CentOS Errata and Security Advisory 2006:0283
https://rhn.redhat.com/errata/RHSA-2006-0283.html
The following updated files have been uploaded and are currently syncing to the mirrors:
i386: squirrelmail-1.4.6-5.el4.centos4.noarch.rpm
src: squirrelmail-1.4.6-5.el4.centos4.src.rpm