How to use nim-lang kill-free test
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Nim-lang kill-free test: callback function combined with steganography
Is to hide shellcode, such as beacon.bin, in a PNG image, of course, after being encrypted by AES before embedding the image. At run time, the shellcode is extracted and finally injected into shellcode through callback.
Steganography
I wanted to use https://github.com/treeform/steganography directly, but I ruthlessly reported an error:
Reading the code found that, in fact, the information is hidden in the PNG picture each pixel RGBA in the lowest two bits, so a pixel can hide 8 bits, that is, 1 byte of data. Another pit is how to identify how much data is embedded and finally decide to save the size of the embedded data with the first 8 bytes. The code for this part is kept in lsb.nim.
The encryption and decryption part uses AES256-CTR and refers to the encrypt_decrypt_bin.nim of OffensiveNim.
Generate encrypted pictures
Compile lsb.nim
Nim c-d:realese-- opt:size-- cpu:amd64 lsb.nim
Generate encrypted pictures
Restore a file
Compared with the restored file, it is found that the hash is consistent with the original file, which shows that it is correct.
Inject shellcode
Note: the local test has updated windows 10 defender to the latest (if the first time is unsuccessful, you can try a second time).
Currently, there are 17 built-in methods to inject shellcode through callback, and the runtime chooses one as soon as possible. The implementation of this part can be found in my previous article, Shellcode Injection via Callbacks.
Compile letsgo.nim
Nim c-d:realese-d:ssl-opt:size-cpu:amd64 letsgo.nim
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