During a security research I found an authenticated Stored XSS vulnerability.

The name of the plugin is: DSGVO All in one for WP < 4.1

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)

POC

Go the DSGVO AIO > Settings Cookie Notice settings and enabled them, then put the 
following payload in any of the Button Text settings (such as "Button Text (Accept)", 
"Button Text (Personalize)" and "Button Text (Reject)"): 

<img src onerror=alert(/XSS/)> 

The XSS will be trigged in any frontend page 

Additional information

WPSCAN link: https://wpscan.com/vulnerability/e712f83e-b437-4bc6-9511-2b0290ed315d

Plugin has more than 20,000+ active installations.