The Gravity Forms plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the `form_ids` parameter in the `gform_get_config` AJAX action in all versions up to, and including, 2.9.30

Overview

The Gravity Forms plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the form_ids parameter in the gform_get_config AJAX action in all versions up to, and including, 2.9.30. This is due to the GFCommon::send_json() method outputting JSON-encoded data wrapped in HTML comment delimiters using echo and wp_die(), which serves the response with a Content-Type: text/html header instead of application/json. The wp_json_encode() function does not HTML-encode angle brackets within JSON string values, allowing injected HTML/script tags in form_ids array values to be parsed and executed by the browser. The required config_nonce is generated with wp_create_nonce('gform_config_ajax') and is publicly embedded on every page that renders a Gravity Forms form, making it identical for all unauthenticated visitors within the same 12-hour nonce tick. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link. This vulnerability cannot be exploited against users who are authenticated on the target system, but could be used to alter the target page.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.