Previous blog posts addressed the issue of static artefacts that can easily be caught by security software, such as strings and API imports:
This one provides an additional layer of obfuscation to target another kind of detection mechanism used to monitor a program’s activity, i.e userland hooks.
Continue reading Engineering antivirus evasion (Part III)
In our journey to try and make our payload fly under the radar of antivirus software, we wondered if there was a simple way to encrypt all the strings in a binary, without breaking anything. We did not find any satisfying solution in the literature, and the project looked like a fun coding exercise so we decided it was worth a shot.
Continue reading Statically encrypt strings in a binary with Keystone, LIEF and radare2/rizin
This blog post accompanies the talk we gave at Insomni’hack 2022. The source code as well as the slides can be found at:
Continue reading Automatically extracting static antivirus signatures
tl;dr To interact with the Windows operating system, software often import functions from Dynamic Link Libraries (DLL). These functions are listed in clear-text in a table called Import Address Table and antivirus software tend to capitalise on that to infer malicious behavioural detection. We show ideas and implementation of an obfuscator that allows to refactor any C/C++ software to remove this footprint, with a focus on Meterpreter. The source code is available at https://github.com/scrt/avcleaner.
Continue reading Engineering antivirus evasion (Part II)
tl;dr: this blog post documents some aspects of our research on antivirus software and how we managed to automatically refactor Meterpreter to bypass every AV/EDR we were put up against. While the ideas for every technique and the implementation of the string obfuscation pass are detailed below, we decided to publish details on API imports hiding / syscalls rewriting in future blog posts to keep this one as short as possible. The source code is available at https://github.com/scrt/avcleaner
Continue reading Engineering antivirus evasion
Lors d’un pentest, il n’est pas rare de rencontrer un serveur proxy filtrant l’accès Internet. Dans certains cas, le proxy va jusqu’à analyser les fichiers téléchargés afin de vérifier qu’ils ne contiennent pas de virus, ce qui peut être problématique.
Continue reading Bypass “Simple” de proxy antivirus