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CERT-FR flags multiple Mattermost Server flaws

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CERT-FR advises patching multiple unspecified vulnerabilities in Mattermost Server affecting several 11.x branches, with no exploitation details or CVE IDs disclosed.

Sourcecert.ssi.gouv.fr — open the original

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CERT-FR published an advisory referencing fifteen Mattermost security bulletins (MMSA-2026 series) issued by the vendor on 19 October 2026. The advisory does not specify the nature of the vulnerabilities, stating only that they allow an attacker to cause an unspecified security issue. No CVE identifiers, exploitation details, or technical root causes are provided in this CERT-FR bulletin.

Affected systems include Mattermost Server versions 11.7.x prior to 11.7.12, 11.8.x prior to 11.8.6, 11.10.x prior to 11.10.3, and 11.11.x prior to 11.11.2. Organizations running Mattermost Server should consult the vendor's security-updates page for the full list of MMSA bulletins and apply the corresponding patched versions. No indication of active exploitation is given in this advisory.

Defenders operating Mattermost instances should prioritize upgrading to the fixed versions noted above and review the referenced MMSA bulletins directly from Mattermost for further technical detail, as CERT-FR's summary does not elaborate on impact severity or attack vectors.

Related reporting

Source reporting: https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-1344

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