The Relevanssi – A Better Search plugin for WordPress is vulnerable to Reflected Cross-Site Scripting in versions up to, and including, 4.28.1 via the 's', 'posttypes', and 'orderby' request parameters. This is due to insufficient input sanitization and output escaping in the relevanssidebugarray() function in lib/debug.php, which dumps user-supplied query variables through printr() inside a <pre> block without HTML escaping. The debug path is enabled by supplying the relevanssidebug=on request parameter when the administrator has previously enabled the 'Debugging mode' setting; the gate itself is a configuration check with no capability, nonce, or logged-in check (the vendor explicitly suppresses nonce verification on that line). 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 specially crafted link.