The Advanced iFrame plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'advanced_iframe' shortcode in versions up to, and including, 2023.8 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. CVE-2023-51690 appears to be a potential duplicate of this issue.