What is CVE-2026-4265?

CVE-2026-4265 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 4.3/10. Published 2026-03-16.

How severe is CVE-2026-4265?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Auth bypass in Mattermost

CVE-2026-4265

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading fil…

Vulnerability class: Broken Access Control

EPSS: 0.000 (10.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.

Affected products

Mattermost — versions 11.3.0, 11.2.0, 10.11.0

Weakness classification (CWE)

CWE-863 — Incorrect Authorization

References

MMSA-2025-00553 (vendor-advisory)

Frequently asked questions

What is CVE-2026-4265?: CVE-2026-4265 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 4.3/10. Published 2026-03-16.
How severe is CVE-2026-4265?: Medium severity. CVSS v3 base score is 4.3 out of 10.