The cupsDoAuthentication function in auth.c in the client in CUPS before 1.4.4, when HAVE_GSSAPI is omitted, does not properly handle a demand for authorization, which allows remote CUPS servers to cause a denial of service (infinite loop) via HTTP_UNAUTHORIZED responses.
http://www.vupen.com/english/advisories/2011/0535
http://www.mandriva.com/security/advisories?name=MDVSA-2011:146
http://www.debian.org/security/2011/dsa-2176
http://security.gentoo.org/glsa/glsa-201207-10.xml