diff --git a/app/Dockerfile b/app/Dockerfile
index dc3de69..763e87d 100644
--- a/app/Dockerfile
+++ b/app/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.9
+FROM alpine:3.23@sha256:865b95f46d98cf867a156fe4a135ad3fe50d2056aa3f25ed31662dff6da4eb62
 ADD app /
 ADD index.html.tmpl /
 EXPOSE 80