CVE-2025-9079: Path Traversal in Mattermost Server

The core of this vulnerability lies in the improper handling of user-supplied input, allowing an attacker to manipulate file paths and access files outside of the intended directory. A successful exploit could enable an attacker to read configuration files, source code, or even sensitive user data stored on the server. The blast radius extends to any data accessible by the Mattermost Server process, and the potential for lateral movement depends on the server's overall security posture and access controls. While no direct precedent is immediately obvious, path traversal vulnerabilities often lead to information disclosure and privilege escalation.

1. Reserved2025-08-15
2. Published2025-09-24
3. Modified2026-03-03
4. EPSS updated2026-03-23

The primary mitigation is to immediately upgrade Mattermost Server to version 9.11.18+incompatible or later. If upgrading is not immediately feasible, consider implementing a Web Application Firewall (WAF) with rules to filter out malicious path traversal attempts. Specifically, look for patterns involving .. sequences in file paths. Review and restrict file permissions on the Mattermost Server installation directory to limit the potential damage from a successful exploit. Monitor Mattermost server logs for unusual file access attempts. After upgrade, confirm by attempting to access a known restricted file via a web request and verifying that access is denied.