From Squirrelmail vulnerability report:
An issue was fixed that allowed phishing and cross-site scripting (XSS) attacks to be run by surreptitious placement of content in specially-crafted emails sent to SquirrelMail users.
Credits: Luc Beurton
squirrelmail-1.4.18-1.fc9 has been submitted as an update for Fedora 9.
squirrelmail-1.4.18-1.fc9 has been pushed to the Fedora 9 stable repository. If problems still persist, please make note of it in this bug report.
squirrelmail-1.4.18-1.fc11 has been pushed to the Fedora 11 stable repository. If problems still persist, please make note of it in this bug report.
squirrelmail-1.4.18-1.fc10 has been pushed to the Fedora 10 stable repository. If problems still persist, please make note of it in this bug report.
functions/mime.php in SquirrelMail before 1.4.18 does not protect the
application's content from Cascading Style Sheets (CSS) positioning in
HTML e-mail messages, which allows remote attackers to spoof the user
interface, and conduct cross-site scripting (XSS) and phishing
attacks, via a crafted message.
This issue has been addressed in following products:
Red Hat Enterprise Linux 3
Red Hat Enterprise Linux 4
Red Hat Enterprise Linux 5
Via RHSA-2009:1066 https://rhn.redhat.com/errata/RHSA-2009-1066.html