The Admin Custom Login plugin for WordPress is vulnerable to Stored Cross-Site Scripting via admin settings in all versions up to, and including, 3.6.4 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with administrator-level permissions and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This only affects multi-site installations and installations where unfiltered_html has been disabled.
https://plugins.trac.wordpress.org/browser/admin-custom-login/trunk/login-form-screen.php#L162
https://plugins.trac.wordpress.org/browser/admin-custom-login/tags/3.6.3/login-form-screen.php#L162