diff --git a/backend/__tests__/routes/adminEventsLogoPathTraversal.test.js b/backend/__tests__/routes/adminEventsLogoPathTraversal.test.js
new file mode 100644
index 00000000..2d64a9bd
--- /dev/null
+++ b/backend/__tests__/routes/adminEventsLogoPathTraversal.test.js
@@ -0,0 +1,122 @@
+/**
+ * GHSA-9q5j-vqfw-32hr — the event-logo upload's multer `filename` callback
+ * built the stored path directly from `req.params.id` with no integer
+ * validation:
+ *
+ *   filename: (req, file, cb) => {
+ *     cb(null, `event-${req.params.id}-logo-${Date.now()}${ext}`);
+ *   }
+ *
+ * A traversal payload in the `:id` route param (URL-encoded so it still
+ * matches a single Express path segment, then decoded back into literal
+ * `../` sequences by Express before handlers see it) could escape the
+ * intended uploads/logos/events/ directory. Most directly reachable via a
+ * super_admin session: requireEventOwnership short-circuits with next() and
+ * zero DB lookup for that role (src/middleware/ownership.js), so nothing
+ * upstream of multer validates the id first.
+ *
+ * Fixed by rejecting any non-positive-integer id before it is used to build
+ * the filename, regardless of role or ownership-check ordering.
+ */
+const path = require('path');
+const fs = require('fs');
+const os = require('os');
+
+process.env.NODE_ENV = 'test';
+process.env.TEST_DATABASE_PATH = path.join(
+  fs.mkdtempSync(path.join(os.tmpdir(), 'picpeak-events-logo-')), 'db.sqlite'
+);
+process.env.JWT_SECRET = process.env.JWT_SECRET || 'admin-events-logo-test-secret';
+
+const express = require('express');
+const cookieParser = require('cookie-parser');
+const request = require('supertest');
+const { bootCrmDb, seedMinimal, assignAdminRole, mintAdminToken } = require('../integration/helpers/crmDb');
+
+async function insertEvent(db, adminId, over = {}) {
+  const base = {
+    slug: `ev-${Math.random().toString(16).slice(2)}`,
+    event_type: 'wedding',
+    event_name: 'Test Wedding',
+    event_date: '2026-05-29',
+    host_email: 'host@example.com',
+    admin_email: 'admin@example.com',
+    password_hash: 'x',
+    share_link: `/gallery/share-${Math.random().toString(16).slice(2)}`,
+    share_token: `st-${Math.random().toString(16).slice(2)}`,
+    expires_at: new Date(Date.now() + 7 * 24 * 3600 * 1000).toISOString(),
+    is_active: 1, is_archived: 0, is_draft: 0,
+    created_by: adminId,
+    created_at: new Date().toISOString(),
+    ...over,
+  };
+  const r = await db('events').insert(base).returning('id');
+  return r[0]?.id ?? r[0];
+}
+
+describe('POST /api/admin/events/:id/logo — path traversal guard', () => {
+  let db; let cleanup; let app; let adminId; let token;
+
+  beforeAll(async () => {
+    ({ db, cleanup } = await bootCrmDb());
+    ({ adminId } = await seedMinimal(db));
+    // super_admin: requireEventOwnership short-circuits with no DB lookup
+    // for this role, so it reaches multer with nothing upstream having
+    // validated the id — the exact path GHSA-9q5j-vqfw-32hr exploited.
+    await assignAdminRole(db, adminId, 'super_admin');
+    token = mintAdminToken(adminId);
+
+    app = express();
+    app.use(express.json());
+    app.use(cookieParser());
+    app.use('/api/admin/events', require('../../src/routes/adminEvents'));
+    // eslint-disable-next-line no-unused-vars
+    app.use((err, req, res, next) => {
+      res.status(err.statusCode || err.status || 500).json({ error: err.message, code: err.code });
+    });
+  }, 120000);
+
+  afterAll(async () => { await cleanup(); });
+
+  const auth = (req) => req.set('Authorization', `Bearer ${token}`);
+  const logoDir = () => path.join(process.env.STORAGE_PATH, 'uploads/logos/events');
+
+  it('rejects a traversal payload in the id param instead of writing outside uploads/logos/events', async () => {
+    // '../../../../tmp/pwned' URL-encoded so the raw request path still has
+    // a single segment (matches Express's `:id`), but Express decodes the
+    // param back into literal '../' sequences before the route sees it.
+    const traversalId = encodeURIComponent('../../../../tmp/pwned');
+
+    const res = await auth(
+      request(app).post(`/api/admin/events/${traversalId}/logo`)
+    ).attach('logo', Buffer.from('fake image data'), 'logo.png');
+
+    expect(res.status).toBeGreaterThanOrEqual(400);
+    expect(res.body.error).toMatch(/invalid event id/i);
+
+    // No file should have been written anywhere — the filename callback
+    // must error out before multer opens a write stream.
+    const escapedFile = path.join(os.tmpdir(), 'pwned');
+    expect(fs.existsSync(escapedFile)).toBe(false);
+    if (fs.existsSync(logoDir())) {
+      expect(fs.readdirSync(logoDir())).toHaveLength(0);
+    }
+  });
+
+  it('still accepts a normal numeric event id', async () => {
+    const id = await insertEvent(db, adminId, { event_name: 'Logo Event' });
+
+    const res = await auth(
+      request(app).post(`/api/admin/events/${id}/logo`)
+    ).attach('logo', Buffer.from('fake image data'), 'logo.png');
+
+    expect(res.status).toBe(200);
+    expect(res.body.hero_logo_url).toMatch(new RegExp(`^/uploads/logos/events/event-${id}-logo-`));
+
+    const files = fs.readdirSync(logoDir());
+    expect(files.some((f) => f.startsWith(`event-${id}-logo-`))).toBe(true);
+
+    const row = await db('events').where({ id }).first();
+    expect(row.hero_logo_url).toBe(res.body.hero_logo_url);
+  });
+});
diff --git a/backend/src/routes/adminEvents/logo.js b/backend/src/routes/adminEvents/logo.js
index 2e33fee6..6e7ea9ef 100644
--- a/backend/src/routes/adminEvents/logo.js
+++ b/backend/src/routes/adminEvents/logo.js
@@ -23,8 +23,12 @@ const eventLogoStorage = multer.diskStorage({
     cb(null, uploadDir);
   },
   filename: (req, file, cb) => {
+    const eventId = Number(req.params.id);
+    if (!Number.isInteger(eventId) || eventId <= 0) {
+      return cb(new Error('Invalid event id'));
+    }
     const ext = path.extname(file.originalname);
-    cb(null, `event-${req.params.id}-logo-${Date.now()}${ext}`);
+    cb(null, `event-${eventId}-logo-${Date.now()}${ext}`);
   }
 });