This update for roundcubemail fixes the following issues:

Upgrade to version 1.3.16

This is a security update to the LTS version 1.3. 

It fixes a recently reported stored cross-site scripting (XSS) 
vulnerability via HTML or plain text messages with malicious content.

References:

- CVE-2020-18670: Cross Site Scripting (XSS) vulneraibility via database host and user in /installer/test.php (boo#1187707)
- CVE-2020-18671: Cross Site Scripting (XSS) vulnerability via smtp config in /installer/test.php (boo#1187706)
- CVE-2020-35730: cross-site scripting (XSS) vulnerability via HTML or plain text messages with malicious content (boo#1180399)