Smart Forms <= 2.6.104 - Unauthenticated Stored Cross-Site Scripting via 'formString' Parameter

Description

The Smart Forms – when you need more than just a contact form plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'formString' parameter in all versions up to, and including, 2.6.104 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The nonce check protecting the rednao_smart_forms_save_form_values AJAX handler is only enforced when the smart_forms_block_anonymous_submissions option is enabled, meaning default installations require no authentication or nonce verification whatsoever to submit and store malicious payloads.