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CVE-2026-3109 Mattermost CVE debrief

CVE-2026-3109 is a low-severity vulnerability in Mattermost Plugins versions <=11.4 10.11.11.0. The vulnerability allows an attacker to corrupt Zoom meeting state in Mattermost via replayed webhook requests due to a failure to validate webhook request timestamps. The Common Vulnerability Scoring System (CVSS) score for this vulnerability is 2.2, indicating a low severity.

Vendor
Mattermost
Product
Mattermost Server
CVSS
LOW 2.2
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 with Plugins versions <=11.4 10.11.11.0 should apply patches or mitigations to prevent potential replay attacks on Zoom meeting state.

Technical summary

The vulnerability exists in Mattermost Plugins versions <=11.4 10.11.11.0, where webhook request timestamps are not validated. This allows an attacker to corrupt Zoom meeting state via replayed webhook requests. The CVSS vector for this vulnerability is CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L.

Defensive priority

Low

Recommended defensive actions

  • Apply patches or updates to Mattermost Server to ensure Plugin versions are >= 11.4 10.11.12 or later.
  • Review and implement additional security measures to detect and prevent replay attacks on webhook requests.

Evidence notes

The vulnerability was reported via responsible disclosure to Mattermost and is tracked under Mattermost Advisory ID: MMSA-2026-00584.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-3109 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-3109

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-3109 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-3109

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.