diff --git a/.github/workflows/codeql-analysis.yml b/.github/workflows/codeql-analysis.yml
index f6a88f0..6423654 100644
--- a/.github/workflows/codeql-analysis.yml
+++ b/.github/workflows/codeql-analysis.yml
@@ -39,10 +39,10 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3
       # Initializes the CodeQL tools for scanning.
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@v2
+        uses: github/codeql-action/init@b8d3b6e8af63cde30bdc382c0bc28114f4346c88 # v2
         with:
           languages: ${{ matrix.language }}
           # If you wish to specify custom queries, you can do so here or in a config file.
@@ -55,7 +55,7 @@ jobs:
       # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
       # If this step fails, then you should remove it and run the build manually (see below)
       - name: Autobuild
-        uses: github/codeql-action/autobuild@v2
+        uses: github/codeql-action/autobuild@b8d3b6e8af63cde30bdc382c0bc28114f4346c88 # v2
 
       # ℹ️ Command-line programs to run using the OS shell.
       # 📚 See https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstepsrun
@@ -67,4 +67,4 @@ jobs:
       #   echo "Run, Build Application using script"
       #   ./location_of_script_within_repo/buildscript.sh
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v2
+        uses: github/codeql-action/analyze@b8d3b6e8af63cde30bdc382c0bc28114f4346c88 # v2
diff --git a/.github/workflows/pypi-publish.yml b/.github/workflows/pypi-publish.yml
index 0d70d1e..63fe4df 100644
--- a/.github/workflows/pypi-publish.yml
+++ b/.github/workflows/pypi-publish.yml
@@ -11,8 +11,8 @@ jobs:
       id-token: write
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: '3.11'
           cache: 'pip'
diff --git a/taskcluster/docker/fetch/Dockerfile b/taskcluster/docker/fetch/Dockerfile
index a8002cf..0fc5cb7 100644
--- a/taskcluster/docker/fetch/Dockerfile
+++ b/taskcluster/docker/fetch/Dockerfile
@@ -1,4 +1,4 @@
-FROM debian:11
+FROM debian:11@sha256:8a08b2875ed17adc464ae03cf5f8652a41821fb8d3d2b17923f11e7489b146da
 
 ### Add worker user and setup its workspace.
 RUN mkdir /builds && \
diff --git a/taskcluster/docker/python/Dockerfile b/taskcluster/docker/python/Dockerfile
index 64fc59d..f3cfe37 100644
--- a/taskcluster/docker/python/Dockerfile
+++ b/taskcluster/docker/python/Dockerfile
@@ -2,7 +2,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-FROM debian:bookworm-slim
+FROM debian:bookworm-slim@sha256:56ff6d36d4eb3db13a741b342ec466f121480b5edded42e4b7ee850ce7a418ee
 LABEL maintainer="Mozilla Release Engineering <release@mozilla.com>"
 
 VOLUME /builds/worker/checkouts