The Accessibly plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the REST API in all versions up to, and including, 3.0.3. The plugin registers REST API endpoints at /otm-ac/v1/update-widget-options and /otm-ac/v1/update-app-config with the permission_callback set to __return_true, which means no authentication or authorization check is performed. The updateWidgetOptions() function in AdminApi.php accepts user-supplied JSON data and passes it directly to AccessiblyOptions::updateAppConfig(), which saves it to the WordPress options table via update_option() without any sanitization or validation. The stored widgetSrc value is later retrieved by AssetsManager::enqueueFrontendScripts() and passed directly to wp_enqueue_script() as the script URL, causing it to be rendered as a <script> tag on every front-end page. This makes it possible for unauthenticated attackers to inject arbitrary JavaScript that executes for all site visitors by changing the widgetSrc option to point to a malicious external script.