For the sake of completeness I will also mention that the updated Helm chart is now also available:
registry.k8s.io/ingress-nginx/controller:v1.12.1
registry.k8s.io/ingress-nginx/controller:v1.11.5
The Helm chart has not been updated yet, but it looks like you can use the new container images by manually specifying the updated image tag in the values file: controller:
image:
tag: "v1.12.1"