CVE-2026-15754 Missing per-channel team-scope check in ABAC access control policy unassign allows cross-team policy removal
Authenticated team admins can remove access control policies from channels belonging to other teams due to missing scope validation.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-15754?
CVE-2026-15754 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 17 Aug 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Official description
Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC (attribute-based access control) policy assignments from channels outside their team via the policy unassign API after a channel has been moved to another team.. Mattermost Advisory ID: MMSA-2026-00718
Weakness: CWE-863
Which versions are affected by CVE-2026-15754?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-15754?
No fix has been published for CVE-2026-15754 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-15754 being exploited?
There is no known exploitation of CVE-2026-15754 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Mattermost Server
- CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers
- CVE-2025-12421 Account Takeover via Code Exchange Endpoint
- CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User
- CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards
- CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive
Sources
Also known as GHSA-mg83-f953-3vq5.