CVE-2026-10103 Missing authorization in Mattermost
Authenticated remote clusters can modify or delete local user posts in shared channels due to missing ownership verification in Mattermost.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-10103?
CVE-2026-10103 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 13 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify post ownership in the shared channel inbound sync handler, which allows an authenticated remote cluster to modify or delete posts authored by local users or other remotes via crafted sync messages referencing arbitrary post IDs in channels shared with that remote.. Mattermost Advisory ID: MMSA-2026-00689
Weakness: CWE-639
Which versions are affected by CVE-2026-10103?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-10103?
Upgrade to a fixed version.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-10103 being exploited?
There is no known exploitation of CVE-2026-10103 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-4h7j-7xp4-wp5p, MINI-837x-6946-mjhj, MINI-r64h-7h7g-h78c.