CVE-2025-13321: 
JavaScript vulnerability analysis and mitigation

CVE-2025-13321 is a log information disclosure vulnerability in the Mattermost Desktop App affecting all versions prior to 6.0.0. The application fails to sanitize sensitive information written to its logs and does not clear data when a server is deleted, allowing a local attacker with low privileges to read potentially sensitive information from application log files. It was published on December 17, 2025, with a patch available in version 6.0.0. The vulnerability carries a CVSS v3.1 base score of 3.3 (Low) (GitHub Advisory, Mattermost Security).

The root cause is classified as CWE-532 (Insertion of Sensitive Information into Log File): the Mattermost Desktop App writes sensitive data to its application logs without adequate sanitization, and fails to purge this data when a connected server is removed by the user. An attacker with local, low-privileged access to the affected system can read the application log files directly from disk to extract the retained sensitive information. No network access or user interaction is required, and exploitation is straightforward given local filesystem access (GitHub Advisory, Mattermost Security).

Successful exploitation allows a local attacker to read Mattermost Desktop App log files and potentially extract sensitive information such as communication details, authentication tokens, or other private data that was not properly sanitized before being written to logs. The impact is limited to confidentiality (no integrity or availability impact), and exploitation requires existing local access to the user's system. There is no evidence of lateral movement potential beyond the information exposed in the logs (GitHub Advisory).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation at this time. The EPSS score is approximately 0.012–0.017%, placing it in the 4th percentile for exploitation likelihood within 30 days. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported (GitHub Advisory).

1. Local Access: Gain low-privileged local access to a system where Mattermost Desktop App version prior to 6.0.0 is installed.
2. Locate Log Files: Navigate to the Mattermost Desktop App log directory (typically within the user's application data folder, e.g., %APPDATA%\Mattermost\logs on Windows or ~/.config/Mattermost/logs on Linux/macOS).
3. Read Log Files: Open or copy the application log files (e.g., mattermost.log) and search for sensitive information such as server URLs, authentication tokens, or user data that was not sanitized before being written.
4. Extract Residual Data: If a server was previously deleted by the user, check logs for data that should have been cleared upon server deletion but was retained due to the incomplete data-clearing logic (GitHub Advisory).

• File System: Unauthorized access or copying of Mattermost Desktop App log files from user application data directories (e.g., %APPDATA%\Mattermost\logs\ on Windows, ~/.config/Mattermost/logs/ on Linux/macOS).
• Logs: OS-level audit logs showing unexpected read access to Mattermost log files by processes or users other than the Mattermost Desktop App or the owning user.
• Process: Unusual processes (e.g., command-line tools like cat, type, grep, or scripting engines) accessing Mattermost log file paths.

Upgrade the Mattermost Desktop App to version 6.0.0 or later, which includes fixes for log sanitization and proper data clearing on server deletion. The fix is available via direct download from the Mattermost Desktop repository; note that at the time of publication, the patched version had not been uploaded to the npm registry. As interim measures, restrict local user access to Mattermost log directories, implement full disk encryption, and apply the principle of least privilege for user accounts (Mattermost Security, GitHub Advisory).