CVE 2009-2904
A certain Red Hat modification to the ChrootDirectory feature in OpenSSH 4.8, as used in sshd in OpenSSH 4.3 in Red Hat Enterprise Linux (RHEL) 5.4 and Fedora 11, allows local users to gain privileges via hard links to setuid programs that use configuration files within the chroot directory, related to requirements for directory ownership.
See the 
CVE page on Mitre.org
for more details.
