CVE-2026-40487 Postiz Has Unrestricted File Upload via MIME Type Spoofing that Leads to Stored XSS
Authenticated users can upload malicious files via MIME spoofing, leading to stored XSS and potential account takeover in Postiz.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-40487?
CVE-2026-40487 is a high-severity vulnerability in gitroomhq postiz-app, published on 18 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Postiz is an AI social media scheduling tool. Prior to version 2.21.6, a file upload validation bypass allows any authenticated user to upload arbitrary HTML, SVG, or other executable file types to the server by spoofing the `Content-Type` header. The uploaded files are then served by nginx with a Content-Type derived from their original extension (`text/html`, `image/svg+xml`), enabling Stored Cross-Site Scripting (XSS) in the context of the application's origin. This can lead to session riding, account takeover, and full compromise of other users' accounts. Version 2.21.6 contains a fix.
Which versions are affected by CVE-2026-40487?
It affects 1 product.
Products include Gitroom Postiz.
How do I fix CVE-2026-40487?
No fix has been published for CVE-2026-40487 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-40487 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40487 exists.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in gitroomhq postiz-app
- CVE-2026-42298 Postiz: Arbitrary Code Execution and Token Exfiltration in pr-docker-build.yml via untrusted Dockerfile.dev
- CVE-2026-42556 Postiz stored XSS in public preview page
- CVE-2026-34577 Postiz: Unauthenticated Full-Read SSRF via /public/stream Endpoint with Trivially Bypassable Extension Check
- CVE-2026-34576 Postiz: SSRF in upload-from-url endpoint allows fetching internal resources and cloud metadata
- CVE-2026-40168 Postiz has Server-Side Request Forgery via Redirect Bypass in /api/public/stream
Sources
Also known as GHSA-44wg-r34q-hvfx.