An issue was discovered in Roundcube Webmail before 1.3.12 and 1.4.x before 1.4.5. include/rcmail_output_html.php allows XSS via the username template object.
https://www.debian.org/security/2020/dsa-4700
https://roundcube.net/news/2020/06/02/security-updates-1.4.5-and-1.3.12
https://github.com/roundcube/roundcubemail/releases/tag/1.4.5
https://github.com/roundcube/roundcubemail/releases/tag/1.3.12
https://github.com/roundcube/roundcubemail/commit/37e2bc745723ef6322f0f785aefd0b9313a40f19