The map_yp_alias function in functions/imap_general.php in SquirrelMail before 1.4.19-1 on Debian GNU/Linux, and possibly other operating systems and versions, allows remote attackers to execute arbitrary commands via shell metacharacters in a username string that is used by the ypmatch program. NOTE: this issue exists because of an incomplete fix for CVE-2009-1579.
https://www.redhat.com/archives/fedora-package-announce/2009-May/msg01202.html
https://www.redhat.com/archives/fedora-package-announce/2009-May/msg01195.html
http://www.securityfocus.com/archive/1/503718/100/0/threaded
http://www.mandriva.com/security/advisories?name=MDVSA-2009:122