Unauthenticated attackers can exploit this by sending a crafted request to the wp_ajax_nopriv_jet_form_builder_submit endpoint. The malicious payload is stored verbatim in the WordPress post meta database. When a user interacts with a page containing the 'Select Field' block, the plugin renders the stored raw meta values as option attributes and label content, leading to the execution of the injected script in the context of the user's browser. This vulnerability poses a significant risk for session hijacking and unauthorized administrative actions if an administrator views the compromised page.

Impact

Successful exploitation allows unauthenticated attackers to execute arbitrary JavaScript in the browser of any user viewing a page where the malicious form meta is rendered. This can lead to session token theft, the execution of unauthorized actions within the WordPress dashboard, or credential harvesting, impacting all organizations utilizing versions 3.6.5.4 or earlier of the JetFormBuilder plugin.

Recommendation

1. Patch immediately by updating the JetFormBuilder - Dynamic Blocks Form Builder plugin to a version greater than 3.6.5.4.
2. Audit WordPress site logs for anomalous requests to the wp_ajax_nopriv_jet_form_builder_submit endpoint that include script tags or unusual characters.
3. Deploy web application firewall (WAF) rules to detect and block incoming HTTP requests targeting the jet_form_builder_submit action that contain XSS vectors (e.g., <script>, onerror, onload).