What is CVE-2026-6334?

CVE-2026-6334 is a low-severity vulnerability in Mattermost, classified under Authentication Bypass by Primary Weakness. CVSS score: 3.1/10. Published 2026-05-18.

How severe is CVE-2026-6334?

Low severity. CVSS v3 base score is 3.1 out of 10.

Vulnerability in Mattermost

CVE-2026-6334

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermost Advisory ID: MMSA-2026-00570

Published 2026-05-18 · last modified 2026-06-17.

CVSS v3 metric

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

EPSS exploit prediction

EPSS: 0.002 (8.8th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 9th percentile — 8.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.001

Affected products

Mattermost — versions 11.5.0, 10.11.0, 11.6.0
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-2026-6334?: CVE-2026-6334 is a low-severity vulnerability in Mattermost, classified under Authentication Bypass by Primary Weakness. CVSS score: 3.1/10. Published 2026-05-18.
How severe is CVE-2026-6334?: Low severity. CVSS v3 base score is 3.1 out of 10.