183 lines
7.3 KiB
Python
183 lines
7.3 KiB
Python
from .Challenge import Challenge
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import subprocess
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import time
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import re
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import os
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class Sheesh(Challenge):
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flag_location = 'flags/sheesh.txt'
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history_location = 'history/sheesh.txt'
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_CONTAINER = "sheesh_container"
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_SERVICE_CMD = ["docker", "exec", "-i", _CONTAINER, "python3", "/home/ctfuser/chall/src/chall.py"]
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_HEX_RE = re.compile(r'^[0-9a-fA-F]+$')
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def _read_container_flag(self) -> str:
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out = subprocess.run(["docker", "exec", self._CONTAINER, "cat", "/flag.txt"],
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capture_output=True, text=True)
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if out.returncode != 0 or not out.stdout.strip():
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raise FileNotFoundError("Flag not found in container (/flag.txt)")
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return out.stdout.strip()
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def _spawn(self):
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return subprocess.Popen(
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self._SERVICE_CMD,
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stdin=subprocess.PIPE,
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stdout=subprocess.PIPE,
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stderr=subprocess.STDOUT,
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text=True,
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bufsize=0,
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)
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def _read_until(self, proc, token, timeout=5.0, max_bytes=1_000_000):
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start = time.time()
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buf = []
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r = proc.stdout.read
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while True:
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if time.time() - start > timeout:
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tail = ''.join(buf)[-500:]
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raise TimeoutError(f"Timeout waiting for '{token}'. Got so far:\n{tail}")
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ch = r(1)
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if ch == "" and proc.poll() is not None:
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raise RuntimeError(f"Process ended while waiting for '{token}'. Output:\n{''.join(buf)}")
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buf.append(ch)
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if len(buf) > max_bytes:
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raise RuntimeError("Exceeded max read size")
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if token in "".join(buf):
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return "".join(buf)
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def _send_line(self, proc, s: str):
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proc.stdin.write(s + "\n")
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proc.stdin.flush()
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def _expect_hex_field(self, text: str, label: str) -> str:
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m = re.search(rf"{re.escape(label)}\s*:\s*([0-9a-fA-F]+)", text)
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assert m, f"Missing '{label}' in output. Tail:\n{text[-400:]}"
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hx = m.group(1)
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assert self._HEX_RE.match(hx), f"{label} is not hex"
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return hx
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def distribute(self, flag):
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try:
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os.makedirs(os.path.dirname(self.flag_location), exist_ok=True)
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with open(self.flag_location, 'w') as f:
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f.write(flag)
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os.makedirs(os.path.dirname(self.history_location), exist_ok=True)
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with open(self.history_location, 'a') as f:
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f.write(flag + '\n')
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self.logger.info(f'Flag {flag} written to {self.flag_location}')
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return True
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except Exception as e:
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self.logger.error(f'Could not write flag to {self.flag_location}: {e}')
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return False
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def check(self):
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try:
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with open(self.flag_location, 'r') as f:
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host_flag = f.read().strip()
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container_flag = self._read_container_flag()
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assert host_flag == container_flag, 'Flag mismatch between host and container'
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self.logger.info('[ok] flag parity (sheesh)')
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proc = self._spawn()
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def menu():
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self._read_until(proc, "> ", timeout=5.0)
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menu()
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self._send_line(proc, "1")
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self._read_until(proc, "pt: ", timeout=3.0)
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pt_hex = "414243444546"
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self._send_line(proc, pt_hex)
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out = self._read_until(proc, "\n\n", timeout=3.0)
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ct_hex = self._expect_hex_field(out, "ct")
