The User Frontend – Membership, User Registration, User Profile, User Directory & Content Restriction with Frontend Post Submission plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the '<taxonomy_field_name> (default: 'category')' parameter in all versions up to, and including, 4.3.13 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. Exploitation requires the target installation to have configured a Taxonomy field in text-input mode with guest post submission enabled on at least one frontend form.