WordPress Caldera Forms Cross Site Scripting

Type packetstorm
Reporter Federico Scalco
Modified 2018-04-19T00:00:00


                                            `# Exploit Title: CalderaForms - multiple XSS  
# Date: 02-03-2018  
# Exploit Author: Federico Scalco  
# fscalco at mentat dot is  
# @mindpr00f  
# Vendor Homepage: https://calderaforms.com/  
# Software Link: https://wordpress.org/plugins/caldera-forms/  
# Vulnerable App: https://github.com/CalderaWP/Caldera-Forms/archive/  
# Version: (older versions may also be affected)  
# Tested on: WordPress 4.9.4  
# CVE : i>>?CVE-2018-7747  
"i>>?Caldera Form is a free and powerful WordPress plugin that creates  
responsive forms with a simple drag and drop editor."  
It is reported to have i>>?100,000+ active installations at the moment of this  
The application fails to validate user-supplied input, hence it stores the  
unsanitized buffer in the database.  
The vulnerabilities reported here will be exploitable ONLY if certain  
conditions are met, which is not the case in a CF's default configuration  
(although still being vulnerable).  
A note on buffers containing strings:  
single (') and double (") quotes are correctly escaped, backticks (`)  
are not.  
3.a) Stored XSS - public  
When submitting a CF form, the plugin will show a greeting message to  
notify the user that everything went ok.  
This message is editable by the site's admin and can contain part of the  
user-supplied data (e.g. they're first name). In this case, simply inject  
HTML code into the parameter which gets returned in the greeting message  
and submit the POST request. A JSON response will follow, containing, among  
other data:  
- the greeting message ("html", which contains the malicious payload that  
gets executed right away)  
- form's ID ("form_id")  
- data's ID ("cf_id")  
"html":"<GREETING MESSAGE>",  
At this point, to reach the stored XSS, simply build a GET request using  
the obtained data.  
The malicious payload will be found at  
Vulnerable config:  
- form > form settings > capture entries > checked (ON by default)  
- form > form settings > success message > add some of the user  
supplied fields (absent by default)  
To replicate this on a fresh install:  
- Create a new, default, contact form  
- Go to "Form Settings" tab and edit the success message to include,  
for example, the user's first name.  
e.g.: Form has been successfully submitted. Thank you %first_name%.  
- Save & publish  
- As an unauthenticated user, submit the contact form injecting HTML  
code in first name's parameter. XSS will be triggered right away  
- To recall the payload as a stored XSS, read the POST's response and  
point your browser to  
3.b) Stored XSS - admin interface  
CalderaForms gives the ability to notify the admin via email everytime a  
form gets submitted.  
Furthermore, an admin can choose to enable an "email transacion log" for  
debugging purposes (disabled by default).  
If this configuration is in place, a copy of the malicious payload  
described above will be shown in the administration panel, when visiting  
that form's malicious entry's details.  
Vulnerable config:  
- form > form settings > capture entries > checked (ON by default)  
- form > email > debug mailer > checked (OFF by default)  
To replicate this on a fresh install:  
- Enable the transaction log (form -> edit -> email tab -> check  
"Enable email send transaction log")  
- Replicate the injection described at 3.a (all fields can be used this  
time) as an unauthenticated user  
- Back again in the admin interface, visit form's entries, identify the  
malicious one and click on the "view" button  
This will pop a details window and trigger the XSS.  
3.c) Importing a weaponized form - admin interface  
CalderaForms gives the ability to import a form (JSON format).  
A malicious form field can be crafted which will trigger an XSS when said  
field gets displayed/edited after the import.  
It's worth noting that this flaw does not depend on custom configurations,  
although it's not "remotely" and "automatically" exploitable. The problem  
here arise, for example, when an admin imports a malicious JSON.  
To replicate this on a fresh install:  
- Create a form and export it (JSON format)  
- Edit the json and inject HTML code. "label" and "slug" parameters  
were tested, others may be vulnerable too.  
"label":"First<script>alert(1);</script> Name",  
- Import the malicious form to trigger the XSS in the administration  
Update to the latest version available.  
If any personalized configuration is found exploitable, the following steps  
can be followed, as a temporary mitigation strategy, if no update is  
available or updating is not an option, for whatever reason:  
- for every form, under "Form Settings", prune every variable that gets  
returned to the user as a success message  
- for every form, under the "Email" tab, un-check "Enable email send  
transaction log"  
- for every form that gets imported perform a thorough review  
02-03-18 > vendor gets notified  
06-03-18 > vendor replies  
07-03-18 > CVE requested and assigned  
27-03-18 > patch released  
27-03-18 > vulnerability disclosed  
Special thanks go to Josh Pollock and his team, from Caldera, who invested  
passion and energy in understanding and patching these issues.