# CERT-FR Flags Mattermost Server Vulnerabilities

Published: 2026-10-21 · Severity: routine · Sectors: Technology · Not tied to an actor or CVE
Canonical: https://vorant.io/reports/d59250f4-f129-514f-8a76-9dab055f1972/cert-fr-flags-mattermost-server-vulnerabilities
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> CERT-FR advises multiple unspecified vulnerabilities in Mattermost Server allow attackers to cause an undefined security impact; patches available.

Source: cert.cyber.gouv.fr — https://www.cert.cyber.gouv.fr/avis/CERTFR-2026-AVI-1348

## 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 has issued an advisory regarding multiple vulnerabilities affecting Mattermost Server, an open-source collaboration platform. The vulnerabilities impact several version branches: 11.10.x prior to 11.10.3, 11.11.x prior to 11.11.2, and 11.7.x prior to 11.7.13. The editor (Mattermost) has not specified the precise nature of the risk or impact in the public bulletin referenced by CERT-FR.

The advisory references two Mattermost security bulletins (MMSA-2026-00772 and MMSA-2026-00783) published on 20 October 2026, which contain further technical details not reproduced in this CERT-FR notice. No information is provided regarding active exploitation in the wild. Defenders running affected Mattermost Server versions should consult the vendor's security bulletins directly and apply the available patches to update to 11.10.3, 11.11.2, or 11.7.13 or later as applicable to their deployed branch.

Given the lack of detail on exploitability, impact, or in-the-wild use, this should be treated as a standard patch-management action rather than an urgent incident response matter, pending further disclosure from the vendor.

Source reporting: https://www.cert.cyber.gouv.fr/avis/CERTFR-2026-AVI-1348

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