The Link Shield plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 0.5.4. This is due to missing or incorrect nonce validation on the link_shield_menu_options() function. This makes it possible for unauthenticated attackers to update settings and inject malicious web scripts via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.
https://plugins.trac.wordpress.org/browser/link-shield/trunk/link-shield.php#L24