diff --git a/.github/workflows/ci-pr.yaml b/.github/workflows/ci-pr.yaml
index 9b64f6c..1b049ee 100644
--- a/.github/workflows/ci-pr.yaml
+++ b/.github/workflows/ci-pr.yaml
@@ -3,6 +3,10 @@ name: Test PR
 on:
   pull_request:
 
+permissions:
+  # Read repository contents for checkout and dependency resolution only.
+  contents: read
+
 env:
   # Please make sure this version is included in the `matrix`, as the
   # `matrix` section can't use `env`, so it must be entered manually
@@ -17,7 +21,7 @@ jobs:
 
     steps:
       - name: Run nox
-        uses: frequenz-floss/gh-action-nox@v1.1.1
+        uses: frequenz-floss/gh-action-nox@80a9845a59ffc71d27b9c41099eb6cb55bc7b671 # v1.1.1
         with:
           python-version: "3.11"
           nox-session: ci_checks_max
@@ -27,15 +31,15 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Setup Git
-        uses: frequenz-floss/gh-action-setup-git@v1.0.0
+        uses: frequenz-floss/gh-action-setup-git@16952aac3ccc01d27412fe0dea3ea946530dcace # v1.0.0
 
       - name: Fetch sources
-        uses: actions/checkout@v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           submodules: true
 
       - name: Setup Python
-        uses: frequenz-floss/gh-action-setup-python-with-deps@v1.0.4
+        uses: frequenz-floss/gh-action-setup-python-with-deps@0d0d77eac3b54799f31f25a1060ef2c6ebdf9299 # v1.0.2
         with:
           python-version: ${{ env.DEFAULT_PYTHON_VERSION }}
           dependencies: .[dev-mkdocs]
@@ -44,11 +48,14 @@ jobs:
         env:
           MIKE_VERSION: gh-${{ github.job }}
         run: |
-          mike deploy $MIKE_VERSION
-          mike set-default $MIKE_VERSION
+          # mike is installed as a console script, not a runnable module.
+          # Run the installed script under isolated mode to avoid importing from
+          # the workspace when building docs from checked-out code.
+          python -I "$(command -v mike)" deploy "$MIKE_VERSION"
+          python -I "$(command -v mike)" set-default "$MIKE_VERSION"
 
       - name: Upload site
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: docs-site
           path: site/
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 2f92f66..d36f4a6 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -15,6 +15,10 @@ on:
       - "dependabot/**"
   workflow_dispatch:
 
+permissions:
+  # Read repository contents for checkout and dependency resolution only.
+  contents: read
+
 env:
   # Please make sure this version is included in the `matrix`, as the
   # `matrix` section can't use `env`, so it must be entered manually
@@ -28,7 +32,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        target:
+        platform:
           - ubuntu-24.04
           - ubuntu-24.04-arm
           - windows-latest
@@ -44,7 +48,7 @@ jobs:
           # that uses the same venv to run multiple linting sessions
           - "ci_checks_max"
           - "pytest_min"
-    runs-on: ${{ matrix.target }}
+    runs-on: ${{ matrix.platform }}
 
