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.