RTMKit < 2.0.8 - Authenticated (Contributor+) Stored Cross-Site Scripting via Advanced Heading Widget 'Background Text' Parameter

Description

The RTMKit plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the Advanced Heading widget's 'Background Text' parameter in versions up to, and including, 2.0.7 This is due to insufficient output escaping on the 'background_text_heading' setting in the render() function, which concatenates the value directly into an HTML attribute without applying esc_attr(). 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.