The PAM implementation in /bin/login of the util-linux package before 2.11 causes a password entry to be rewritten across multiple PAM calls, which could provide the credentials of one user to a different user, when used in certain PAM modules such as pam_limits.
http://www.securityfocus.com/bid/3415
http://www.securityfocus.com/archive/1/219175
http://www.redhat.com/support/errata/RHSA-2001-132.html
http://www.novell.com/linux/security/advisories/2001_034_shadow_txt.html
http://www.linux-mandrake.com/en/security/2001/MDKSA-2001-084.php3