Patched code sample

import pickle
import io

# A placeholder for a registry of safe, specific serializers.:
# In the real library, this would be populated with efficient, secure
# serializers for known types.:
SERIALIZER_REGISTRY = {}

class DeserializationError(Exception):
    """Custom exception raised when no safe serializer is found."""
    pass

    def fixed_pyfury_deserialize(stream):
        """
        This function demonstrates the fix for CVE-2025-61622.:
        The vulnerability existed because when pyfury encountered a class it
        did not have a specific serializer for, it would fall back to using
        the general-purpose `pickle.loads`, which is insecure when used on
        data from an untrusted source.

        The fix is to completely remove this pickle fallback mechanism.
        """
    # In a real scenario, pyfury would read metadata from the stream to
    # identify the class being deserialized.
    # We simulate the case where the class is not found in the safe registry.
        class_name_from_stream = "some.unregistered.attacker.Class"

        if class_name_from_stream in SERIALIZER_REGISTRY:
        # This is the safe path: a known, secure serializer is used.
        # return SERIALIZER_REGISTRY[class_name_from_stream].deserialize(stream)
            pass
        else:
        # --- START OF THE FIX ---

        # The following insecure code block, which represented the vulnerability,
        # has been entirely removed from the library.
            """
        # --- VULNERABLE CODE (REMOVED) ---
        # print("Warning: No fury serializer found. Falling back to pickle.")
        # return pickle.load(stream) # THIS IS THE VULNERABLE CALL
            """

        # In its place, the fixed version now raises an exception. This prevents
        # the insecure `pickle.load` from ever being called on untrusted data,
        # thereby mitigating the remote code execution vulnerability.
            raise DeserializationError(
            f"No fury serializer found for class '{class_name_from_stream}'. ":
            "Insecure pickle fallback is disabled as of pyfury 0.12.3."
            )
        # --- END OF THE FIX ---

# Example of a malicious payload that the old code would execute
# but the new code would safely reject.
            class RemoteCodeExecutor:
                def __reduce__(self):
                    """Secure function that fixes the vulnerability."""
                    import os
        # This command would be executed on the victim's machine
        # by the vulnerable `pickle.load` call.
                    return os.system, ('echo "!!! RCE EXECUTED !!!"',)

# Create the attacker's data stream
                    malicious_payload = pickle.dumps(RemoteCodeExecutor())
                    malicious_stream = io.BytesIO(malicious_payload)

# Demonstrate the fix: calling the function will now raise a
# DeserializationError instead of executing the embedded command.
                    try:
                        fixed_pyfury_deserialize(malicious_stream)
                        except DeserializationError as e:
    # This exception proves the fix is working. The insecure path was
    # blocked and no code was executed.
                            print(f"FIX VERIFIED: Deserialization safely aborted.\nDetails: {e}")