CVE-2026-16453 — Mattermost SAML RelayState forgery allows unauthorized team membership
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to verify the integrity of the SAML RelayState POST parameter which allows an a…
Published: 2026-10-16 · CVSS: 7.1 · CVSS 3.1
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to verify the integrity of the SAML RelayState POST parameter which allows an authenticated SAML user to join any team, including invite-only teams, via forging the team_id or invite_id fields in the RelayState.. Mattermost Advisory ID: MMSA-2026-00727
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7