What is CVE-2026-3109?

CVE-2026-3109 is a low-severity vulnerability in Mattermost, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 2.2/10. Published 2026-03-26.

How severe is CVE-2026-3109?

Low severity. CVSS v3 base score is 2.2 out of 10.

Vulnerability in Mattermost

CVE-2026-3109

Mattermost Plugins versions <=11.4 10.11.11.0 fail to validate webhook request timestamps which allows an attacker to corrupt Zoom meeting state in Mattermost via replayed webhook requests. Mattermost Advisory ID: MMSA-2026-00584

Published 2026-03-26 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 2.2 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.003 (21.2th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 21.2% 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 0, 11.5.0, 10.11.12
Mattermost Server

Weakness classification (CWE)

CWE-754 — Improper Check for Unusual or Exceptional Conditions

References

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

Frequently asked questions

What is CVE-2026-3109?: CVE-2026-3109 is a low-severity vulnerability in Mattermost, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 2.2/10. Published 2026-03-26.
How severe is CVE-2026-3109?: Low severity. CVSS v3 base score is 2.2 out of 10.