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.

Human OS v1.0:
Ageing Is an Unpatched Zero-Day Vulnerability.

Remediate biological technical debt. Prime Ageing uses 95% high-purity SIRT6 activation to maintain genomic integrity and bolster systemic resilience.

Deploy the Patch

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
JSON
.