A mailman security update has been released for CentOS 7.

CESA-2021:4913 Important CentOS 7 mailman Security Update

CentOS Errata and Security Advisory 2021:4913 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2021:4913

The following updated files have been uploaded and are currently
syncing to the mirrors: ( sha256sum Filename )

x86_64:
c990d11d35716ef252caf3630273bd9502a4f8556105b0ee8005c3164ce118df mailman-2.1.15-30.el7_9.2.x86_64.rpm

Source:
2ecd2a6efdc51942b93dd42a1132cdbf0499cb488c0bc85068533048df97d594 mailman-2.1.15-30.el7_9.2.src.rpm