Cyber Resilience

CVE-2025-53971

Access Control in Mattermost Server 9.11.0 – 9.11.18

Published
21 August 2025
Modified
17 June 2026
Patch / advisory
CVSS Score v3.1 3.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N
EPSS Score 0.0020 11th percentile
Risk Priority 21 floored blend · peak EPSS

Summary

CVE-2025-53971 is a low-severity Incorrect Authorization (CWE-863) vulnerability in Mattermost Mattermost Server. Its CVSS base score is 3.8 (Low).

Operationally, ranked at the 11th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-24 (Access Control Decisions) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

EU & UK References

Vulnerability Data

Mattermost versions 10.5.x <= 10.5.8, 9.11.x <= 9.11.17 fail to properly validate authorization for team scheme role modifications which allows Team Admins to demote Team Members to Guests via the PUT /api/v4/teams/team-id/members/user-id/schemeRoles API endpoint.

CWE(s)

Related Threats

CVEs Like This One

CVE-2026-6343Same product: Mattermost Mattermost Server
CVE-2026-2462Same product: Mattermost Mattermost Server
CVE-2025-11776Same product: Mattermost Mattermost Server
CVE-2024-9155Same product: Mattermost Mattermost Server
CVE-2026-10106Same product: Mattermost Mattermost Server
CVE-2026-6739Same product: Mattermost Mattermost Server
CVE-2024-42000Same product: Mattermost Mattermost Server
CVE-2025-24920Same product: Mattermost Mattermost Server
CVE-2025-3228Same product: Mattermost Mattermost Server
CVE-2026-6342Same product: Mattermost Mattermost Server

Affected Assets

mattermost
mattermost server
9.11.0 — 9.11.18 · 10.5.0 — 10.5.9

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • AC-3 Access Enforcement
  • AC-6 Least Privilege
  • AC-24 Access Control Decisions
Detect
Catch it (NIST detect / respond)

Harden
Shrink the surface (DISA STIG)
  • 5 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)

Mitigating Controls (NIST 800-53 r5) AI

prevent

Directly enforces authorization checks on the PUT /api/v4/teams/.../schemeRoles endpoint so Team Admins cannot modify roles they are not permitted to change.

prevent

Restricts Team Admin privileges to the minimum required, eliminating the ability to demote members to Guests via scheme-role modifications.

prevent

Ensures access-control decisions for role changes are made by a centralized, validated mechanism rather than trusting client-supplied team-admin claims.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-05 mostly match
prevents

Defining, enforcing, and reviewing access authorizations and least privilege directly prevents incorrect authorization checks.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

prevents

Requiring consistency between access rights and classification plus formal approval steps ensures that the authorization logic correctly distinguishes between entities that should and should not be granted access.

prevents

Enforcing policy-driven approval and role-change reviews stops incorrect or stale authorization decisions from remaining in effect after job changes or terminations.

prevents

By tying access rights to identity, device, location and classification, the control reduces the likelihood that an authorization decision will be based on an incorrect or bypassed policy.

References