Fix Markdown code fence XSS - #829
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yaojin3616
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August 7, 2026 07:46
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Summary
Sanitize Markdown fenced-code language identifiers before they are used to form the rendered
language-*CSS class.Root cause
The Markdown renderer copied the complete fence info string into an HTML attribute that is rendered with
dangerouslySetInnerHTML. A crafted language value could break out of the attribute and execute stored script when the Markdown was viewed.Impact
All surfaces that render persisted Markdown through
MarkdownRendererare protected. Valid common language identifiers, includingts,c++, andc#, continue to render their CSS class; unsafe or malformed identifiers render as an unlabelled code block.Validation
npm test(87 passing)npm run build