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🛡️ Sentinel: [HIGH] Fix mXSS vulnerabilities in manual SVG sanitization #227

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Merged
bobdivx merged 1 commit into from
Oct 13, 2026
Merged

🛡️ Sentinel: [HIGH] Fix mXSS vulnerabilities in manual SVG sanitization #227

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4 changes: 4 additions & 0 deletions .jules/sentinel.md
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## 2026-10-12 - [Improved SVG Sanitization against mXSS]
**Vulnerability:** The manual SVG sanitizer `apps/web/src/lib/sanitize-svg.ts` used an insufficient allowlist/blocklist. It allowed `<foreignObject>`, `<use>`, `<animate>`, `<set>`, `<image>`, and `<math>` which could lead to mutation XSS (mXSS) and other attack vectors when rendering untrusted Mermaid or Math blocks.
**Learning:** Manual DOM tree sanitization is notoriously hard to get right because attackers can hide active elements (e.g. `<a>` tags with `javascript:` payloads) inside grandchild trees (like `<math><mtext><a>`) or use SVG-specific tricks (like `<animate href... values="javascript:...">`) which naive list-based cleaners overlook.
**Prevention:** Rather than adding heavy third-party dependencies (like DOMPurify) against explicit project instructions, expanding the `BLOCKED` Set to include these structural injection vectors provides a robust, zero-dependency mitigation. Future expansions should verify nested elements carefully.
3 changes: 1 addition & 2 deletions apps/web/src/lib/markdown-rich.test.tsx
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Expand Up @@ -72,7 +72,6 @@ describe('Markdown riche (P5-01)', () => {

it('sanitizeSvg retire scripts et gestionnaires', () => {
const out = sanitizeSvg('<svg><script>x</script><rect onload="x" style="fill:url(javascript:x)" /><image href="https://e.x/a.png"/></svg>');
expect(out).not.toMatch(/script|onload|javascript/);
expect(out).toContain('href="https://e.x/a.png"');
expect(out).not.toMatch(/script|onload|javascript|image/);
});
});
2 changes: 1 addition & 1 deletion apps/web/src/lib/sanitize-svg.ts
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Expand Up @@ -2,7 +2,7 @@
* Nettoyage défensif d'un SVG produit par mermaid (déjà en `securityLevel: 'strict'`) :
* pas de script, pas de gestionnaire `on*`, pas de lien hors ancre/http(s).
*/
const BLOCKED = new Set(['script', 'iframe', 'object', 'embed', 'link', 'meta', 'base', 'form', 'input', 'textarea', 'button']);
const BLOCKED = new Set(['script', 'iframe', 'object', 'embed', 'link', 'meta', 'base', 'form', 'input', 'textarea', 'button', 'foreignobject', 'use', 'animate', 'set', 'image', 'math']);
const SAFE_LINK = /^(#|https?:\/\/)/i;

export function sanitizeSvg(svg: string): string {
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