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deobfuscate_resolve_Vidar.py
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deobfuscate_resolve_Vidar.py
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import string
import idaapi
import idc
import idautils
import base64
import json
import string
MOD = 256
def KSA(key):
key_length = len(key)
S = range(MOD)
j = 0
for i in range(MOD):
j = (j + S[i] + key[i % key_length]) % MOD
S[i], S[j] = S[j], S[i]
return S
def PRGA(S):
i = 0
j = 0
while True:
i = (i + 1) % MOD
j = (j + S[i]) % MOD
S[i], S[j] = S[j], S[i]
K = S[(S[i] + S[j]) % MOD]
yield K
def get_keystream(key):
S = KSA(key)
return PRGA(S)
global strings_dict, procs_dict
strings_dict = {}
def decrypt_strings(main_refsList):
"""decryption sequence
push offset aLq ; "LQ=="
call sub_422F70
add esp, 4
mov dword_4321D, eax
"""
wrapper_decryptStrings = idc.LocByName(main_refsList[0])
idc.MakeName(wrapper_decryptStrings, "wrapper_decryptStrings_"+main_refsList[0])
decryptList = list(FuncItems(wrapper_decryptStrings))
refsFrom_decryptList = [idc.GetOpnd(line,0) for line in decryptList if idc.GetMnem(line) == 'call']
print len(refsFrom_decryptList)
result = False
sub_decryptaddr = ''
if refsFrom_decryptList:
result = all(element == refsFrom_decryptList[0] for element in refsFrom_decryptList)
if result:
sub_decryptaddr = set(refsFrom_decryptList)
sub_decrypt = idc.LocByName(list(sub_decryptaddr)[0])
idc.MakeName(sub_decrypt, "b64_RC4_decrypt")
key = ''
for addr in decryptList:
optype = idc.GetOpType(addr,0)
if optype == 2:
# print idc.GetDisasm(addr)
idc.MakeName(idc.GetOperandValue(addr,0), "key_offset")
key = idc.GetString(idc.GetOperandValue(addr,1))
break
key = [ord(c) for c in key.encode('UTF-8')]
sequence = ['push', 'call', 'add', 'mov']
plaintext = ''
for i in range(0, len(decryptList)-len(sequence)):
if idc.GetMnem(decryptList[i]) in sequence:
if idc.GetMnem(idc.NextHead(decryptList[i])) == 'call' and idc.GetOperandValue(idc.NextHead(decryptList[i]),0) == sub_decrypt:
data = idc.GetString(idc.GetOperandValue(decryptList[i],0))
decoded_data = bytearray(base64.b64decode(data))
keystream = get_keystream(key)
res = []
for byte in decoded_data:
val = byte ^ next(keystream)
if val != 0:
res.append(chr(val))
else:
res.append('?')
plaintext = ''.join(res)
# print plaintext
idc.MakeComm(decryptList[i], plaintext)
var_addr = idc.GetOperandValue(decryptList[i + 3],0)
strings_dict[var_addr] = plaintext
plaintext = "".join([c for c in plaintext if (c in string.ascii_letters or c in string.digits)]).capitalize()
plaintext = "str_" + plaintext
idc.MakeName(var_addr, plaintext)
def resolve_apis(main_refsList):
"""GetProcaddress call pattern
mov ecx, str_Exitprocess
push ecx ; lpProcName
mov edx, [ebp+pKernel32Base]
push edx ; hModule
call getprocaddress
mov dword_4317B4, eax
"""
pattern = ['mov', 'push', 'mov', 'push', 'call', 'mov']
resolveList = list(FuncItems(idc.LocByName(main_refsList[1])))
resolve_addrList = list(FuncItems(idc.LocByName(main_refsList[1])))
idc.MakeName(idc.LocByName(main_refsList[1]), "resolveAPIs_"+main_refsList[1])
resolve_refsList = [idc.GetOpnd(line,0) for line in resolve_addrList if idc.GetMnem(line) == 'call']
idc.MakeName(idc.LocByName(resolve_refsList[0]), "load_kernel32dll_"+resolve_refsList[0])
idc.MakeName(idc.LocByName(resolve_refsList[1]), "parse_kernel32dll_"+resolve_refsList[1])
ea = idc.LocByName("parse_kernel32dll_"+resolve_refsList[1])
xref = idautils.XrefsTo(ea, 0)
loadlib_ref = idc.NextHead(idc.NextHead(next(xref).frm))
idc.MakeName(idc.GetOperandValue(loadlib_ref, 0), "loadlibraryA")
getprocaddr_ref = idc.NextHead(idc.NextHead(next(xref).frm))
idc.MakeName(idc.GetOperandValue(getprocaddr_ref, 0), "getprocaddress")
for i in range(0, len(resolveList)-len(pattern)):
if idc.GetMnem(resolveList[i]) == 'call' and "getprocaddress" in idc.GetOpnd(resolveList[i], 0):
addr = idc.GetOperandValue(resolveList[i-4],1)
if addr in strings_dict:
api = strings_dict[addr]
resolvedaddr = idc.GetOperandValue(resolveList[i+1],0)
idc.MakeName(resolvedaddr, "_"+api)
if __name__ == "__main__":
main_addrList = list(FuncItems(idc.LocByName("_WinMain@16")))
main_refsList = [idc.GetOpnd(line,0) for line in main_addrList if idc.GetMnem(line) == 'call']
decrypt_strings(main_refsList)
resolve_apis(main_refsList)
idc.MakeName(idc.LocByName(main_refsList[2]), "CIS_check_"+main_refsList[2])
idc.MakeName(idc.LocByName(main_refsList[3]), "windowsdefender_check_"+main_refsList[3])
idc.MakeName(idc.LocByName(main_refsList[4]), "grabbing_module_"+main_refsList[4])