EUVD-2026-12409
GHSA-679f-wmrg-qf57
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Primary rating from NVD.
CVSS VectorNVD
Lifecycle Timeline
4DescriptionCVE.org
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate team membership when searching channels which allows a removed team member to enumerate all public channels within a private team via the channel search API endpoint.. Mattermost Advisory ID: MMSA-2025-00568
AnalysisAI
This vulnerability is an improper access control flaw in Mattermost's channel search functionality that allows removed team members to enumerate all public channels within private teams. Affected versions include Mattermost 11.3.x through 11.3.0, 11.2.x through 11.2.2, and 10.11.x through 10.11.10. An authenticated attacker who has been removed from a team can query the channel search API endpoint to discover the complete list of public channels in that private team, resulting in information disclosure without requiring elevated privileges.
Technical ContextAI
The vulnerability stems from CWE-862 (Missing Authorization), a common authorization bypass class where the application fails to enforce proper access control checks. Specifically, Mattermost's channel search API endpoint does not adequately validate whether the authenticated user maintaining an active session still holds valid team membership before returning channel enumeration results. The affected product is identified by CPE cpe:2.3:a:mattermost:mattermost-server and impacts the server-side API layer responsible for search functionality. The root cause involves the search handler accepting queries from authenticated sessions without re-verifying team membership status, allowing stale session credentials to access resources that should be restricted to current team members only.
RemediationAI
Immediately upgrade Mattermost Server to patched versions: upgrade 10.11.x installations to 10.11.11 or later, 11.2.x installations to 11.2.3 or later, and 11.3.x installations to 11.3.1 or later, following the vendor security advisory MMSA-2025-00568. Organizations unable to patch immediately should implement network-level controls by restricting direct API access to the /api/v4/channels/search endpoint to trusted internal networks, implement robust session management practices to ensure removed team members' sessions are invalidated promptly upon team removal, and monitor API logs for unusual channel search patterns from previously-removed accounts. Additionally, consider implementing a reverse proxy that validates team membership status before forwarding requests to the Mattermost application layer as a defense-in-depth measure until patching is completed.
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Same weakness CWE-862 – Missing Authorization
View allSame technique Authentication Bypass
View allVendor StatusVendor
SUSE
Severity: Medium| Product | Status |
|---|---|
| openSUSE Leap 15.6 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Fixed |
| openSUSE Leap 15.5 | Fixed |
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External POC / Exploit Code
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