Fine-tuning the firewall

When publishing a PBX on a public IP address, the task arises to protect the speaker from scanners, pests who are trying to pick up passwords to SIP PBX accounts. If a simple numeric password is set, it will be picked up very quickly, which will cause losses.

For basic protection against scanners, fail2ban must be enabled. Additionally, you can fine-tune the iptables rules.

1. Go to the "System file customization" section

"System file customization" section

1. Go to edit the /etc/firewall_additional file

File "/etc/firewall_additional"

1. Set the "Add to end of file" mode, insert the following code:

iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'friendly-scanner' --algo bm --to 65535 -j DROP

The code for the file "/etc/firewall_additional"

The added rule allows blocking all incoming requests over the UDP protocol that contain the substring "friendly-scanner"

A more complete example of a set of rules:

iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'sipcli' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'sip-scan' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'iWar' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'sipvicious' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'sipsak' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'sundayddr' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'VaxSIPUserAgent' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p udp -m udp --dport 5060 -m string --string 'friendly-scanner' --algo bm --to 65535 -j DROP

iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'sipcli' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'sip-scan' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'iWar' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'sipvicious' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'sipsak' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'sundayddr' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'VaxSIPUserAgent' --algo bm --to 65535 -j DROP
iptables -I INPUT 2 -p tcp -m tcp --dport 5060 -m string --string 'friendly-scanner' --algo bm --to 65535 -j DROP

This will protect you from most scanners that I mention User-Agent when requesting.