Multiple vulnerabilities in Mattermost products (May 22, 2026)

unknownCVE-2026-6517 CVE-2026-9162 CVE-2026-5139 CVE-2026-8074 CVE-2026-8823 CVE-2026-6062

Multiple vulnerabilities have been discovered in Mattermost products. They allow an attacker to cause security policy bypass and an unspecified security issue by the editor.

CSIRTS triage

vendor: Mattermost product: Mattermost Authentication bypassOther

What: Multiple vulnerabilities in Mattermost products allow attackers to bypass security policies and cause unspecified security issues through the editor.
Who is affected: All Mattermost product deployments are affected; specific versions are not stated.
Urgency: Moderate urgency; security policy bypass is serious but no active exploitation reported.
Action: Check Mattermost security advisory page for affected versions and apply available patches.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: CERT-FR Avis de sécurité (FR · national-cert · site)
Severity: unknown
Published: 2026-05-22
Exploitation: Not in CISA KEV at last sync
Language: Machine-translated to English — verify against the original

Original advisory: https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-0632/

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-65170.19% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 9% of all EPSS-scored CVEs.
Low exploitation riskCVE-2026-91620.33% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 26% of all EPSS-scored CVEs.
Low exploitation riskCVE-2026-51390.29% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 21% of all EPSS-scored CVEs.
Low exploitation riskCVE-2026-80740.32% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 25% of all EPSS-scored CVEs.
Low exploitation riskCVE-2026-88230.32% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 25% of all EPSS-scored CVEs.
Low exploitation riskCVE-2026-60620.24% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 15% of all EPSS-scored CVEs.
Low exploitation riskCVE-2026-66730.30% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 23% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-6517	coverage & exploitation status	NVD · CVE.org
CVE-2026-9162	coverage & exploitation status	NVD · CVE.org
CVE-2026-5139	coverage & exploitation status	NVD · CVE.org
CVE-2026-8074	coverage & exploitation status	NVD · CVE.org
CVE-2026-8823	coverage & exploitation status	NVD · CVE.org
CVE-2026-6062	coverage & exploitation status	NVD · CVE.org
CVE-2026-6673	coverage & exploitation status	NVD · CVE.org

Recent advisories for Mattermost products

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

unknownMultiple vulnerabilities in Mattermost products (August 14, 2026)cert-fr-avis · 2026-08-14
unknownMultiple vulnerabilities in Mattermost products (June 15, 2026)cert-fr-avis · 2026-06-15
unknownMultiple vulnerabilities in Mattermost products (May 29, 2026)cert-fr-avis · 2026-05-29
unknownMultiple vulnerabilities in Mattermost products (May 19, 2026)cert-fr-avis · 2026-05-19