EUVD-2026-16245Severity 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 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to apply view restrictions when retrieving group member IDs, which allows authenticated guest users to enumerate user IDs outside their allowed visibility scope via the group retrieval endpoint.. Mattermost Advisory ID: MMSA-2026-00594
AnalysisAI
Mattermost versions 11.2.x through 11.4.x fail to enforce view restrictions on group member endpoints, allowing authenticated guest users to enumerate user IDs beyond their authorized visibility scope. This authorization bypass requires valid credentials but enables attackers to discover internal user information through the group retrieval API. No patch is currently available for affected versions.
Technical ContextAI
The vulnerability stems from improper access control (CWE-863: Improper Authorization) in Mattermost's group member endpoint. When guest users-authenticated accounts with restricted permissions-query the group retrieval API, the application fails to apply visibility filtering rules that ordinarily restrict which users appear in results based on configured scopes and group membership. Mattermost (cpe:2.3:a:mattermost:mattermost) is a self-hosted, open-source team collaboration platform that manages user visibility through role-based access control (RBAC) and organizational boundaries. The flaw allows these controls to be bypassed specifically for group member ID enumeration, exposing internal user identifiers that could be used for downstream reconnaissance or targeted attacks.
RemediationAI
Upgrade affected Mattermost instances to patched releases immediately. Users on version 10.11.x should update to 10.11.11 or later; those on 11.2.x should upgrade to 11.2.3 or later; 11.3.x users should move to 11.3.2 or later; and 11.4.x users should update to 11.4.1 or later (consult the Mattermost security advisory at https://mattermost.com/security-updates for exact patched versions). As an interim control, restrict guest-account creation and assignment to non-sensitive groups, and monitor API logs for unusual group-member enumeration requests. Network-level access controls limiting group endpoint exposure to trusted IP ranges can reduce attack surface until patching is completed.
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Same weakness CWE-863 – Incorrect Authorization
View allSame technique Authentication Bypass
View allVendor StatusVendor
Debian
Bug #823556| Release | Status | Fixed Version | Urgency |
|---|---|---|---|
| open | - | - |
SUSE
Severity: Moderate| Product | Status |
|---|---|
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Affected |
| openSUSE Leap 15.5 | Affected |
| openSUSE Leap 15.6 | Affected |
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External POC / Exploit Code
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