FTP iptables vulnerability in 2.4 kernel

A security hole has been found that does not affect the default
configuration of Red Hat Linux, but can affect some custom
configurations of Red Hat Linux 7.1 only. The bug is specific
to the Linux 2.4 kernel series.

A vulnerability in iptables "RELATED" connection tracking has been
discovered. When using iptables to allow FTP "RELATED" connections
through the firewall, carefully constructed PORT commands can open
arbitrary holes in the firewall.

The iptables system is included in the 2.4 kernel series, but not in
the earlier 2.2 kernel series used in Red Hat Linux 6.x and Red Hat
Linux 7.0.

Red Hat Linux 7.1 uses a 2.4 kernel and provides the ip_conntrack_ftp
module that has this bug. However, Red Hat Linux does not currently
configure iptables (the default firewall configuration uses ipchains
instead), so unless you have explicitly configured iptables and
enabled FTP "RELATED" connections through the firewall, you are not
vulnerable to attack.

Red Hat will be releasing a kernel with this and other bugs fixed
shortly. In the meantime, we strongly recommend that users of
iptables not allow FTP "RELATED" connections.

http://www.tempest.com.br/advisories/01-2001.html
http://www.securityfocus.com/templates/archive.pike?list=1&mid=177070
http://slashdot.org/comments.pl?sid=01/04/19/047249&cid=36

ip_conntrack_ftp