Multiple Mediaburst/Clockwork Plugins - Cross-Site Scripting (XSS)

Reflected XSS via GET parameter "to".

Vulnerable Plugins:

1. Clockwork Free and Paid SMS Notifications
Version 2.0.3 | By Clockwork

2. Two-Factor Authentication - Clockwork SMS
Version 1.0.2 | By Clockwork 

3. Booking Calendar - Clockwork SMS 
Version 1.0.5 |By Mediaburst
4. Contact Form 7 - Clockwork SMS
Version 2.3.0 |By Mediaburst
5. Fast Secure Contact Form - Clockwork SMS
Version 2.1.2|By Mediaburst
6. Formidable - Clockwork SMS
Version 1.0.2|By Mediaburst
7. Gravity Forms - Clockwork SMS
Version 2.2 |By Mediaburst

8. WP e-Commerce - Clockwork SMS
Version 2.0.5 | By Mediaburst 

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:


A logged in Administrator, who will click on the above link, he will 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.


1. Login to your wordpress as an admin.
2. Access the following link:


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 or dynamicaly by altering the payload.


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)

Note: 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.


2 Nov 2017: Initial Contact with the vendor.
2 Nov 2017: Response from the vendor which provided different contact details.
2 Nov 2017: Contact with the vendor.
7 Nov 2017: Contact with wordpress (
8 Nov 2017: Wordpress acknowledges the issue and closes the plugins (preventing new downloads).
21 Nov 2017: Vendor acknowledges.
12 Dec 2017: Vendor releases updated version.
Proof of Concept

Affects Plugins

fixed in version 3.0.0
fixed in version 1.1.0
fixed in version 2.4.0
fixed in version 1.1.0
fixed in version 2.4.0
fixed in version 2.4.2


CVE 2017-17780
CVE 2017-18489
CVE 2017-18495
CVE 2017-18555


Type XSS
OWASP Top 10 A7: Cross-Site Scripting (XSS)


Submitter Dimopoulos Elias
Submitter Twitter DimopoulosElias
Views 8934
Verified No


Publicly Published 2017-12-14 (over 2 years ago)
Added 2017-12-19 (over 2 years ago)
Last Updated 2019-11-28 (6 months ago)

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