Denial of Service Vulnerability in Mattermost Server
CVE-2026-26233

4.3MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
25 March 2026

What is CVE-2026-26233?

Certain versions of Mattermost Server are vulnerable to a denial of service attack due to inadequate rate limiting on login requests. This flaw allows unauthenticated remote attackers to launch an HTTP/2 single packet attack, overwhelming the server with over 100 parallel login requests. As a result, the server may crash or restart, disrupting services and potentially affecting all users. Users of Mattermost are advised to update to secure versions to mitigate this risk.

Affected Version(s)

Mattermost 11.4.0

Mattermost 11.3.0 <= 11.3.1

Mattermost 11.2.0 <= 11.2.3

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

Axel Larsson & Jakob Ristner
.