Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in dashbitco lazy_html allows mutation XSS via a parse and serialize round-trip of attacker-supplied HTML.
LazyHTML.to_html/2 and LazyHTML.Tree.to_html/2 decide whether to escape an element's text from its tag name alone. A style or script element inside SVG or MathML foreign content is parsed with character references decoded, but is serialized as an HTML raw-text element, so its text is emitted unescaped. Encoded markup such as </style><img src=x onerror=...> inside <svg><style> therefore closes the element on re-parse and becomes live markup. Applications that parse untrusted HTML with lazy_html, filter the document or tree, and serialize it for display are affected, since the payload is a plain text node that no element or attribute filter sees.
This issue affects lazy_html: from 0.1.0 before 0.1.13.