The Popup Maker – Boost Sales, Conversions, Optins, Subscribers with the Ultimate WP Popup Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via post_title in all versions up to, and including, 1.24.0 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This requires the attacker to create a post with an HTML entity-encoded payload in the title, which bypasses sanitize_text_field on save and is later decoded and executed by the browser when rendered by the Select2 component.