WordPress Plugin Popup Builder 3.69.6 - Multiple Stored Cross Site Scripting

# Exploit Title: WordPress Plugin Popup Builder 3.69.6 - Multiple Stored Cross Site Scripting
# Date: 11/27/2020
# Exploit Author: Ilca Lucian Florin
# Vendor Homepage: https://sygnoos.com
# Software Link: https://wordpress.org/plugins/popup-builder/ / https://popup-builder.com/
# Version: <= 3.69.6
# Tested on: Latest Version of Desktop Web Browsers: Chrome, Firefox, Microsoft Edge

The Popup Builder – Responsive WordPress Pop up – Subscription & Newsletter
Plugin is vulnerable to stored cross site scripting. There are multiple
parameters vulnerable to cross site scripting.

All versions up to 3.69.6 are vulnerable to stored cross site scripting.

More information about this plugin could be found on the following links:

1. https://wordpress.org/plugins/popup-builder/
2. https://popup-builder.com/

Cross site scripting (XSS) is a common attack vector that injects malicious
code into a vulnerable web application. XSS differs from other web attack
vectors (e.g., SQL injections), in that it does not directly target the
application itself. Instead, the users of the web application are the ones
at risk. A successful cross site scripting attack can have devastating
consequences for an online business’s reputation and its relationship with
its clients. Stored XSS, also known as persistent XSS, is the more damaging
of the two. It occurs when a malicious script is injected directly into a
vulnerable web application.

# How to reproduce #

1. Login as Editor or Administrator: https://website.com/wp-login/

2. Go to the following link:
https://website.com/wp-admin/edit.php?post_type=popupbuilder or search for
PopUp Builder and select or create new PopUp.

2. Click edit

3. Search and find: # Custom JS or CSS

4. On JS -> Opening events section, add two payloads, one for #2 section
and one for #3 section, like in the following example:

#2 Add the code you want to run before the popup opens. This will be the
code that will work in the process of opening the popup. true/false
conditions will not work in this phase.

<textarea class="wp-editor-area editor-content" data-attr-event="WillOpen"
placeholder=" #... type your code" mode="text/javascript"
name="sgpb-WillOpen">"><script
src="data:;base64,YWxlcnQoZG9jdW1lbnQuY29va2llKQ=="></script></textarea>

#3 Add the code you want to run after the popup opens. This code will work
when the popup is already open on the page.

<textarea class="wp-editor-area editor-content" data-attr-event="DidOpen"
placeholder=" #... type your code" mode="text/javascript"
name="sgpb-DidOpen">"><script
src="data:;base64,YWxlcnQoZG9jdW1lbnQuY29va2llKQ=="></script></textarea>

5. Click Update

6. Go to https://website.com. The XSS alert will pop up.

# All text-areas from JS section are vulnerable to stored cross site
scripting.

Evidence:

1. https://ibb.co/JvBTq0H
2. https://ibb.co/0KP7NFQ
3. https://ibb.co/3cFnVYF