The Old Posts Highlighter plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 1.0.3. This is due to missing or incorrect nonce validation on the OPH_options function. This makes it possible for unauthenticated attackers to update the plugin's configuration settings without authorization 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/old-posts-highlighter/trunk/OPH_admin.php#L37
https://plugins.trac.wordpress.org/browser/old-posts-highlighter/trunk/OPH_admin.php#L163
https://plugins.trac.wordpress.org/browser/old-posts-highlighter/tags/1.0.3/OPH_admin.php#L37
https://plugins.trac.wordpress.org/browser/old-posts-highlighter/tags/1.0.3/OPH_admin.php#L163