FlawedAmmyy unpacking malware example

 FlawedAmmyy unpacking

https://guidedhacking.com/threads/how-to-unpack-flawedammyy-malware-unpacking-tutorial.16637/

7fb83e646cbabc50bec4b33c8130b5ae

https://app.any.run/tasks/97d8c688-a0ed-4602-af79-2409b6d8cd47/

steps

- open ida

- find bottom of "start" (using graph overview window)

- notice all to "WinMain", take it

- find "ret" near bottom of "WinMain" (using graph overview window)

- look just above & around to find any "call" statements, choose "call" closest to the "ret"

- find return of VirtualAlloc

- follow as it's moved from EAX to a "var_**"

- then moved to a register

- then moved to another "var_**"

- until you find a "call var_**" to near the end of the chain

- switch from graph to text view, find the memory address of the "call" statement (0x0040153F)

- open x32dbg

- right-click in CPU tab, "Go To -> Expression", enter that address "0x0040153F"

- cursor should be at same "call" statement as we had in IDA

- set a breakoint in x32dbg on that "call" statement (F2)

- push the play arrow (twice) and run to the breakpoint

- right-click on the "call" statement, choose "Follow in Dump -> Value" (no MX value yet)

- step into the "call" (F7)

- notice code has lots of Stack Strings (API calls like VirtualAlloc, VirtualProtect, etc.)

- when you see "VirtualAlloc", good time to put a breakpoint on all future calls (command: bp VirtualAlloc)

- scroll down until you find either a "call REGISTER", "jmp REGISTER", or "call/jmp DWORD that was a register"

ex: mov dword ptr ss:[ebp-54],eax

call word ptr ss:[ebp-54]

- set a breakpoint (F2) on the registry call

- then run by hitting play arrow

- If "VirtualAlloc" breakpoint is hit, right-click on EAX and "Follow in Dump"

- Keep going until the "Follow in Dump" shows a value at the bottom starting with "MZ" header

- open Hex Editor

- compare original EXE first chars after "MZ" header with what is in "Follow in Dump"

- if same, then hit play arrow again to keep running

- if different, then you may have the unpacked EXE

notes: It may take a while (unpacking can be slow)

When you hit a breakpoint you're looking at the content of "previous" memory regions

- right click "Follow in Memory Map"

- right click "Dump Memory to File"

- how do you know if you did it right?

drop into PE Studio, look at strings, do you see the actual "Ammyy.Service" or "ammy\svn" strings?