University of Washington IMAP Toolkit 2007f on UNIX, as used in imapopen() in PHP and other products, launches an rsh command (by means of the imaprimap function in c-client/imap4r1.c and the tcpaopen function in osdep/unix/tcpunix.c) without preventing argument injection, which might allow remote attackers to execute arbitrary OS commands if the IMAP server name is untrusted input (e.g., entered by a user of a web application) and if rsh has been replaced by a program with different argument semantics. For example, if rsh is a link to ssh (as seen on Debian and Ubuntu systems), then the attack can use an IMAP server name containing a "-oProxyCommand" argument.