A XSS vulnerability was discovered in python-lxml's clean module. The module's parser didn't properly imitate browsers, which caused different behaviors between the sanitizer and the user's page. A remote attacker could exploit this flaw to run arbitrary HTML/JS code.
https://www.oracle.com//security-alerts/cpujul2021.html
https://www.debian.org/security/2020/dsa-4810
https://security.netapp.com/advisory/ntap-20210521-0003/
https://lists.debian.org/debian-lts-announce/2020/12/msg00028.html