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CVE-2026-3116 Mattermost CVE debrief

CVE-2026-3116 is a vulnerability in Mattermost Plugins versions <=11.4, 11.0.4, 11.1.3, 11.3.2, 10.11.11.0. The vulnerability fails to validate incoming request size, allowing an authenticated attacker to cause service disruption via the webhook endpoint. The vulnerability has a CVSS score of 4.9 and a severity of MEDIUM.

Vendor
Mattermost
Product
Mattermost Server
CVSS
MEDIUM 4.9
CISA KEV
Not listed in stored evidence
Original CVE published
2026-03-26
Original CVE updated
2026-06-08
Advisory published
2026-03-26
Advisory updated
2026-06-08

Who should care

Users of Mattermost Server versions 10.11.0 to 10.11.12, 11.2.0 to 11.2.4, 11.3.0 to 11.3.2, and 11.4.0 to 11.4.1 should apply patches or mitigations.

Technical summary

The vulnerability is caused by a lack of validation for incoming request sizes in Mattermost Plugins. This allows an authenticated attacker to cause a denial of service (DoS) via the webhook endpoint.

Defensive priority

MEDIUM

Recommended defensive actions

  • Apply patches or updates to Mattermost Server versions 10.11.0 to 10.11.12, 11.2.0 to 11.2.4, 11.3.0 to 11.3.2, and 11.4.0 to 11.4.1.
  • Refer to [ref-4](https://mattermost.com/security-updates) for vendor advisory and mitigation guidance.

Evidence notes

The CVE was published on [cvePublishedAt](https://www.cve.org/CVERecord?id=CVE-2026-3116) and last modified on [cveModifiedAt](https://nvd.nist.gov/vuln/detail/CVE-2026-3116).

Official resources

CVE-2026-3116 was disclosed by Mattermost on [cvePublishedAt].