Script firewall-bypass

Script types: hostrule
Categories: vuln, intrusive

Script Summary

Detects a vulnerability in netfilter and other firewalls that use helpers to dynamically open ports for protocols such as ftp and sip.

The script works by spoofing a packet from the target server asking for opening a related connection to a target port which will be fulfilled by the firewall through the adequate protocol helper port. The attacking machine should be on the same network segment as the firewall for this to work. The script supports ftp helper on both IPv4 and IPv6. Real path filter is used to prevent such attacks.

Based on work done by Eric Leblond.

For more information, see:

Script Arguments


The helper to use. Defaults to ftp. Supported helpers: ftp (Both IPv4 and IPv6).


Port to test vulnerability on. Target port should be a non-open port. If not given, the script will try to find a filtered or closed port from the port scan results.


If not using the helper's default port.

Example Usage

nmap --script firewall-bypass <target>
nmap --script firewall-bypass --script-args firewall-bypass.helper="ftp", firewall-bypass.targetport=22 <target>

Script Output

Host script results:
| firewall-bypass:
|_  Firewall vulnerable to bypass through ftp helper. (IPv4)



  • Hani Benhabiles

License: Same as Nmap--See