From SquirrelMail vulnerability report:
An issue was fixed that allowed arbitrary server-side code execution when SquirrelMail was configured to use the example "map_yp_alias" username mapping functionality.
Credits: Niels Teusink
Updated upstream patch (2009-05-21):
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.
The map_yp_alias function in functions/imap_general.php in
SquirrelMail before 1.4.18 allows remote attackers to execute
arbitrary commands via shell metacharacters in a username string that
is used by the ypmatch program.
CVE-2009-1381 (incomplete upstream fix for CVE-2009-1579) now public:
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