ip_conntrack_ftp in the IPTables firewall for Linux 2.4 allows remote attackers to bypass access restrictions for an FTP server via a PORT command that lists an arbitrary IP address and port number, which is added to the RELATED table and allowed by the firewall.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6390
http://www.redhat.com/support/errata/RHSA-2001-084.html
http://www.redhat.com/support/errata/RHSA-2001-052.html
http://www.linux-mandrake.com/en/security/2001/MDKSA-2001-071.php3