The following errata for CentOS-2 have been built and uploaded to the centos mirror:

RHSA-2008:0528-01 Moderate: ucd-snmp security update

Files available:
ucd-snmp-4.2.5-8.AS21.7.i386.rpm
ucd-snmp-devel-4.2.5-8.AS21.7.i386.rpm
ucd-snmp-utils-4.2.5-8.AS21.7.i386.rpm

More details are available from the RedHat web site at
https://rhn.redhat.com/errata/rh21as-errata.html

The easy way to make sure you are up to date with all the latest patches is to run:
# yum update