University of Washington IMAP Toolkit 2007f on UNIX, as used in imap_open()
in PHP and other products, launches an rsh command (by means of the
imap_rimap function in c-client/imap4r1.c and the tcp_aopen function in
osdep/unix/tcp_unix.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if rsh has been replaced by a program with different argument semantics.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.

mdeslaur	php5 in precise and trusty doesn't build imap, it is in a separate php-imap source package.
msalvatore	uw-imap has been defunct since 2008.