Hugo versions 0.75.0 through 0.165.x contain a stored cross-site scripting vulnerability: the syntax highlighter does not escape the lineAnchors option before passing it to Chroma, which writes the value verbatim into the id and href attributes of the generated line-number markup. A crafted lineAnchors value supplied as a Markdown code fence attribute (or passed to the highlight template function) results in unescaped HTML in the rendered page, allowing arbitrary JavaScript to execute in the browsers of visitors to the generated site. This affects sites that build and publish Markdown from untrusted contributors; Hugo's security model otherwise considers content trusted input. Fixed in 0.166.0, where the lineAnchors value is HTML-escaped before being passed to Chroma.