What is CVE-2026-18795?

CVE-2026-18795 is a medium-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 6.4/10. Published 2026-10-16.

How severe is CVE-2026-18795?

Medium severity. CVSS v3 base score is 6.4 out of 10.

Auth bypass in Mattermost

CVE-2026-18795

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756

Vulnerability class: Broken Access Control

Published 2026-10-16 · last modified 2026-10-16.

CVSS v3 metric

CVSS v3 base score 6.4 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Mattermost

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

mattermost.com/security-updates (vendor-advisory)

Frequently asked questions

What is CVE-2026-18795?: CVE-2026-18795 is a medium-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 6.4/10. Published 2026-10-16.
How severe is CVE-2026-18795?: Medium severity. CVSS v3 base score is 6.4 out of 10.