CVE-2026-27659: Mattermost doesn't properly validate CSRF tokens

March 25, 2026 (updated March 31, 2026)

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to properly validate CSRF tokens in the /api/v4/access_control_policies/{policy_id}/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a crafted request. Mattermost Advisory ID: MMSA-2026-00578

References

github.com/advisories/GHSA-rmhw-c3xr-m3xx
github.com/mattermost/mattermost
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-27659

Code Behaviors & Features

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