Participant run tampering via missing active-run checks
Published Aug 17, 2026 · Updated Aug 18, 2026
Incorrect authorization in Mattermost before 11.7.7 and 10.11.22 allows remote authenticated users to modify completed playbook runs via API requests. The Playbooks code accepted REST and GraphQL write operations on finished runs because active-run validation was missing until Mattermost centralized EnsureRunIsActive checks in middleware, handlers, and GraphQL resolvers, exempting only restore and retrospective flows. Any run participant with ordinary access to the run can alter status, checklist items, retrospective content, ownership, and participants after completion, undermining run integrity and auditability without disclosing other data or interrupting service.
Summary
What happened
Incorrect authorization in Mattermost before 11.7.7 and 10.11.22 allows remote authenticated users to modify completed playbook runs via API requests. The Playbooks code accepted REST and GraphQL write operations on finished runs because active-run validation was missing until Mattermost centralized EnsureRunIsActive checks in middleware, handlers, and GraphQL resolvers, exempting only restore and retrospective flows. Any run participant with ordinary access to the run can alter status, checklist items, retrospective content, ownership, and participants after completion, undermining run integrity and auditability without disclosing other data or interrupting service.
The record
- CVE
- CVE-2026-16046
- Published
- Aug 17, 2026
- Updated
- Aug 18, 2026
- Vendor
- Mattermost
- Product
- Mattermost
- Classifications
- CWE-863, T1565.001
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 17, 2026CVE publishedPublication date reported by the CVE source.
- Aug 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?
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- Affected versionversion=10.11.0 <=10.11.21
- Affected versionversion=11.7.0 <=11.7.6
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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