Mattermost doesn't properly validate channel membership at the time of data retrieval

GHSA-2xf7-hmf6-p64j · CVE-2026-20796 · GO-2026-4495

Published Feb 13, 2026 · Modified Feb 23, 2026

Description

Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API endpoint.. Mattermost Advisory ID: MMSA-2025-00549

References

ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-20796
PACKAGE https://github.com/mattermost/mattermost
WEB https://mattermost.com/security-updates

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