[UPDATE] [medium] Mattermost Server: Multiple vulnerabilities

mediumCVE-2026-13426 CVE-2026-9597

An attacker can exploit multiple vulnerabilities in Mattermost Server to manipulate data, bypass security measures, or conduct other unspecified attacks.

CSIRTS triage

vendor: Mattermost product: ServerOther

What: Multiple vulnerabilities can be exploited to manipulate data and bypass security measures.
Who is affected: Users of Mattermost Server are affected.
Urgency: Remediation is medium urgency as the specific impacts are unspecified.
Action: Update Mattermost Server to the latest version to mitigate these vulnerabilities.

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

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Details

Source: CERT-Bund (BSI) Security Advisories (DE · national-cert · site)
Severity: medium
Published: 2026-07-28
Exploitation: Not in CISA KEV at last sync
Language: Machine-translated to English — verify against the original

Original advisory: https://wid.cert-bund.de/portal/wid/securityadvisory?name=WID-SEC-2026-2107

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-2026-134260.20% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 10% of all scored CVEs.
Low exploitation riskCVE-2026-95970.14% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 4% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-13426	coverage & exploitation status	NVD · CVE.org
CVE-2026-9597	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for Mattermost Server

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.

mediumCVE-2026-10600: Mattermost versions 11.8.x <= 11.8.0, 11.7.x <= 11.7.3, 11.6.x <= 11.6.5, 10.11.x <= 10.11.20 …nvd · 2026-07-27
unknownMultiple vulnerabilities in Mattermost Server (July 20, 2026)cert-fr-avis · 2026-07-20
mediumCVE-2026-9602: Mattermost Desktop App versions <=6.2 6.0.2 5.6.13.0 fail to validate payloads sent from the Ma…nvd · 2026-07-17
unknownMultiple vulnerabilities in Mattermost Server (June 29, 2026)cert-fr-avis · 2026-06-29
mediumCVE-2026-9699: Mattermost Plugins versions <=11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses fr…nvd · 2026-06-26