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A program that has the purpose to block TCP data packets containing a given pattern.
It uses iptables, available in the Linux Kernel >=2.4 .
It can be programmed to block incoming or outgoing traffic just by editing the iptables rule.
It doesn't handle IPv6 packets.
It can also be programmed to send RST/ACK replies to dropped packets in order to kill/continue the connection.

Installing:

1. Make sure to have Python > 3.7
2. Install compile tools: sudo pacman -S base-devel
3. Install git: sudo pacman -S git
4. Make sure to have iptables
5. Install libnetfilter_queue: sudo pacman -S libnetfilter_queue
6. Install NetfilterQueue: git clone https://github.com/kti/python-netfilterqueue
cd python-netfilterqueue
sudo python3 setup.py install
7. Append the iptables rule: sudo iptables -A OUTPUT -j NFQUEUE --queue-num 33 -p tcp --sport 2222, where 2222 is the listening port of a server application to protect
8. Start the script as root: sudo ./main.py -d (-d stands for debug)

Installing:

1. Make sure to have Python > 3.7
2. Install compile tools: sudo apt install build-essential
3. Install git: sudo apt install git
4. Make sure to have iptables
5. Install libnetfilter_queue: sudo apt install libnetfilter-queue-dev
6. Install NetfilterQueue: git clone https://github.com/kti/python-netfilterqueue
cd python-netfilterqueue
sudo python3 setup.py install
7. Append the iptables rule: sudo iptables -A OUTPUT -j NFQUEUE --queue-num 33 -p tcp --sport 2222, where 2222 is the listening port of a server application to protect
8. Start the script as root: sudo ./main.py -d (-d stands for debug)

1. Default: Block outgoing traffic from an application running on the machine (server) to clients: sudo iptables -A OUTPUT -j NFQUEUE --queue-num 33 -p tcp --sport 2222
2. Block incoming traffic from clients to an application running on the machine (server): sudo iptables -A INPUT -j NFQUEUE --queue-num 33 -p tcp --dport 2222

In debug mode the program will print on screen each packet it handles and save it in a .pcap file.
To activate it: sudo ./main.py -d or sudo ./main.py --debug