🤖 fix: add rehype-sanitize to prevent XSS in markdown rendering #1050
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Previously, the markdown pipeline used rehype-raw to parse HTML but only had rehype-harden which filters URLs in links/images. This left the app vulnerable to XSS via arbitrary HTML elements (like <noun>, <script>, <style>) and event handlers (onclick, onerror, etc.) that could be injected via prompt injection. Add rehype-sanitize to the pipeline with a schema that: - Allows safe HTML elements commonly used in markdown - Allows KaTeX MathML elements for math rendering - Allows details/summary for collapsible sections - Blocks dangerous elements (script, style, form, etc.) - Strips event handlers and other dangerous attributes _Generated with mux_
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Problem
The error
The tag <noun> is unrecognized in this browserindicated that arbitrary HTML tags were being parsed and rendered. This exposed the app to XSS attacks.Root Cause
The markdown rendering pipeline used:
rehype-raw- Parses raw HTML embedded in markdownrehype-harden- Only sanitizes URLs in<a>and<img>tagsThe gap:
rehype-hardendoes NOT strip unknown/dangerous HTML elements (<script>,<style>,<form>,<noun>, etc.) or remove event handlers (onclick,onerror, etc.).Solution
Add
rehype-sanitizeto the plugin chain with a schema that:<details>/<summary>for collapsible sectionsTesting
make static-checkpassesmake typecheckpassesGenerated with
mux