Roundcube before 1.4.11 allows XSS via crafted Cascading Style Sheets (CSS) token sequences during HTML email rendering.
https://roundcube.net/news/2021/02/08/security-update-1.4.11
https://github.com/roundcube/roundcubemail/commit/9dc276d5f26042db02754fa1bac6fbd683c6d596