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Fencer Vulns
high 8.9

CVE-2026-40487 json

Postiz Has Unrestricted File Upload via MIME Type Spoofing that Leads to Stored XSS

published 2026-04-18 6 mo ago modified 2026-10-26 13 d ago also EUVD-2026-23634

cvss
8.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

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.

Patch / fix

  • gitroom postiz 2.21.6

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
6 mo ago

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/gitroomhq/postiz-app/security/advisories/GHSA-44wg-r34q-hvfx referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 8.9 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:L
NVD 3.1 9.0 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

Affected products

  • gitroomhq postiz-app

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation
  • CWE-345 Insufficient Verification of Data Authenticity
  • CWE-434 Unrestricted Upload of File with Dangerous Type

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.