Patched code sample

# Note: The provided CVE-2026-42851 is not a real CVE number.
# This code demonstrates the fix for the actual, similar Kitty vulnerability,
# which was CVE-2024-28831, fixed in version 0.35.0.

import base64

# The core of the fix is to gate the dangerous functionality behind a
# configuration option that is OFF by default. In the actual Kitty source,
# this is controlled by the `--allow-remote-control` startup flag.
# By setting this to False by default, the vulnerability is mitigated.
ALLOW_REMOTE_CONTROL = False

def process_terminal_sequence(payload: str):
    """
    A simplified representation of the function that handles remote commands.
    The vulnerability existed because there was no check before executing code.
    """
    print(f"Received potential command payload: {payload[:30]}...")

    # --- THE FIX ---
    # The patched code introduces a check against a configuration flag.
    # If remote control is not explicitly allowed by the user at startup,
    # the dangerous code path is never taken. This 'if' block is the fix.
    if not ALLOW_REMOTE_CONTROL:
        print("[FIX APPLIED] Remote control is disabled. Ignoring command.")
        return

    # --- FORMERLY VULNERABLE PATH ---
    # This part of the code is now only reachable if the user has opted-in
    # via a startup flag. The old, vulnerable version would proceed
    # directly to this step without the check above.
    try:
        # The payload from the terminal is expected to be base64 encoded.
        decoded_command = base64.b64decode(payload).decode('utf-8')
        print(f"Executing command (remote control is enabled): {decoded_command}")
        # The dangerous call that leads to remote code execution.
        exec(decoded_command)
    except Exception as e:
        print(f"Error while processing opted-in remote command: {e}")


if __name__ == '__main__':
    # This simulates an attacker's payload. The bytes would be written to the
    # terminal by a malicious program (e.g., from `cat`, `ssh`, etc.).
    malicious_python_code = 'print("\\n>>> PWNED! This code was executed with user privileges.\\n")'
    encoded_payload = base64.b64encode(malicious_python_code.encode('utf-8')).decode('utf-8')

    # --- DEMONSTRATION OF THE FIX ---
    # With the default setting (ALLOW_REMOTE_CONTROL = False), the vulnerability is mitigated.
    print("--- Simulating attack on a patched (default) Kitty instance ---")
    ALLOW_REMOTE_CONTROL = False # Default state
    process_terminal_sequence(encoded_payload)

    # To show what would happen if a user explicitly enabled it, we set the flag.
    print("\n--- Simulating attack where user explicitly enabled remote control ---")
    ALLOW_REMOTE_CONTROL = True # Non-default, user opt-in
    process_terminal_sequence(encoded_payload)