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, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765

[ Fixes ]Fixes and patches

No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.

[ Advisories ]Government CERT advisories

• BSI CERT-Bund15 Oct 2026WID-SEC-2026-4009

  Mattermost: Multiple vulnerabilities Translated from German

  CVE-2026-18551CVE-2026-16251CVE-2026-19621+11 more CVEs

[ References ]References

• mattermost.com/security-updates