Authentication Bypass in Mattermost Playbook Metrics

Executive Summary

CVE-2026-6541 is a vulnerability in Mattermost versions 11.7.x <= 11.7.1, 11.6.x <= 11.6.4, and 10.11.x <= 10.11.19. The issue occurs because the software fails to restrict metric configuration changes to the playbook being saved.

An authenticated user with team access can exploit this vulnerability by sending a crafted import or update request containing a foreign metric ID. This allows the attacker to alter another user’s playbook metric settings without proper authorization.

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Detection Guidance

Detecting this vulnerability requires checking for unauthorized changes to playbook metric settings in Mattermost. Since the vulnerability allows an authenticated user to alter another user's playbook metric settings via crafted requests, you can monitor for unusual activity in the following ways:

• Review Mattermost server logs for unexpected or frequent import/update requests related to playbook metrics. Look for requests containing foreign metric IDs or unusual patterns in metric configuration changes.
• Check the Mattermost database or configuration files for discrepancies in playbook metric settings, particularly if metrics appear to have been modified by users who should not have access.
• Use network monitoring tools to inspect HTTP requests to the Mattermost server, focusing on endpoints related to playbook imports or updates. Look for requests with suspicious payloads or unexpected metric IDs.

There are no specific commands provided in the context for direct detection, but you can use general logging and monitoring tools like grep, awk, or SIEM solutions to analyze logs for anomalous behavior. For example:

• grep -i 'playbook.*metric.*update' /var/log/mattermost/mattermost.log to search for playbook metric update events in logs.
• Use a SIEM tool to set up alerts for unusual playbook metric modifications, such as changes made by non-admin users or outside of expected workflows.

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Impact Analysis

If you are using an affected version of Mattermost, this vulnerability could impact you in the following ways:

• Unauthorized changes to playbook metric settings: An attacker with team access could modify another user’s playbook metrics, leading to incorrect or manipulated data.
• Potential data integrity issues: Altered metrics could result in misleading analytics or operational decisions based on compromised data.
• Exploitation requires authenticated access: The attacker must have valid credentials and team access to exploit this vulnerability.

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Compliance Impact

This vulnerability may impact compliance with common standards and regulations in the following ways:

• GDPR: If the affected playbook metrics contain or influence personal data processing, unauthorized modifications could lead to non-compliance with GDPR’s data integrity and confidentiality requirements (Article 5(1)(f)).
• HIPAA: If the playbook metrics involve protected health information (PHI), unauthorized changes could violate HIPAA’s Security Rule, which mandates safeguards for electronic PHI (ePHI) integrity and access controls.
• General security standards: The vulnerability represents a failure in access control (e.g., ISO 27001, NIST SP 800-53), which could affect compliance with frameworks requiring strict authorization mechanisms.

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Mitigation Strategies

To mitigate this vulnerability, follow these immediate steps:

• Upgrade Mattermost to a patched version. The affected versions are 11.7.x <= 11.7.1, 11.6.x <= 11.6.4, and 10.11.x <= 10.11.19. Apply the latest security updates provided by Mattermost to resolve the issue.
• Restrict access to playbook metric configuration features to trusted users only. Ensure that only authorized personnel can import or update playbook metrics.
• Monitor and audit playbook metric changes regularly to detect any unauthorized modifications. Implement logging for all metric-related actions and review logs for suspicious activity.
• Review and enforce least-privilege access controls for Mattermost users to minimize the risk of exploitation. Limit permissions for users who do not require access to playbook metrics.
• Subscribe to Mattermost security bulletins to stay informed about future updates and vulnerabilities. Visit https://mattermost.com/security-updates for the latest security advisories.

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