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CVE-2026-93851 - Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to validate the target post ID in the Age

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to validate the target post ID in the Agents plugin's mention reminder component, which allows an authenticated user who can post in a channel visible to a system administrator to cause the administrator's browser to send an unintended API request, resulting in replacement of an installed plugin and code execution on the server, via a crafted post containing a forged mention reminder that the administrator clicks. Mattermost Advisory ID: MMSA-2026-00742
HIGH
Severity & confidence
Source severityhigh
Platform severityhigh
Confidencehigh
Exploitationunknown
CVSS8.0
Affected
Reporting sources (1)
NIST NVD - National Vulnerability Database
Open source โ†—
Timeline & provenance
Published2026-10-28T22:17:17
Last updated2026-10-31T22:08:09
Ingested2026-10-31T11:24:29
FreshnessNEAR-REAL-TIME
Threat typevulnerability
Recommended action
No recommended action published with this item - review the original source.
Next steps
  1. Identify affected systems in your environment.
  2. Apply the vendor patch or mitigation guidance.
  3. Review logs for indicators described in the advisory.
  4. Follow the affected vendor/product to track updates.
Confidence explanation
Reported by a government or cert-grade source (CISA, NCSC, NVD, ENISA, MSRC).
Source type: standards ยท Original: NIST NVD - National Vulnerability Database