diff --git a/app/Dockerfile b/app/Dockerfile
index dc3de69..c31cd73 100644
--- a/app/Dockerfile
+++ b/app/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.9
+FROM alpine:3.23@sha256:51183f2cfa6320055da30872f211093f9ff1d3cf06f39a0bdb212314c5dc7375
 ADD app /
 ADD index.html.tmpl /
 EXPOSE 80