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ct = bytes.fromhex(ct_hex)
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assert len(ct) == 16 + len(bytes.fromhex(pt_hex)), "CFB ct length mismatch (IV+PT)"
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iv_a = ct[:16]
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self.logger.info("[ok] encrypt(1) basic")
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menu()
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self._send_line(proc, "1")
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self._read_until(proc, "pt: ", timeout=3.0)
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pt_hex2 = "00" * 8
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self._send_line(proc, pt_hex2)
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out2 = self._read_until(proc, "\n\n", timeout=3.0)
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ct2_hex = self._expect_hex_field(out2, "ct")
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ct2 = bytes.fromhex(ct2_hex)
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assert len(ct2) == 16 + len(bytes.fromhex(pt_hex2)), "Second CFB ct length mismatch"
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iv_b = ct2[:16]
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assert iv_a != iv_b, "CFB IV appears reused"
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self.logger.info("[ok] encrypt(1) IV rotates")
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menu()
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self._send_line(proc, "3")
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self._read_until(proc, "pt: ", timeout=3.0)
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self._send_line(proc, "00" * 15)
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out3a = self._read_until(proc, "\n", timeout=3.0)
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assert "hmmm" in out3a.lower(), "Option 3 must reject non-16-byte input (15B)"
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menu()
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self._send_line(proc, "3")
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self._read_until(proc, "pt: ", timeout=3.0)
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self._send_line(proc, "00" * 17)
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out3b = self._read_until(proc, "\n", timeout=3.0)
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assert "hmmm" in out3b.lower(), "Option 3 must reject non-16-byte input (17B)"
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menu()
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self._send_line(proc, "3")
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self._read_until(proc, "pt: ", timeout=3.0)
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self._send_line(proc, "11" * 16)
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out3 = self._read_until(proc, "\n\n", timeout=3.0)
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ct3_hex = self._expect_hex_field(out3, "ct")
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ct3 = bytes.fromhex(ct3_hex)
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assert len(ct3) in (16, 32), f"Unexpected CT length for option 3: {len(ct3)} (expected 16 or 32)"
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if len(ct3) == 16:
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self.logger.info("[ok] get third(3): vuln flavor (16-byte CT)")
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else:
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self.logger.info("[ok] get third(3): patched flavor (32-byte CT)")
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menu()
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self._send_line(proc, "3")
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out4 = self._read_until(proc, "\n", timeout=3.0)
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assert "sheesh" in out4.lower(), "Second call to option 3 should be rejected with 'sheesh'"
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self.logger.info("[ok] get third(3) lockout")
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menu()
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self._send_line(proc, "2")
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out5 = self._read_until(proc, "\n\n", timeout=3.0)
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iv1_hex = self._expect_hex_field(out5, "iv1")
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iv2_hex = self._expect_hex_field(out5, "iv2")
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ct5_hex = self._expect_hex_field(out5, "ct")
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assert len(bytes.fromhex(iv1_hex)) == 16, "iv1 length invalid"
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assert len(bytes.fromhex(iv2_hex)) == 16, "iv2 length invalid"
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assert len(bytes.fromhex(ct5_hex)) >= 16 and len(bytes.fromhex(ct5_hex)) % 16 == 0, "CBC ct invalid length"
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self.logger.info("[ok] profit(2) first call")
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menu()
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self._send_line(proc, "2")
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out6 = self._read_until(proc, "\n\n", timeout=3.0)
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iv1_hex_2 = self._expect_hex_field(out6, "iv1")
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iv2_hex_2 = self._expect_hex_field(out6, "iv2")
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assert iv1_hex_2 != iv1_hex or iv2_hex_2 != iv2_hex, "IVs did not change between consecutive '2' calls"
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self.logger.info("[ok] profit(2) fresh IVs")
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menu()
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self._send_line(proc, "4")
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try:
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proc.wait(timeout=2.0)
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except subprocess.TimeoutExpired:
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proc.kill()
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raise AssertionError("Program did not exit after option 4")
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self.logger.info("[ok] service exit on 4")
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self.logger.info('Check passed for sheesh')
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return True
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except Exception as e:
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self.logger.error(f'Could not check sheesh: {e}')
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return False
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