Not vulnerable. This issue did not affect the versions of squirrelmail as shipped with Red Hat Enterprise Linux 3, 4, or 5.
Updates for squirrelmail released via RHSA-2009:1066 (https://rhn.redhat.com/errata/RHSA-2009-1066.html) fixed original flaw CVE-2009-1579 without introducing CVE-2009-1381.
CVSS v2 metrics
NOTE: The following CVSS v2 metrics and score provided are preliminary and subject to review.
Find out more about Red Hat support for the Common Vulnerability Scoring System (CVSS).