Cross-team file posting via reused upload metadata
Published Mar 16, 2026 · Updated Mar 16, 2026
Incorrect authorization in affected Mattermost releases allows remote authenticated users to post files across teams without permission. The post-creation path accepts file metadata uploaded under one team's upload_file permission without revalidating that permission for the destination team's channel. A guest account that can upload in one team and post in another can attach the reused file where upload_file is denied.
Summary
What happened
Incorrect authorization in affected Mattermost releases allows remote authenticated users to post files across teams without permission. The post-creation path accepts file metadata uploaded under one team's upload_file permission without revalidating that permission for the destination team's channel. A guest account that can upload in one team and post in another can attach the reused file where upload_file is denied.
The record
- CVE
- CVE-2026-4265
- Published
- Mar 16, 2026
- Updated
- Mar 16, 2026
- Vendor
- Mattermost
- Product
- Mattermost
- Classifications
- CWE-863, T1190
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Mar 16, 2026CVE publishedPublication date reported by the CVE source.
- Mar 16, 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=10.11.0 <=10.11.10
- Affected versionversion=11.2.0 <=11.2.2
- Affected versionversion=11.3.0 <=11.3.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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