What is CVE-2026-9571?

CVE-2026-9571 is a medium-severity vulnerability in Mattermost, classified under Authentication Bypass by Primary Weakness. CVSS score: 5.9/10. Published 2026-07-13.

How severe is CVE-2026-9571?

Medium severity. CVSS v3 base score is 5.9 out of 10.

Vulnerability in Mattermost

CVE-2026-9571

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to invalidate OAuth refresh tokens upon user account deactivation, which allows a deactivated user or an attacker in possession of a valid refresh token to obtain new functional access tokens via the OAuth refresh token grant endpoint.. Mattermost Advisory ID: MMSA-2026-00680

Published 2026-07-13 · last modified 2026-07-15.

CVSS v3 metric

CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.003 (21.3th percentile), scored 2026-10-12.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 21.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000

Affected products

Mattermost — versions 11.7.0, 11.6.0, 10.11.0
Mattermost Server

Weakness classification (CWE)

CWE-305 — Authentication Bypass by Primary Weakness

References

mattermost.com/security-updates (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-9571?: CVE-2026-9571 is a medium-severity vulnerability in Mattermost, classified under Authentication Bypass by Primary Weakness. CVSS score: 5.9/10. Published 2026-07-13.
How severe is CVE-2026-9571?: Medium severity. CVSS v3 base score is 5.9 out of 10.