# CERT-FR Flags Mattermost Server Vulnerability

Published: 2026-10-19 · Severity: routine · Sectors: Technology · Not tied to an actor or CVE
Canonical: https://vorant.io/reports/5e2052e1-0056-5cee-90d5-13fb63843739/cert-fr-flags-mattermost-server-vulnerability
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> CERT-FR advises a security flaw in Mattermost Server 11.7.x before 11.7.12, with impact unspecified by the vendor; patch available.

Source: cert.ssi.gouv.fr — https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-1338

## What to check

- Applies to: Not tied to a specific actor, malware or CVE, only to the sectors it covers, so it may be general reporting. Check the source before acting on it. Whether it concerns you is not assessed.

CERT-FR issued an advisory regarding a vulnerability affecting Mattermost Server versions 11.7.x prior to 11.7.12. The vendor, Mattermost, has not publicly specified the exact nature or impact of the security issue, only confirming via its own security bulletin (MMSA-2026-00709, dated October 16, 2026) that a fix is available. No details on exploitability, attack vector, or whether the flaw is being exploited in the wild were provided in either the CERT-FR advisory or the referenced vendor documentation.

Defenders running Mattermost Server should identify any instances on the affected 11.7.x branch prior to version 11.7.12 and apply the vendor's patch as described in the official security update documentation. Given the lack of technical detail, organizations should monitor the vendor's security guide for further clarification and treat this as a routine patch-management action until more information becomes available.

Source reporting: https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-1338

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