Unauthorized group subscriptions via prefix namespace matching
Published May 18, 2026 · Updated May 18, 2026
Incorrect authorization in Mattermost Plugins through 11.3.4 allows remote authenticated users to bypass group subscription whitelists. Namespace validation treats a group name that merely begins with a whitelisted namespace as valid instead of requiring an exact namespace boundary. Exploitation requires plugin-user access and an attacker-created group sharing the allowed prefix; the demonstrated consequence is subscription outside the whitelist.
Summary
What happened
Incorrect authorization in Mattermost Plugins through 11.3.4 allows remote authenticated users to bypass group subscription whitelists. Namespace validation treats a group name that merely begins with a whitelisted namespace as valid instead of requiring an exact namespace boundary. Exploitation requires plugin-user access and an attacker-created group sharing the allowed prefix; the demonstrated consequence is subscription outside the whitelist.
The record
- CVE
- CVE-2026-6342
- Published
- May 18, 2026
- Updated
- May 18, 2026
- Vendor
- Mattermost
- Product
- Mattermost
- Classifications
- CWE-863
- 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=0 <=10.13.11
- Affected versionversion=0 <=11.1.5
- Affected versionversion=0 <=11.3.4
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
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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