CVE-2026-40487
Postiz Has Unrestricted File Upload via MIME Type Spoofing that Leads to Stored XSS
- Published
- Apr 18, 2026
- Updated
- Apr 20, 2026
- Assigning CNA
- GitHub_M
- Evidence observed
- Aug 25, 2026
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:HLow · next 30 days
- Percentile
- 13.3%
- Model date
- Sep 21, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
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.
Sources
1- CVE-2026-40487Exploit
Proof-of-concept exploit for CVE-2026-40487, demonstrating arbitrary file upload via MIME spoofing leading to stored XSS and account takeover in Postiz. Includes multiple attack modes for data exfiltration, privilege escalation, and persistence.
Responsible use
Use vulnerability information only on systems you own or are authorized to test. Kitploit links to public research metadata and does not store exploit code or malicious payloads.