Authentication Bypass in Mattermost via Action Cookie Manipulation

Executive Summary

This vulnerability affects certain versions of Mattermost (11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19) where the software fails to verify that the channel referenced in an action cookie matches the channel of the target post.

Because of this failure, an authenticated user who does not have access to a private channel can still trigger interactive post actions on posts within that private channel by using a cookie obtained from any channel they do have access to.

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Detection Guidance

Detecting this vulnerability requires checking the Mattermost server version and verifying if it falls within the affected ranges (11.7.x <= 11.7.2, 11.6.x <= 11.6.4, or 10.11.x <= 10.11.19).

• Check the Mattermost server version by running the following command on the server where Mattermost is installed: 'mattermost version'.
• Alternatively, log in to the Mattermost web interface, click on the three-dot menu in the top-left corner, and navigate to 'About Mattermost' to view the version.

If the version matches any of the affected ranges, the system is vulnerable. No specific network detection commands are provided for this vulnerability, as it is related to server-side logic and authentication.

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Impact Analysis

This vulnerability can allow an authenticated user to perform actions on posts in private channels they are not authorized to access.

While it does not allow reading the content of the private channel posts, it can impact the integrity of the channel by enabling unauthorized interactive post actions.

According to the CVSS score (6.5), the impact is considered to be of medium severity with high impact on integrity but no impact on confidentiality or availability.

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Compliance Impact

This vulnerability could impact compliance with standards and regulations like GDPR and HIPAA due to its potential to expose or manipulate sensitive information without proper authorization.

Under GDPR, unauthorized access to private channels containing personal data could constitute a breach of data protection principles, particularly if the exposed data includes personally identifiable information (PII). This may lead to non-compliance with GDPR's requirements for data confidentiality and integrity.

For HIPAA, if the affected Mattermost instance is used in a healthcare setting and private channels contain protected health information (PHI), this vulnerability could result in unauthorized access to PHI. This violates HIPAA's Privacy and Security Rules, which mandate strict access controls and safeguards for PHI.

• GDPR: Non-compliance risk due to unauthorized access to personal data in private channels.
• HIPAA: Potential violation if PHI is exposed or manipulated without proper authorization.

Organizations using Mattermost in regulated environments should assess the impact of this vulnerability on their compliance posture and apply patches or mitigations promptly to avoid regulatory penalties.

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Mitigation Strategies

The following steps can be taken to mitigate this vulnerability:

• Upgrade the Mattermost server to the latest patched version as soon as possible. Refer to the official Mattermost security updates page for the fixed versions.
• If upgrading is not immediately possible, restrict access to private channels to minimize exposure. Ensure only authorized users have access to sensitive channels.
• Monitor Mattermost logs for unusual activity, such as authenticated users attempting to trigger actions on posts in channels they do not have access to.

For the latest updates and patches, visit the Mattermost security updates page (Resource 1).

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