Overview
CVE-2025-41436 describes a vulnerability in Mattermost versions prior to 11.0. This flaw allows regular users to bypass intended access controls and view content within archived channels, even if they should not have permission. The vulnerability stems from improper enforcement of the “Allow users to view archived channels” setting when accessing content via the “Open in Channel” functionality from followed threads.
Technical Details
The core issue resides in the insufficient validation of user permissions when accessing archived channel content through the “Open in Channel” feature linked from followed threads. While the “Allow users to view archived channels” setting is intended to restrict access, the implementation failed to apply this restriction consistently across all access paths. Specifically, the link from a followed thread allowed users to circumvent the intended access control, effectively bypassing the restrictions on archived content.
CVSS Analysis
The vulnerability has been assigned a CVSS score of 3.1, indicating a LOW severity. This is primarily due to the need for a user to already be following a thread within the archived channel to exploit the vulnerability. The CVSS vector string is likely something similar to: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N, indicating Network attack vector, Low attack complexity, Low privileges required, User interaction required, Unchanged scope, Low Confidentiality impact, No Integrity impact, and No Availability impact.
Possible Impact
While rated as low severity, the impact of this vulnerability should not be entirely dismissed. The potential impact includes:
- Information Disclosure: Unauthorized access to potentially sensitive information stored within archived channels.
- Compromised Confidentiality: While the scope is limited, it could lead to exposure of confidential discussions or files.
- Compliance Issues: Depending on the nature of the data within the archived channels and relevant regulations (e.g., GDPR, HIPAA), this unauthorized access could lead to compliance violations.
Mitigation and Patch Steps
The primary mitigation step is to upgrade your Mattermost server to version 11.0 or later. This version includes the necessary fix to properly enforce the “Allow users to view archived channels” setting and prevent unauthorized access. Refer to the official Mattermost upgrade documentation for detailed instructions on performing the upgrade.
- Backup your Mattermost data: Before initiating the upgrade, create a full backup of your Mattermost database and file storage.
- Review the Mattermost upgrade guide: Consult the official Mattermost documentation for upgrade instructions specific to your current version.
- Test the upgrade in a staging environment: If possible, test the upgrade in a staging environment before applying it to your production system.
- Apply the upgrade: Follow the documented procedure to upgrade your Mattermost server to version 11.0 or later.
- Verify the fix: After the upgrade, verify that the “Allow users to view archived channels” setting is functioning correctly and preventing unauthorized access to archived channel content via the “Open in Channel” feature.
