diff --git a/Dockerfile b/Dockerfile
index df7697b2..eb5a7ec8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 # hadolint ignore=DL3007
-FROM myoung34/github-runner-base:latest
+FROM myoung34/github-runner-base:latest@sha256:b666eb826ae134db08b070578aba2e4ce25e539a1cab1a7c62b4b10118d6936e
 LABEL maintainer="myoung34@my.apsu.edu"
 
 ENV AGENT_TOOLSDIRECTORY=/opt/hostedtoolcache
diff --git a/Dockerfile.base b/Dockerfile.base
index 76744425..e5e2933a 100644
--- a/Dockerfile.base
+++ b/Dockerfile.base
@@ -1,4 +1,4 @@
-FROM ubuntu:focal
+FROM ubuntu:focal@sha256:8feb4d8ca5354def3d8fce243717141ce31e2c428701f6682bd2fafe15388214
 LABEL maintainer="myoung34@my.apsu.edu"
 
 ARG DUMB_INIT_VERSION="1.2.2"