Gravity Forms <= 2.9.30 - Unauthenticated Stored Cross-Site Scripting via Credit Card 'Card Type' Sub-Field

The Gravity Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the Credit Card field's 'Card Type' sub-field (`input_<id>.4`) in all versions up to, and including, 2.9.30. This is due to the `get_value_entry_detail()` method in the `GF_Field_CreditCard` class outputting the card type value without escaping, combined with `get_value_save_entry()` accepting and storing unsanitized user input for the `input_<id>.4` parameter. The Card Type field is not rendered on the frontend form (it is normally derived from the card number), but the backend submission parser blindly accepts it if included in the POST request. This makes it possible for unauthenticated attackers to inject arbitrary web scripts that execute when an administrator views the form entry in the WordPress dashboard.