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PatchSiren cyber security CVE debrief

CVE-2026-7387 Mattermost CVE debrief

CVE-2026-7387 is a high-severity vulnerability in Mattermost that allows for authorization bypass. The vulnerability affects Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, and 10.11.x <= 10.11.16. An attacker with group-link permissions can escalate themselves and group members to team or channel admin via crafted API requests. The vulnerability has a CVSS score of 8.8 and is classified as HIGH.

Vendor
Mattermost
Product
Unknown
CVSS
HIGH 8.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-12
Original CVE updated
2026-06-18
Advisory published
2026-06-12
Advisory updated
2026-06-18

Who should care

Users of Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, and 10.11.x <= 10.11.16 should be aware of this vulnerability and take steps to mitigate it.

Technical summary

Mattermost fails to require role-management authorization when setting the scheme_admin flag on group syncable link and patch endpoints. This allows a user with group-link permissions to escalate themselves and group members to team or channel admin via crafted API requests.

Defensive priority

HIGH

Recommended defensive actions

  • Upgrade to a version of Mattermost that is not affected by this vulnerability.
  • Restrict group-link permissions to only those who need them.
  • Monitor for suspicious activity on your Mattermost instance.

Evidence notes

The vulnerability was reported to Mattermost via responsible disclosure and has been publicly disclosed.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-7387 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-7387

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-7387 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-7387

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.