Amsi

Resurrecting an old AMSI Bypass

24 June 2020 ~8 min By Philippe Vogler
Amsi Bypass Powershell
While working on DoubleAgent as part of the Introduction To Red Teaming course we’re developing for RingZer0, I had a look at Anti-Malware Scan Interface (AMSI) bypasses. One of the objectives I had was to find a new way to evade AMSI. As with my DoubleAgent work, this did not lead to the identification of a novel finding, but instead revealed that old techniques can be revived with minimal work. This blog post describes how to resurrect the original DLL hijack documented by Cn33liz by extending it to simply define the typically exported functions found in amsi.dll in a fake DLL. This gives a low privileged user an AMSI bypass if they can write to a directory.