CVE-2026-16049 Missing authorization in Mattermost
Authenticated attackers can inject bot messages with arbitrary URLs into unauthorized channels via missing permission checks in the GitLab plugin.
- 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-2026-16049?
CVE-2026-16049 is a low-severity missing authorization vulnerability in Mattermost, published on 17 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mattermost Plugins versions <=11.8 10.20.11 11.5.7.0 _The Mattermost GitLab plugin fails to verify channel permissions when processing API requests with a caller-supplied_ {{post_id}}_, and fails to validate the_ {{web_url}} _parameter against the configured GitLab instance, which allows an authenticated attacker to inject bot-authored messages containing arbitrary URLs into channels they do not have access to via the_ {{createIssue}} _and_ {{attachCommentToIssue}} _API endpoints._ Mattermost Advisory ID: MMSA-2026-00673
Weakness: CWE-862
Which versions are affected by CVE-2026-16049?
How do I fix CVE-2026-16049?
No fix has been published for CVE-2026-16049 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-2026-16049 being exploited?
There is no known exploitation of CVE-2026-16049 in the wild and no public exploit code.
Sources
Also known as GHSA-vr3j-2q9w-h26r.