Markdown Autolink Parsing Vulnerability in Mattermost by Mattermost
CVE-2026-12882

4.3MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
14 September 2026

What is CVE-2026-12882?

An issue exists in Mattermost where certain versions improperly handle Markdown autolinks, particularly those with unmatched trailing closing parentheses. This flaw can be exploited by authenticated users with permissions to create posts, leading to excessive CPU utilization. The result may significantly impact the server's availability, affecting other users' ability to use the service. The vulnerability is documented in the Mattermost Advisory MMSA-2026-00703.

Affected Version(s)

Mattermost 11.9.0

Mattermost 11.8.0 <= 11.8.4

Mattermost 11.7.0 <= 11.7.7

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

Adam Korczynski
.