Cure53 DOMPurify before 2.0.17 allows mutation XSS. This occurs because a serialize-parse roundtrip does not necessarily return the original DOM tree, and a namespace can change from HTML to MathML, as demonstrated by nesting of FORM elements.
github.com/cure53/DOMPurify/commit/02724b8eb048dd219d6725b05c3000936f11d62d
github.com/cure53/DOMPurify/compare/2.0.16...2.0.17
lists.debian.org/debian-lts-announce/2020/10/msg00029.html
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-26870
research.securitum.com/mutation-xss-via-mathml-mutation-dompurify-2-0-17-bypass/
www.oracle.com//security-alerts/cpujul2021.html