AMP for WP – Accelerated Mobile Pages <= 1.1.9 - Cross-Site Request Forgery to Comment Submission

The AMP for WP – Accelerated Mobile Pages plugin for WordPress is vulnerable to Cross-Site Request Forgery in versions up to, and including, 1.1.9. This is due to inverted nonce verification logic in the amp_theme_ajaxcomments AJAX handler, which rejects requests with VALID nonces and accepts requests with MISSING or INVALID nonces. This makes it possible for unauthenticated attackers to submit comments on behalf of logged-in users via a forged request granted they can trick a user into performing an action such as clicking on a link, and the plugin's template mode is enabled.