The Relevanssi – A Better Search plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Comment Content in all versions up to, and including, 4.28.3 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. This is only exploitable when the administrator has configured a non-empty value for the "Allowable tags in excerpts" setting, such as the default example value of <p><a><strong>, as the prefix-matching regex must have an allowable tag whose name is a prefix of the injected tag name.