diff --git a/packages/components/src/code-block/view/components/preview-panel.tsx b/packages/components/src/code-block/view/components/preview-panel.tsx
index f76a75def57..6b212289f28 100644
--- a/packages/components/src/code-block/view/components/preview-panel.tsx
+++ b/packages/components/src/code-block/view/components/preview-panel.tsx
@@ -7,6 +7,40 @@ import { keepAlive } from '../../../__internal__/keep-alive'
 
 keepAlive(h, Fragment)
 
+const SVG_NAMESPACE = 'http://www.w3.org/2000/svg'
+
+/**
+ * Creates a sanitizer that allows foreignObject only inside SVG context.
+ *
+ * Mermaid v11+ uses foreignObject for flowchart node labels, but foreignObject
+ * is a known mXSS vector (CVE-2020-26870) outside SVG context. The strategy:
+ *   1. ADD_TAGS allows foreignObject to survive DOMPurify's initial filtering
+ *   2. The uponSanitizeElement hook removes it if NOT inside an SVG element
+ *   3. HTML_INTEGRATION_POINTS lets its HTML children parse correctly
+ */
+function createSvgAwareSanitizer() {
+  const purify = DOMPurify()
+
+  const config = {
+    ADD_TAGS: ['foreignObject'],
+    ADD_ATTR: ['xmlns'],
+    HTML_INTEGRATION_POINTS: { foreignobject: true },
+  }
+
+  purify.addHook('uponSanitizeElement', (node, data) => {
+    if (data.tagName === 'foreignobject') {
+      const parent = node.parentElement
+      if (!parent || parent.namespaceURI !== SVG_NAMESPACE) {
+        node.parentNode?.removeChild(node)
+      }
+    }
+  })
+
+  return (dirty: string | Node) => purify.sanitize(dirty, config)
+}
+
+const sanitizeSvg = createSvgAwareSanitizer()
+
 type PreviewPanelProps = Pick<
   CodeBlockProps,
   'text' | 'language' | 'config'
@@ -56,7 +90,7 @@ export const PreviewPanel = defineComponent<PreviewPanelProps>({
         typeof previewContent === 'string' ||
         previewContent instanceof Element
       ) {
-        previewContainer.innerHTML = DOMPurify.sanitize(previewContent)
+        previewContainer.innerHTML = sanitizeSvg(previewContent)
       }
     })