CVE-2026-18560 Information disclosure in Mattermost
Authenticated users can infer a post's quarantined status via API due to improper authorization order, exposing sensitive moderation metadata.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-18560?
CVE-2026-18560 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 16 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate user’s permissions before other validations which allows non-content reviewers to infer a post’s flagged status via direct API call.. Mattermost Advisory ID: MMSA-2026-00754
Weakness: CWE-203
Which versions are affected by CVE-2026-18560?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-18560?
No fix has been published for CVE-2026-18560 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-18560 being exploited?
There is no known exploitation of CVE-2026-18560 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-3m39-x8xr-762f.