Private thread disclosure via unchecked rewrite context
Published May 18, 2026 · Updated May 18, 2026
Missing authorization in Mattermost 11.5.0 through 11.5.1 allows remote authenticated users to read private thread content. The buildThreadContextForRewrite function passed an attacker-controlled root_id to GetPostThread without first calling GetPostIfAuthorized on the anchor post. Any authenticated account able to call the AI rewrite endpoint could reference an unreadable private channel or direct message, exposing up to ten context posts to the rewrite workflow.
Summary
What happened
Missing authorization in Mattermost 11.5.0 through 11.5.1 allows remote authenticated users to read private thread content. The buildThreadContextForRewrite function passed an attacker-controlled root_id to GetPostThread without first calling GetPostIfAuthorized on the anchor post. Any authenticated account able to call the AI rewrite endpoint could reference an unreadable private channel or direct message, exposing up to ten context posts to the rewrite workflow.
The record
- CVE
- CVE-2026-5163
- Published
- May 18, 2026
- Updated
- May 18, 2026
- Vendor
- Mattermost
- Product
- Mattermost
- Classifications
- CWE-862, T1213
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- May 18, 2026CVE publishedPublication date reported by the CVE source.
- May 18, 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=11.5.0 <=11.5.1
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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