Insert Pages <= 3.11.4 - Authenticated (Author+) Stored Cross-Site Scripting via Custom Field Keys (Meta Key Names)

Summary

The Insert Pages plugin for WordPress is vulnerable to Stored Cross-Site Scripting via post custom field keys (meta key names) in all versions up to, and including, 3.11.4. This is due to insufficient output escaping in the the_meta() function: while the custom field VALUE is sanitized with wp_kses_post(), the custom field KEY ($key) is interpolated into the rendered HTML (lines 1786-1791) and echoed (line 1806) without any escaping when an inserted page is rendered with the [insert page='ID' display='all'] shortcode. This makes it possible for authenticated attackers, with author-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.