📑 fix: Sanitize Markdown Artifacts#12249
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Replace marked-react with react-markdown + remark-gfm for artifact markdown preview. react-markdown's skipHtml strips raw HTML tags, and a urlTransform guard blocks javascript: and data: protocol links.
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Pull request overview
This PR hardens markdown artifact previews in the client by replacing the current markdown renderer with react-markdown + remark-gfm, aiming to prevent raw HTML rendering and block unsafe link protocols in the sandboxed preview.
Changes:
- Swap
marked-reactforreact-markdownwithremark-gfm, enablingskipHtmland aurlTransformsafety guard. - Update Sandpack markdown artifact dependencies to include
react-markdownandremark-gfm. - Adjust markdown artifact unit tests to reflect the new renderer output.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| client/src/utils/markdown.ts | Updates the generated Sandpack MarkdownRenderer implementation to use react-markdown with HTML skipping and URL protocol filtering. |
| client/src/utils/artifacts.ts | Updates the dependency map for markdown/plaintext artifacts to install react-markdown and remark-gfm in Sandpack. |
| client/src/utils/tests/markdown.test.ts | Updates expectations to match the new generated MarkdownRenderer code. |
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| const markdownDependencies = { | ||
| 'marked-react': '^2.0.0', | ||
| 'react-markdown': '^9.0.1', | ||
| 'remark-gfm': '^4.0.0', |
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| <ReactMarkdown | ||
| remarkPlugins={[remarkGfm]} | ||
| skipHtml={true} | ||
| urlTransform={(url) => (isSafeUrl(url) ? url : '')} | ||
| > | ||
| {content} | ||
| </ReactMarkdown> |
- Convert isSafeUrl from denylist to allowlist (http, https, mailto, tel plus relative/anchor URLs); unknown protocols are now fail-closed - Add remark-breaks to restore single-newline-to-<br> behavior that was silently dropped when replacing marked-react - Export isSafeUrl from the host module and add 16 direct unit tests covering allowed protocols, blocked schemes (javascript, data, blob, vbscript, file, custom), edge cases (empty, whitespace, mixed case) - Hoist remarkPlugins to a module-level constant to avoid per-render array allocation in the generated Sandpack component - Fix import order in generated template (shortest to longest per AGENTS.md) and remove pre-existing trailing whitespace
- urlTransform returns null (not '') for blocked URLs so react-markdown omits the href/src attribute entirely instead of producing <a href=""> - Hoist urlTransform to module-level constant alongside remarkPlugins - Add JSDoc sync-guard comments tying the exported isSafeUrl to its template-string mirror, so future maintainers know to update both - Add synchronization test asserting the embedded isSafeUrl contains the same allowlist set, URL parsing, and relative-path checks as the export
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May 11, 2026
* 🛡️ fix: Sanitize markdown artifact rendering to prevent stored XSS Replace marked-react with react-markdown + remark-gfm for artifact markdown preview. react-markdown's skipHtml strips raw HTML tags, and a urlTransform guard blocks javascript: and data: protocol links. * fix: Update useArtifactProps test to expect react-markdown dependencies * fix: Harden markdown artifact sanitization - Convert isSafeUrl from denylist to allowlist (http, https, mailto, tel plus relative/anchor URLs); unknown protocols are now fail-closed - Add remark-breaks to restore single-newline-to-<br> behavior that was silently dropped when replacing marked-react - Export isSafeUrl from the host module and add 16 direct unit tests covering allowed protocols, blocked schemes (javascript, data, blob, vbscript, file, custom), edge cases (empty, whitespace, mixed case) - Hoist remarkPlugins to a module-level constant to avoid per-render array allocation in the generated Sandpack component - Fix import order in generated template (shortest to longest per AGENTS.md) and remove pre-existing trailing whitespace * fix: Return null for blocked URLs, add sync-guard comments and test - urlTransform returns null (not '') for blocked URLs so react-markdown omits the href/src attribute entirely instead of producing <a href=""> - Hoist urlTransform to module-level constant alongside remarkPlugins - Add JSDoc sync-guard comments tying the exported isSafeUrl to its template-string mirror, so future maintainers know to update both - Add synchronization test asserting the embedded isSafeUrl contains the same allowlist set, URL parsing, and relative-path checks as the export
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Replace marked-react with react-markdown + remark-gfm for artifact markdown preview. react-markdown's skipHtml strips raw HTML tags, and a urlTransform guard blocks javascript: and data: protocol links.