Better Comments < 1.5.6 - Subscriber+ Stored XSS

Proof of Concept

1. From the menu on the left, go into "Users" and edit Subscriber user.
2. Upload a new avatar image and click "Update User".
3. Change the nickname to the following payload and click "Update User" as before:
"onload="prompt('XSS')
4. Payload is triggered immediately on Profile menu.
5. Open any post as the Subscriber user and leave a comment to trigger the payload.
6. Everywhere where the avatar is used, the payload is triggered. For example, consider the avatar is always used in the top right corner besides the username on any WordPress page or post.