Mattermost GitLab Plugin <=11.8: Authenticated Injection via API (CVE-2026-16049)
CVE-2026-16049 Published on August 17, 2026
_GitLab Plugin allows cross-channel post injection and phishing via missing channel permission checks in issue API endpoints_
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
Vulnerability Analysis
CVE-2026-16049 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality, a small impact on integrity and availability.
Weakness Type
What is an AuthZ Vulnerability?
The software does not perform an authorization check when an actor attempts to access a resource or perform an action.
CVE-2026-16049 has been classified to as an AuthZ vulnerability or weakness.
Products Associated with CVE-2026-16049
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Affected Versions
Mattermost:- Before and including 10.20.11 is affected.
- Before and including 11.5.7 is affected.
- Version 11.9.0 is unaffected.
- Version 10.11.21 is unaffected.
- Version 11.7.6 is unaffected.