AMP for WP <= 1.1.17 - Unauthenticated Stored Cross-Site Scripting via 'headline-*' Shortcode Attribute

The AMP for WP – Accelerated Mobile Pages plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'headline-*' Shortcode Attribute in all versions up to, and including, 1.1.17 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. A Subscriber-level user can store a malicious shortcode in their biographical info field; because WordPress core's wp_filter_kses() only strips HTML tags and not shortcode syntax, and because AMP content sanitizers run before do_shortcode() processes the archive description, the synthesized markup is never post-sanitized.