GNU Mailman 2.1.39, as bundled in cPanel (and WHM), allows unauthenticated attackers to create lists via the /mailman/create endpoint. 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