The HT Mega – Absolute Addons For Elementor plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the ‘marker_title’, 'notification_content', and 'stt_button_text' parameters in all versions up to, and including, 2.8.3 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The vulnerability was partially patched in version 2.8.3.
https://plugins.trac.wordpress.org/changeset/3257530/