tirdad (pronounce /tērdäd/) is a kernel module to hot-patch the Linux kernel to generate random Initial Sequence Numbers for TCP connections.

You can refer to this blog post to get familiar with the original issue:

https://bitguard.wordpress.com/?p=982

For the build process you will need to have the correct kernel header files already installed on your system. These header files are usually available in your apt repositories.

An example installation of the header files:

apt-get install linux-headers-`uname -r`

Compile by running:

$make

Run as root:

#insmod module/tirdad.ko

You can also disable the module with:

#echo 0 | tee /sys/kernel/livepatch/tirdad/enabled

#rmmod module/tirdad.ko

If you use the legacy version, you only need to run rmmod (the second command).

After you disable it, kernel will continue to use its default algorithm to generate initial sequence numbers.

For kernels 6.18.17 and newer, tirdad randomizes both ISN and initial TCP timestamp offset (if enabled).