Server-Side Markdown Parser Flaw in Mattermost by Mattermost
CVE-2026-86349

4.3MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
14 September 2026

What is CVE-2026-86349?

Certain versions of Mattermost are vulnerable due to a flaw in the server-side Markdown parser that permits excessive nesting of blockquotes or list items. An authenticated user can exploit this vulnerability to craft a post that manipulates server resources, potentially leading to a denial of service through CPU exhaustion. It is critical for users of vulnerable versions to apply security updates to prevent such exploitation.

Affected Version(s)

Mattermost 11.9.0

Mattermost 11.8.0 <= 11.8.4

Mattermost 11.7.0 <= 11.7.8

References

https://mattermost.com/security-updates
vendor-advisory

CVSS V3.1

Score:
4.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

tr66net
.