What is CVE-2026-16453?

CVE-2026-16453 is a high-severity vulnerability in Mattermost, classified under CWE-472. CVSS score: 7.1/10. Published 2026-10-16.

How severe is CVE-2026-16453?

High severity. CVSS v3 base score is 7.1 out of 10.

Vulnerability in Mattermost

CVE-2026-16453

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

Published 2026-10-16 · last modified 2026-10-16.

CVSS v3 metric

CVSS v3 base score 7.1 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Mattermost

Weakness classification (CWE)

CWE-472

References

mattermost.com/security-updates (vendor-advisory)

Frequently asked questions

What is CVE-2026-16453?: CVE-2026-16453 is a high-severity vulnerability in Mattermost, classified under CWE-472. CVSS score: 7.1/10. Published 2026-10-16.
How severe is CVE-2026-16453?: High severity. CVSS v3 base score is 7.1 out of 10.