Advanced Custom Fields: Extended < 0.8.9.4 - Authenticated (Contributor+) Stored Cross-Site Scripting via Shortcode

Description

The Advanced Custom Fields: Extended plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'acfe_form' shortcode in versions up to, and including, 0.8.9.3 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.