What is CVE-2026-28735?

CVE-2026-28735 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 5.4/10. Published 2026-05-22.

How severe is CVE-2026-28735?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Auth bypass in Mattermost

CVE-2026-28735

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via m…

Vulnerability class: Broken Access Control

EPSS: 0.000 (8.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N.

Affected products

Mattermost — versions 11.6.0, 11.5.0, 11.4.0
Mattermost Mattermost_server

Weakness classification (CWE)

CWE-863 — Incorrect Authorization

References

responsibledisclosure@mattermost.com (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-28735?: CVE-2026-28735 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 5.4/10. Published 2026-05-22.
How severe is CVE-2026-28735?: Medium severity. CVSS v3 base score is 5.4 out of 10.