CVE-2026-86349

Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting

State: Published
Severity: 4.3 Medium
Published: Sep 14, 2026
Updated: Sep 14, 2026
Reserved: Sep 7, 2026

Description

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

Scores

CVSS	Score	Vector	Source
3.1	4.3 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L	Mattermost

Weaknesses

CWE-407 Inefficient Algorithmic Complexity

Affected Products

Product	Versions
MattermostMattermost	11.9.0 through 11.9.0Affected 11.8.0 through 11.8.4Affected 11.7.0 through 11.7.8Affected 10.11.0 through 10.11.22Affected 11.10.0Not affected 11.9.1Not affected 11.8.5Not affected 11.7.9Not affected 10.11.23Not affected

References

MMSA-2026-00707vendor-advisory

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