diff --git a/packages/@glimmer-workspace/integration-tests/test/attributes-test.ts b/packages/@glimmer-workspace/integration-tests/test/attributes-test.ts
index eef13f25c13..51ea7d96fba 100644
--- a/packages/@glimmer-workspace/integration-tests/test/attributes-test.ts
+++ b/packages/@glimmer-workspace/integration-tests/test/attributes-test.ts
@@ -144,6 +144,25 @@ export class AttributesTests extends RenderTest {
     this.assertStableNodes();
   }
 
+  @test
+  'svg a[href] is marked as unsafe (sanitization is not namespace-dependent)'() {
+    // SVG-namespaced elements preserve their authored (lowercase) tag name, so
+    // `element.tagName` is `'a'` rather than the `'A'` an HTML anchor reports.
+    // URL sanitization must still apply, otherwise `<svg><a href>` is an XSS
+    // bypass for the same `javascript:` URLs that are blocked on `<a href>`.
+    this.render('<svg><a href="{{this.foo}}"></a></svg>', { foo: 'javascript:foo()' });
+    this.assertHTML('<svg><a href="unsafe:javascript:foo()"></a></svg>');
+    this.assertStableRerender();
+
+    this.rerender({ foo: 'http://foo.bar' });
+    this.assertHTML('<svg><a href="http://foo.bar"></a></svg>');
+    this.assertStableNodes();
+
+    this.rerender({ foo: 'javascript:foo()' });
+    this.assertHTML('<svg><a href="unsafe:javascript:foo()"></a></svg>');
+    this.assertStableNodes();
+  }
+
   @test
   'triple curlies in attribute position'() {
     this.render('<div data-bar="bar" data-foo={{{this.rawString}}}>Hello</div>', {
diff --git a/packages/@glimmer/runtime/lib/dom/sanitized-values.ts b/packages/@glimmer/runtime/lib/dom/sanitized-values.ts
index a5203749453..9c4dc5a67aa 100644
--- a/packages/@glimmer/runtime/lib/dom/sanitized-values.ts
+++ b/packages/@glimmer/runtime/lib/dom/sanitized-values.ts
@@ -26,7 +26,14 @@ function checkDataURI(tagName: Nullable<string>, attribute: string): boolean {
 }
 
 export function requiresSanitization(tagName: string, attribute: string): boolean {
-  return checkURI(tagName, attribute) || checkDataURI(tagName, attribute);
+  // `badTags`/`badTagsForDataURI` are listed in the uppercase form that HTML
+  // elements report from `tagName`. Elements in other namespaces (e.g. an SVG
+  // `<a href>`) preserve their authored case, so `element.tagName` is `'a'`
+  // rather than `'A'`. Normalize here so the build-time gate matches what
+  // `sanitizeAttributeValue` already does, and the URL sanitization control
+  // can't be bypassed simply by living in the SVG namespace.
+  const upperTagName = tagName.toUpperCase();
+  return checkURI(upperTagName, attribute) || checkDataURI(upperTagName, attribute);
 }
 
 interface NodeUrlParseResult {