Cross-channel phishing via unchecked post_id and web_url
Published Aug 17, 2026 · Updated Aug 17, 2026
Missing authorization in the Mattermost GitLab plugin lets remote authenticated users inject bot-authored links into channels they cannot access. In the vulnerable issue APIs, createIssue and attachCommentToIssue trust a caller-supplied post_id without confirming posting rights in the referenced channel, and attachCommentToIssue also accepted a caller-supplied web_url until the fix added host and path checks against the configured GitLab instance. Public records list affected releases up to 11.8, 10.20.11, and 11.5.7; exploitation requires any authenticated account that can reach those endpoints, and published detail does not describe broader state changes beyond unauthorized bot-authored posts and link delivery.
Summary
What happened
Missing authorization in the Mattermost GitLab plugin lets remote authenticated users inject bot-authored links into channels they cannot access. In the vulnerable issue APIs, createIssue and attachCommentToIssue trust a caller-supplied post_id without confirming posting rights in the referenced channel, and attachCommentToIssue also accepted a caller-supplied web_url until the fix added host and path checks against the configured GitLab instance. Public records list affected releases up to 11.8, 10.20.11, and 11.5.7; exploitation requires any authenticated account that can reach those endpoints, and published detail does not describe broader state changes beyond unauthorized bot-authored posts and link delivery.
The record
- CVE
- CVE-2026-16049
- Published
- Aug 17, 2026
- Updated
- Aug 17, 2026
- Vendor
- Mattermost
- Product
- Mattermost
- Classifications
- CWE-862, T1566.002
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 17, 2026CVE publishedPublication date reported by the CVE source.
- Aug 17, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <=10.20.11
- Affected versionversion=0 <=11.5.7
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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