What is CVE-2026-86349?

CVE-2026-86349 is a medium-severity vulnerability in Mattermost, classified under Inefficient Algorithmic Complexity. CVSS score: 4.3/10. Published 2026-09-14.

How severe is CVE-2026-86349?

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

Vulnerability in Mattermost

CVE-2026-86349

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707

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:N/A:L.

Affected products

Mattermost

Weakness classification (CWE)

CWE-407 — Inefficient Algorithmic Complexity

References

responsibledisclosure@mattermost.com (vendor-advisory)

Frequently asked questions

What is CVE-2026-86349?: CVE-2026-86349 is a medium-severity vulnerability in Mattermost, classified under Inefficient Algorithmic Complexity. CVSS score: 4.3/10. Published 2026-09-14.
How severe is CVE-2026-86349?: Medium severity. CVSS v3 base score is 4.3 out of 10.