Mattermost versions 11 are affected by an information disclosure vulnerability that requires high-level authentication to exploit.

The flaw is an instance of CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). It requires an attacker to possess high privileges (PR:H) to perform the unauthorized data access.

The vulnerability carries a CVSS score of 7.6 (High), reflecting a significant risk of data exposure. While the requirement for high-level administrative privileges limits the attack surface, the potential for unauthorized access to sensitive organizational communications could lead to severe reputational damage and the compromise of confidential internal data.

Immediate Action: Update Mattermost instances to versions 11.6.0, 11.5.2, 10.11.14, or 11.4.4.

Proactive Monitoring: Audit administrative access logs for unusual data export or query patterns that deviate from standard operational behavior.

Compensating Controls: Ensure strict adherence to the Principle of Least Privilege (PoLP) to minimize the number of accounts possessing the high-level permissions required to trigger this vulnerability.

Public Exploit Available: Unknown.

Given the High severity rating, organizations should prioritize patching affected Mattermost server installations. Administrators must verify their current version strings against the provided list and apply the identified security updates during the next maintenance window to prevent potential unauthorized data access.