RenderFrameHost* ChildFrameAt(RenderFrameHost* frame, size_t index) {
  RenderFrameHostImpl* rfh = static_cast<RenderFrameHostImpl*>(frame);
  if (index >= rfh->frame_tree_node()->child_count())
    return nullptr;
  return rfh->frame_tree_node()->child_at(index)->current_frame_host();
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.