Stack-based buffer overflow in the _assemble_line function in modules/pam_env/pam_env.c in Linux-PAM (aka pam) before 1.1.5 allows local users to cause a denial of service (crash) and possibly execute arbitrary code via a long string of white spaces at the beginning of the ~/.pam_environment file.
http://secunia.com/advisories/46583
http://secunia.com/advisories/49711
http://security.gentoo.org/glsa/glsa-201206-31.xml