Vulnerability in Mattermost

[ Description ]Official description

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to validate the target post ID in the Agents plugin's mention reminder component, which allows an authenticated user who can post in a channel visible to a system administrator to cause the administrator's browser to send an unintended API request, resulting in replacement of an installed plugin and code execution on the server, via a crafted post containing a forged mention reminder that the administrator clicks. Mattermost Advisory ID: MMSA-2026-00742

[ Fixes ]Fixes and patches

• Security bulletin: Mattermost MMSA-2026-00742Vendor patch or bulletin · CERT-FR · mattermost.com/security-updates, cited by CERT-FR CERTFR-2026-AVI-1409

[ Advisories ]Government CERT advisories

• BSI CERT-Bund29 Oct 2026WID-SEC-2026-4258

  Mattermost: Vulnerability allows code execution Translated from German

  CVE-2026-93851
• CERT-FR29 Oct 2026CERTFR-2026-AVI-1409

  Vulnerability in Mattermost Server Translated from French

  A vulnerability has been discovered in Mattermost Server. It allows an attacker to cause a security policy bypass.

  CVE-2026-93851

[ References ]References

• mattermost.com/security-updates