GNU Mailman 2.1.39, as bundled in cPanel (and WHM), allows unauthenticated attackers to read arbitrary files via ../ directory traversal at /mailman/private/mailman (aka the private archive authentication endpoint) via the username parameter. NOTE: multiple third parties report that they are unable to reproduce this, regardless of whether cPanel or WHM is used.
https://www.openwall.com/lists/oss-security/2025/04/21/6
https://github.com/cpanel/mailman2-python3