Description

A User can upload .[a-z]html file (e.g. ahtml, bhtml, chtml, ddhtml, AS LONG AS it ends with html) with XSS payload. Upon upload, a URL with malicious html can be accessed and javascript will be executed.

Proof of Concept (taking chtml as example)

Step (1) Login to the demo portal with admin creds at https://demo.microweber.org/demo/admin/

Step (2) Add new > Page > Add file in picture

Step (3) Upload below file with content below and named as xss.chtml <div onmouseover="alert(document.domain)" style="position:fixed;left:0;top:0;width:9999px;height:9999px;"></div>

Step(4) Access the link in response and once you move the cursor, alert box will be prompted

Impact

If an attacker can control a script that is executed in the victim's browser, they might compromise that user, in this case, an admin, by stealing its cookies.