pam_unix.so in Linux-PAM 0.99.7.0 allows context-dependent attackers to log into accounts whose password hash, as stored in /etc/passwd or /etc/shadow, has only two characters.
osvdb.org/32017
secunia.com/advisories/23858
www.novell.com/linux/security/advisories/2007_3_sr.html
www.redhat.com/archives/fedora-devel-list/2007-January/msg01271.html
www.redhat.com/archives/fedora-devel-list/2007-January/msg01277.html
www.securityfocus.com/bid/22204
www.vupen.com/english/advisories/2007/0323
exchange.xforce.ibmcloud.com/vulnerabilities/31739
www.redhat.com/archives/pam-list/2007-January/msg00017.html