#!/usr/bin/env python3 # kkmoom_pc_writeup.py # ------------------------------------------------------------- # 1️⃣ Extract the .rar → pc.exe # 2️⃣ Dump the first‑stage packed payload (RVA 0x403000) # 3️⃣ Decompress it with the custom LZ‑type routine # 4️⃣ Dump the second‑stage PE (payload.bin) # 5️⃣ Locate the encrypted blob and XOR key in .rdata # 6️⃣ Decrypt → flag # -------------------------------------------------------------
def extract_first_stage(pe_path): import pefile pe = pefile.PE(pe_path) # These RVAs were discovered manually; they are constant for the challenge packed_rva = 0x403000 packed_size = 0x2000 # 8 KiB – enough to cover the blob off = pe.get_offset_from_rva(packed_rva) return pe.__data__[off:off+packed_size] www kkmoom com pc rar
if __name__ == '__main__': packed = open('payload.packed', 'rb').read() unpacked = decompress(packed) open('payload.bin', 'wb').write(unpacked) Running the script produces payload.bin (~13 KB). The file starts with the header again – the packer is nested : the decompressed payload is a second PE executable. 5. Second‑Stage PE – The Real Target file payload.bin # payload.bin: PE32 executable (GUI) Intel 80386, for MS Windows We repeat the same analysis steps on payload.bin . 5.1. Quick string hunt strings -a -n 5 payload.bin | grep -i flag # → No direct flag string, but we see: # "You think this is easy? Think again." 5.2. Import Table inspection r2 -A payload.bin [0x00401000]> iij # The imports are minimal: kernel32.dll (VirtualAlloc, WriteFile, ExitProcess) # No obvious network calls. 5.3. Locate the main routine The entry point ( 0x00401000 ) now points to a standard mainCRTStartup . We follow the call chain: Second‑Stage PE – The Real Target file payload
The buffer buf is filled from an encrypted static array ( encrypted ) using a XOR key that lives in the .rdata section. 5.4. Dump the encrypted blob & the key # Encrypted data location (r2): [0x00401000]> s 0x00406000 # (example address) [0x00406000]> pd 20 # → .rdata: 0x100 bytes = encrypted payload Think again
def run(cmd): return subprocess.check_output(cmd, shell=True).decode()