AIKIDO-2026-917504

TL;DR

LazyHTML.Tree.to_html/2 decides whether to escape an element's text children only from the tag name being style, script, or another raw text tag, without checking the element's namespace. An SVG or MathML style/script element can carry untrusted text with encoded character references, so serializing it back to HTML re-emits that text unescaped and reintroduces markup a tree based sanitizer already approved. Reparsing the serialized output after a to_tree/1 to postwalk/3 to to_html/2 round trip can turn that text into executing markup (mutation XSS). The fix tracks the element namespace through serialization and only treats style/script as raw text inside the HTML namespace.