken(slugForRequest);
+        if (token) {
+          headers.Authorization = `Bearer ${token}`;
+        }
       }
 
       const response = await fetch(fullImageUrl, {
diff --git a/frontend/src/config/api.ts b/frontend/src/config/api.ts
index d2e609ae..697afea4 100644
--- a/frontend/src/config/api.ts
+++ b/frontend/src/config/api.ts
@@ -56,11 +56,19 @@ api.interceptors.request.use(
 
       const pathname = rawPath.startsWith('/') ? rawPath : `/${rawPath}`;
 
-      const isGalleryEndpoint = /^\/gallery\//.test(pathname)
-        || /^\/secure-images\//.test(pathname)
-        || /^\/auth\/gallery\//.test(pathname);
+      // Never attach the gallery token to an absolute URL. Requests to the
+      // app's own API use relative paths (axios prepends baseURL); an
+      // absolute URL could point at any origin, and extracting its
+      // `/gallery/...` pathname would otherwise match below and leak the
+      // bearer token cross-origin.
+      const isAbsoluteUrl = /^https?:\/\//i.test(config.url || '');
 
-      const isGallerySessionCheck = pathname === '/auth/session'
+      const isGalleryEndpoint = !isAbsoluteUrl && (
+        /^\/gallery\//.test(pathname)
+        || /^\/secure-images\//.test(pathname)
+        || /^\/auth\/gallery\//.test(pathname));
+
+      const isGallerySessionCheck = !isAbsoluteUrl && pathname === '/auth/session'
         && (!!paramSlug || window.location.pathname.startsWith('/gallery/'));
 
       if (isGalleryEndpoint || isGallerySessionCheck) {