The vulnerability stems from insecure serialization/deserialization logic in models.py. The original from_value function skipped pickling for strings, allowing attackers to store malicious pickled payloads as raw bytes. The to_value function then deserialized these payloads via pickle.loads() without validation. The patch removed the string bypass in from_value (forcing all values to be pickled) and eliminated unsafe fallback logic in to_value, confirming these functions as the root cause.