xfwp 6.8.2-10.2 (i386 binary) in ubuntu hoary

 The X firewall proxy is an application layer gateway proxy that may be run
 on a network firewall host to forward X traffic across the firewall. Used
 in conjunction with the X server Security extension and authorization
 checking, xfwp constitutes a safe, simple, and reliable mechanism both to
 hide the addresses of X servers located on an intranet and to enforce a
 server connection policy. Xfwp cannot protect against mischief
 originating on an intranet; however, when properly configured it can
 guarantee that only trusted clients originating on authorized external
 Internet hosts will be allowed inbound access to local X servers.