diff --git a/Dockerfile b/Dockerfile
index c6d644c..6d02542 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.24.1
+FROM alpine:3.24.1@sha256:28bd5fe8b56d1bd048e5babf5b10710ebe0bae67db86916198a6eec434943f8b
 ARG DEBIAN_FRONTEND=noninteractive
 
 RUN apk add --update --no-cache \
diff --git a/mongodb/Dockerfile b/mongodb/Dockerfile
index 2f976f6..5e74710 100644
--- a/mongodb/Dockerfile
+++ b/mongodb/Dockerfile
@@ -1,4 +1,4 @@
-ARG BASE_TAG=latest
+ARG BASE_TAG=latest@sha256:da7505ae3308347f7faac4d9cfd384a741f8455ce67dfa77a22983b0fed99d3d
 FROM oci.bi.denbi.de/denbicloud/cron-backup:${BASE_TAG}
 
 COPY ./install-packages.sh /install-packages.sh
diff --git a/mysql/Dockerfile b/mysql/Dockerfile
index f364f9f..401fde3 100644
--- a/mysql/Dockerfile
+++ b/mysql/Dockerfile
@@ -1,4 +1,4 @@
-ARG BASE_TAG=latest
+ARG BASE_TAG=latest@sha256:da7505ae3308347f7faac4d9cfd384a741f8455ce67dfa77a22983b0fed99d3d
 FROM oci.bi.denbi.de/denbicloud/cron-backup:${BASE_TAG}
 
 COPY ./install-packages.sh /install-packages.sh
diff --git a/postgresql/Dockerfile b/postgresql/Dockerfile
index a88094c..06d91bc 100644
--- a/postgresql/Dockerfile
+++ b/postgresql/Dockerfile
@@ -1,4 +1,4 @@
-ARG BASE_TAG=latest
+ARG BASE_TAG=latest@sha256:da7505ae3308347f7faac4d9cfd384a741f8455ce67dfa77a22983b0fed99d3d
 ARG DEBIAN_FRONTEND=noninteractive
 
 FROM oci.bi.denbi.de/denbicloud/cron-backup:${BASE_TAG}