diff --git a/app/Dockerfile b/app/Dockerfile
index dc3de69..a452fb8 100644
--- a/app/Dockerfile
+++ b/app/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.9
+FROM alpine:3.23@sha256:25109184c71bdad752c8312a8623239686a9a2071e8825f20acb8f2198c3f659
 ADD app /
 ADD index.html.tmpl /
 EXPOSE 80