Echo Knowledge Base WordPress plugin: unauthenticated script injection via config parameter

The Echo Knowledge Base – Documentation, FAQs, Chat & Smart Search plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the 'new_kb_config' parameter (specifically the article-mobile-break-point-v2 key, among other config keys interpolated into the <style> element) in versions up to, and including, 17.214.0 This is due to insufficient input sanitization and output escaping in EPKB_Frontend_Editor::fe_preview_config() and EPKB_Articles_Setup: on every knowledge base article page view, when the request supplies epkb_fe_reload_mode=on, an attacker-controlled JSON blob is merged over the stored KB configuration and several values are concatenated directly into a stylesheet emitted inside a literal <style> element without escaping (minify_css() does not strip <, > or /). This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user (with Editor-level access or above, holding the manage_categories capability, or an Administrator) into performing an action such as clicking on a specially crafted link.