diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 000000000..ffc0bd2ce
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 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.
diff --git a/apps/web/src/lib/markdown-rich.test.tsx b/apps/web/src/lib/markdown-rich.test.tsx
index 64655ecb4..9d06cb7b6 100644
--- a/apps/web/src/lib/markdown-rich.test.tsx
+++ b/apps/web/src/lib/markdown-rich.test.tsx
@@ -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/);
   });
 });
diff --git a/apps/web/src/lib/sanitize-svg.ts b/apps/web/src/lib/sanitize-svg.ts
index a2810cb34..349367a1f 100644
--- a/apps/web/src/lib/sanitize-svg.ts
+++ b/apps/web/src/lib/sanitize-svg.ts
@@ -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 {