SharpKiller – A Deep Dive Into Bypassing AMSI For Enhanced PowerShell Capabilities

Explore the cutting-edge world of PowerShell evasion with ‘SharpKiller.’

In this deep dive, we unravel the inner workings of this tool, designed to bypass AMSI (Antimalware Scan Interface) in real-time, allowing for seamless execution of PowerShell scripts that were once restricted.

Discover how ‘SharpKiller’ empowers security professionals and penetration testers by enhancing their PowerShell capabilities and outsmarting detection mechanisms. Lifetime AMSI bypass AMSI-Killer by @ZeroMemoryEx ported to .NET Framework 4.8.

Newly integrated features:

[ x ] – Live scan for new powershell processes every 0.5 seconds -> Automatically patches new powershell instances

Building The Solution

• Set your platform explicitly to x64 in Build > configuration manager

How Does It Work?

Opcode Scan

• we get the exact address of the jump instruction by searching for the first byte of each instruction this technique is effective even in the face of updates or modifications to the target data set.
• for example : | 48:85D2 | test rdx, rdx | | 74 3F | je amsi.7FFAE957C694 | | 48 : 85C9 | test rcx, rcx | | 74 3A | je amsi.7FFAE957C694 | | 48 : 8379 08 00 | cmp qword ptr ds : [rcx + 8] , 0 | | 74 33 | je amsi.7FFAE957C694 |
• the search pattern will be like this :{ 0x48,'?','?', 0x74,'?',0x48,'?' ,'?' ,0x74,'?' ,0x48,'?' ,'?' ,'?' ,'?',0x74,0x33}

Patch

Before Patch

• The program tests the value of RDX against itself. If the comparison evaluates to 0, the program executes a jump to return. Otherwise, the program proceeds to evaluate the next instruction

• we cant execute “Invoke-Mimikatz”

After Patch

• we patch the first byte and change it from JE to JMP so it return directly

• now we can execute “Invoke-Mimikatz” 

Newly Created Processes

• Sharp-Killer will patch any newly created Powershell processes in near real time.