EUVD-2026-77487
GHSA-v87m-p66q-xcjg
Severity by source
AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N
Network API endpoint, no complexity; PR:H because channel/team admin credential required; S:C because system-level ABAC policy scope is violated beyond the admin's own resource scope.
Primary rating from Vendor (Mattermost).
CVSS VectorVendor: Mattermost
Lifecycle Timeline
3DescriptionCVE.org
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 fail to enforce authorization boundaries on the access control policy update endpoint which allows a channel or team administrator to detach a system-assigned ABAC parent policy via a crafted PUT /api/v4/access_control_policies request with an empty imports list.. Mattermost Advisory ID: MMSA-2026-00724
AnalysisAI
Mattermost's access control policy update endpoint fails to enforce role-based authorization boundaries, enabling a channel or team administrator to detach a system-assigned ABAC parent policy by issuing a crafted PUT /api/v4/access_control_policies request with an empty imports list. Affected are Mattermost versions 11.9.0, 11.8.x through 11.8.4, and 11.7.x through 11.7.7, per vendor advisory MMSA-2026-00724. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires an authenticated Mattermost account holding channel administrator or team administrator role - not a general user, and not requiring system administrator access (PR:H per CVSS vector). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 5.5 score with vector AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N reflects a network-reachable flaw requiring high privileges (PR:H), resulting in a scope change that produces limited confidentiality and integrity impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade Mattermost to a version beyond the affected ranges (past 11.9.0, 11.8.4, and 11.7.7 respectively) per the vendor's security advisory MMSA-2026-00724 at https://mattermost.com/security-updates. … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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