What’s Vulnerable › Vulnerabilities

CVE-2026-40487: Postiz Has Unrestricted File Upload via MIME Type Spoofing that Leads to Stored XSS

• Severity: critical (CVSS 9.0 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-04-18 · updated 2026-10-26
• Weakness: CWE-79

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.

Affected products

• gitroomhq postiz-app: before 2.21.6 — fixed in 2.21.6

How to fix

Upgrade to a fixed version: gitroomhq postiz-app 2.21.6. Check the vendor advisory for mitigations.

References

• https://github.com/gitroomhq/postiz-app/releases/tag/v2.21.6
• https://github.com/gitroomhq/postiz-app/security/advisories/GHSA-44wg-r34q-hvfx
• https://github.com/gitroomhq/postiz-app/security/advisories/GHSA-44wg-r34q-hvfx

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