CentOS Errata and Security Advisory 2006:0600
https://rhn.redhat.com/errata/RHSA-2006-0600.html
The following updated files have been uploaded and are currently syncing to the mirrors:
i386: mailman-2.1.5.1-34.rhel4.5.i386.rpm
src: mailman-2.1.5.1-34.rhel4.5.src.rpm