CentOS Errata and Security Advisory 2007:0022
https://rhn.redhat.com/errata/RHSA-2007-0022.html
The following updated files have been uploaded and are currently syncing to the mirrors:
x86_64: squirrelmail-1.4.8-4.el4.noarch.rpm
src: squirrelmail-1.4.8-4.el4.src.rpm