TMZ Lair - Underground Coding

Overview

This code was originally published in the first issue of tmp.0ut zine - an ELF Research Group founded by me and a super talented group of friends in early 2021. This project was finished literally minutes before the deadline we set. Living on the edge!

In general, it took me around a couple of months to complete it, most of the time was dedicated to its core infection routine since the auxiliary sections are common file I/O operations that I’m already familiar with. It was somewhat more challenging than Linux.Midrashim as the technique used here is not as trivial to implement and I want to thank everyone that helped me debug the final version. It was great to have those sessions with all of you, I learned a lot.

Overview

My interest in Assembly language started when I was a kid, mainly because of computer viruses of the DOS era. I’ve spent countless hours contemplating my first humble collection of source codes and samples (you can find it at https://github.com/guitmz/virii) and to me, it’s cool how flexible and creative one can get with Assembly, even if its learning curve is steep.

I’m an independant malware researcher and wrote this virus to learn and have fun, expanding my knowledge on the several ELF attack/defense techniques and Assembly in general.

Overview

How can one not find command line art amusing? Specially when we are talking about computer viruses and even more so when referencing MS-DOS ones. The 16 bit era gave us some of the most interesting computer virus payloads of all time, but achieving something like this today is not as “trivial” anymore.

As Linux is my OS of choice, I wanted to find something that could get close to these MS-DOS fun payloads for my own modern viruses, and, while it’s possible to write directly to the framebuffer, I wanted to try something related to terminal emulators instead. Enter ANSI escape sequences.

Overview

Everytime I try to learn a new programming language, I try by port my prependers (Linux.Zariche, Linux.Liora, Linux.Cephei). Despite the code simplicity , it gives me the chance to understand very useful things in a language, like error handling, file i/o, encryption, memory and a few of its core libraries.

This time, Rust is the language and I must say that I was impressed by its compiler and error handling, but the syntax is still not 100% clear to me (as you can see from my rudimentar code in Linux.Fe2O3) and I wish it had a built-in random library too. This code was written in less than 2 days, of course its not pretty, has lots of .unwrap() (already got great input from some people on Reddit to help me with that, will be addressed) so I apologise in advance.

Last month I wrote a [post](https://www.guitmz.com/running-elf-from-memory/) about the `memfd_create` syscall and left some ideas in the end. Today I'm here to show an example of such ideas implemented in an ELF runtime crypter (kinda lame, I know, but good for this demonstration).

What is it?

Glad you asked. Ezuri is a small Go crypter that uses AES to encrypt a given file and merges it with a stub that will decrypt and execute the file from memory (using the previously mentioned memfd_create syscall). My original goal was to write it in Assembly but that would require more time so it is a task for the future.

Something that always fascinated me was running code directly from memory. From [Process Hollowing](https://www.adlice.com/runpe-hide-code-behind-legit-process/) (aka RunPE) to `PTRACE` [injection](https://blog.xpnsec.com/linux-process-injection-aka-injecting-into-sshd-for-fun/). I had some success playing around with it in `C` in the past, without using any of the previous mentioned methods, but unfortunately the code is lost somewhere in the forums of `VXHeavens` (sadly no longer online) but the code was buggy and worked only with Linux 32bit systems (I wish I knew about [shm_open](http://man7.org/linux/man-pages/man3/shm_open.3.html) back then, which is sort of an alternative for the syscall we are using in this post, mainly targeting older systems where `memfd_create` is not available).

Overview and code

Recently, I have been trying to code in assembly a bit, I find it very interesting and I believe every developer should understand at least the basics of it. I chose FASM as my assembler because I think it is very simple, powerful and I like its concepts (like same source, same output). More information about its design can be found here. Anyway, I have written a small tool, memrun, that allows you to run ELF files from memory using the memfd_create syscall, which is available in Linux where kernel version is >= 3.17.

Last year I built a PC with a AMD Ryzen 5 1600 and I was truly impressed. Then now its time for me to get a new laptop and it was only natural to look for something that had AMD in it. I am very excited for my first Thinkpad, I even starting writing the same day as I ordered the unit (which took its damn time to be delived. More than 10 work days when a estimate of 7 was given by Digital River, Lenovo's partner seller in Europe).

I will be using this machine for music production (not professionally, just a hobby), occasional light gaming and work related stuff (I’m a Systems Engineer). Windows will be a secondary OS (for the music stuff mainly, since my DAW of choice - which is Reason - requires it) and Linux (Arch / OpenSUSE) will be my daily driver.

I’ve been running OpenSUSE (Tumbleweed) for some years now and KDE was my Desktop Environment of choice since years ago but before that, I was a die hard user of the Crunchbang (#!) Linux distro, which featured an awesome gray Openbox desktop. The simplicity Crunchbang offered is something that I missed during the years and after I found out that the community had revived the project in the for of Crunchbangplusplus and also Bunsenlabs, I just had to try it again but this time OpenSUSE Tumbleweed was my choice, instead of the good old Debian.

Recently I started using Openbox as my WM again (after a long time with KDE, the nostalgia hit me). After I had everything working as I wanted to, I noticed the lack of a weather indicator in my systray.

Usually, the desktop environments I have used (Gnome, KDE, Mate) have some sort of applet for this included and I really never bothered (when I was using Openbox before, I had some hacky script that would display the weather in my tint2, but I can’t find it anymore). So I came across go-gtk and felt compeled to write my own tiny indicator.

Yup. That’s about it. Fascinating yet simple. I remember when I first read about this years ago and I was amazed (and still am!).