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CERT-FR flags Mattermost Server security bypass flaw

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CERT-FR warns of a security policy bypass vulnerability in Mattermost Server affecting versions before 11.7.11, 11.8.6, and 11.9.2.

Sourcecert.cyber.gouv.fr — open the original

What to check

Applies to
The 1 CVE named below. Whether you run an affected version is not assessed: check the versions the source lists.
Exploitation
No exploitation in the wild and no public exploit is recorded for the CVEs named.

CERT-FR issued an advisory regarding a vulnerability in Mattermost Server that allows an attacker to bypass the application's security policy. The affected versions are 11.7.x prior to 11.7.11, 11.8.x prior to 11.8.6, and 11.9.x prior to 11.9.2. The issue is tracked as CVE-2026-93851 and was documented by Mattermost in its own security bulletin MMSA-2026-00742, published October 28, 2026.

No details on exploitation in the wild are provided in this advisory. Defenders running Mattermost Server should consult the vendor's security bulletin and upgrade to the patched versions (11.7.11, 11.8.6, or 11.9.2 or later) to remediate the security policy bypass.

Mentioned in this report

Vulnerabilities CVE-2026-93851

Related reporting

Source reporting: https://www.cert.cyber.gouv.fr/avis/CERTFR-2026-AVI-1409

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