HiddenWall : Linux Kernel Module Generator For Custom Rules With Netfilter

HiddenWall is a Linux kernel module generator for custom rules with netfilter. (block ports, Hidden mode, rootkit functions etc). The motivation: on bad situation, attacker can put your iptables/ufw to fal.

But if you have HiddenWall, the attacker will not find the hidden kernel module that block external access, because have a hook to netfilter on kernel land(think like a second layer for firewall).

My beginning purpose at this project is protect my personal server, now is protect the machines of my friends. When i talk “friends”, i say peoples that don’t know how to write low level code.

Using the HiddenWall you can generate your custom kernel module for your firewall configuration. The low level programmer can write new templates for modules etc…

Also Read – Graffiti : A Tool To Generate Obfuscated One Liners To Aid In Penetration Testing

First step, understand before run

Verify if the kernel version is 3.x, 4.x or 5.x:

uname -r

Clone the repository

git clone https://github.com/CoolerVoid/HiddenWall

Enter the folder

cd HiddenWall/module_generator

Edit your firewall rules in directory rules/server.yaml, the python scripts use that file to generate a new firewall module.

$ cat rules/server.yaml
module_name: SandWall
public_ports: 80,443,53
unhide_key: AbraKadabra
hide_key: Shazam
fake_device_name: usb14
liberate_in_2_out: True
whitelist: machine:
ip: 192.168.100.181
open_ports: 22,21
machine:
ip: 192.168.100.22
open_ports: 22

If you want study the static code to generate, look the content at directory “templates”.

Second step, generate your module

If you want generate a kernel module following your YAML file of rules, follow that command:

$ python3 WallGen.py –template template/hiddenwall.c -r rules/server.yaml

This generate a generic module with rules of server.yaml, if you want to use another template you can use “wall.c”, so template module “hiddenwall” have option to run on hidden mode(is not visible to “# lsmod” for example).

Third step, install your module

To test module:

# cd output; make clean; make
# insmod SandWall.ko

The rule of YAML to generate module is simple, drop all out to in packets, accept ports 80,443 and 53. The machine 192*.181 can connect at ports 22 and 21…

if you use nmap at localhost/127.0.0.1 you can view the ports open… because rule liberate_in_2_out is true.

Password to turn Firewall visible is “AbraKadabra”.

Password to turn Firewall invisible is “Shazam”.

You need to send password for your fake device “usb14”.

To exit module, you need turn visible at “lsmod” command …

# echo “AbraKadabra” > /dev/usb14
# lsmod | grep SandWall
# rmmod SandWall