diff --git a/apps/web/src/runtime/speaker-notes.ts b/apps/web/src/runtime/speaker-notes.ts
index 1b45572191..544e1c3b0e 100644
--- a/apps/web/src/runtime/speaker-notes.ts
+++ b/apps/web/src/runtime/speaker-notes.ts
@@ -244,15 +244,15 @@ export function buildSpeakerNotesPresenterHtml(options: {
       <button type="button" id="reset"></button>
       <div class="counter" id="counter"></div>
     </div>
-    <div class="current"><iframe id="current" title="Current slide"></iframe></div>
+    <div class="current"><iframe id="current" title="Current slide" sandbox="allow-scripts"></iframe></div>
     <div class="filmstrip">
       <section id="previous-section">
         <div class="thumb-label" id="previous-label"></div>
-        <div class="thumb-frame"><iframe id="previous" title="Previous slide"></iframe></div>
+        <div class="thumb-frame"><iframe id="previous" title="Previous slide" sandbox="allow-scripts"></iframe></div>
       </section>
       <section id="next-section">
         <div class="thumb-label" id="next-label"></div>
-        <div class="thumb-frame"><iframe id="next" title="Next slide"></iframe></div>
+        <div class="thumb-frame"><iframe id="next" title="Next slide" sandbox="allow-scripts"></iframe></div>
       </section>
     </div>
   </main>
diff --git a/apps/web/tests/runtime/speaker-notes.test.ts b/apps/web/tests/runtime/speaker-notes.test.ts
index 5384527ba3..8cf15912ad 100644
--- a/apps/web/tests/runtime/speaker-notes.test.ts
+++ b/apps/web/tests/runtime/speaker-notes.test.ts
@@ -372,4 +372,36 @@ describe('speaker notes HTML helpers', () => {
     expect(html).toContain('window.resizeTo(nextWidth, nextHeight)');
     expect(html).toContain("window.addEventListener('resize', scheduleMinimumWindowSize)");
   });
+
+  it('sandboxes the presenter slide iframes to an opaque origin', () => {
+    const html = buildSpeakerNotesPresenterHtml({
+      previewHtml: '<section class="slide">One</section>',
+      title: 'Deck',
+      projectId: 'project-1',
+      fileName: 'deck.html',
+      notes: ['Intro'],
+      initialSlideIndex: 0,
+      slideCount: 1,
+      labels: {
+        title: 'Speaker notes',
+        edit: 'Edit',
+        save: 'Save notes',
+        pause: 'Pause',
+        resume: 'Resume',
+        reset: 'Reset',
+        previous: 'Previous',
+        next: 'Next',
+        empty: 'Empty',
+        slide: 'Slide {current} / {total}',
+      },
+    });
+    // The srcdoc loaded into each frame is the full, untrusted deck (scripts
+    // included); the frames must run it in an opaque origin so it cannot reach
+    // the app's storage or daemon.
+    for (const id of ['current', 'previous', 'next']) {
+      const tag = html.match(new RegExp(`<iframe id="${id}"[^>]*>`))?.[0] ?? '';
+      expect(tag).toContain('sandbox="allow-scripts"');
+      expect(tag).not.toContain('allow-same-origin');
+    }
+  });
 });