Following my talk at SSTIC, I’ve released a new tool called opensvp. Its aim is to cover the attacks described in this talk. It has been published to be able to determine if the firewall policy related to Application Layer Gateways is correctly implemented.
Opensvp implements two type of attacks:
- Abusive usage of protocol commands: an protocol message can be forged to open pinhole into firewall. Opensvp currently implements message sending for IRC and FTP ALGs.
- Spoofing attack: if anti-spooofing is not correctly setup, an attacker can send command which result in arbitrary pinhole being opened to a server.
The document “Secure use of iptables and connection tracking helpers” was published some months ago and it describes how to protect a Netfilter firewall when using connection tracking helpers (the Netfilter name for ALGs).