     steps:
       - name: Run nox
@@ -63,7 +67,9 @@ jobs:
     needs: ["nox"]
     # We skip this job only if nox was also skipped
     if: always() && needs.nox.result != 'skipped'
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
+    # Drop token permissions: this job only checks matrix status from `needs`.
+    permissions: {}
     env:
       DEPS_RESULT: ${{ needs.nox.result }}
     steps:
@@ -80,19 +86,19 @@ jobs:
           - runner: ubuntu-22.04
             target: aarch64
     steps:
-      - uses: actions/checkout@v6
-      - uses: actions/setup-python@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with:
           python-version: 3.x
       - name: Build wheels
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@e83996d129638aa358a18fbd1dfb82f0b0fb5d3b # v1.51.0
         with:
           target: ${{ matrix.platform.target }}
           args: --release --out dist --find-interpreter
           sccache: ${{ !startsWith(github.ref, 'refs/tags/') }}
           manylinux: auto
       - name: Upload wheels
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: wheels-linux-${{ matrix.platform.target }}
           path: dist
@@ -107,19 +113,19 @@ jobs:
           - runner: ubuntu-22.04
             target: aarch64
     steps:
-      - uses: actions/checkout@v6
-      - uses: actions/setup-python@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with:
           python-version: 3.x
       - name: Build wheels
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@e83996d129638aa358a18fbd1dfb82f0b0fb5d3b # v1.51.0
         with:
           target: ${{ matrix.platform.target }}
           args: --release --out dist --find-interpreter
           sccache: ${{ !startsWith(github.ref, 'refs/tags/') }}
           manylinux: musllinux_1_2
       - name: Upload wheels
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: wheels-musllinux-${{ matrix.platform.target }}
           path: dist
@@ -132,19 +138,19 @@ jobs:
           - runner: windows-latest
             target: x64
     steps:
-      - uses: actions/checkout@v6
-      - uses: actions/setup-python@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with:
           python-version: 3.x
           architecture: ${{ matrix.platform.target }}
       - name: Build wheels
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@e83996d129638aa358a18fbd1dfb82f0b0fb5d3b # v1.51.0
         with:
           target: ${{ matrix.platform.target }}
           args: --release --out dist --find-interpreter
           sccache: ${{ !startsWith(github.ref, 'refs/tags/') }}
       - name: Upload wheels
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: wheels-windows-${{ matrix.platform.target }}
           path: dist
@@ -159,18 +165,18 @@ jobs:
           - runner: macos-15
             target: aarch64
     steps:
-      - uses: actions/checkout@v6
-      - uses: actions/setup-python@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with:
           python-version: 3.x
       - name: Build wheels
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@e83996d129638aa358a18fbd1dfb82f0b0fb5d3b # v1.51.0
         with:
           target: ${{ matrix.platform.target }}
           args: --release --out dist --find-interpreter
           sccache: ${{ !startsWith(github.ref, 'refs/tags/') }}
       - name: Upload wheels
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: wheels-macos-${{ matrix.platform.target }}
           path: dist
@@ -179,14 +185,14 @@ jobs:
     name: Build source distribution packages
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
       - name: Build sdist
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@e83996d129638aa358a18fbd1dfb82f0b0fb5d3b # v1.51.0
         with:
           command: sdist
           args: --out dist
       - name: Upload sdist
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: wheels-sdist
           path: dist/*.tar.gz
@@ -236,13 +242,13 @@ jobs:
 
     steps:
       - name: Setup Git
-        uses: frequenz-floss/gh-action-setup-git@v1.0.0
+        uses: frequenz-floss/gh-action-setup-git@16952aac3ccc01d27412fe0dea3ea946530dcace # v1.0.0
 
       - name: Print environment (debug)
         run: env
 
       - name: Download package
-        uses: actions/download-artifact@v8
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           name: wheels-${{ matrix.platform.image }}-${{ matrix.platform.target }}
           path: dist
@@ -263,13 +269,13 @@ jobs:
             > pyproject.toml
 
       - name: Setup Python
-        uses: frequenz-floss/gh-action-setup-python-with-deps@v1.0.4
+        uses: frequenz-floss/gh-action-setup-python-with-deps@0d0d77eac3b54799f31f25a1060ef2c6ebdf9299 # v1.0.2
         with:
           python-version: ${{ matrix.python.semver }}
           dependencies: dist/*${{ matrix.python.wheelver }}-${{ matrix.platform.tag }}*.whl
 
       - name: Print installed packages (debug)
-        run: python -m pip freeze
+        run: python -Im pip freeze
 
   # This job runs if all the `test-installation` matrix jobs ran and succeeded.
   # It is only used to have a single job that we can require in branch
@@ -281,7 +287,9 @@ jobs:
     needs: ["test-installation"]
     # We skip this job only if test-installation was also skipped
     if: always() && needs.test-installation.result != 'skipped'
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
+    # Drop token permissions: this job only checks matrix status from `needs`.
+    permissions: {}
     env:
       DEPS_RESULT: ${{ needs.test-installation.result }}
     steps:
@@ -294,15 +302,15 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Setup Git
-        uses: frequenz-floss/gh-action-setup-git@v1.0.0
+        uses: frequenz-floss/gh-action-setup-git@16952aac3ccc01d27412fe0dea3ea946530dcace # v1.0.0
 
       - name: Fetch sources
-        uses: actions/checkout@v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           submodules: true
 
       - name: Setup Python
-        uses: frequenz-floss/gh-action-setup-python-with-deps@v1.0.4
+        uses: frequenz-floss/gh-action-setup-python-with-deps@0d0d77eac3b54799f31f25a1060ef2c6ebdf9299 # v1.0.2
         with:
           python-version: ${{ env.DEFAULT_PYTHON_VERSION }}
           dependencies: .[dev-mkdocs]
@@ -311,11 +319,14 @@ jobs:
         env:
           MIKE_VERSION: gh-${{ github.job }}
         run: |
-          mike deploy $MIKE_VERSION
-          mike set-default $MIKE_VERSION
+          # mike is installed as a console script, not a runnable module.
+          # Run the installed script under isolated mode to avoid importing from
+          # the workspace when building docs from checked-out code.
+          python -I "$(command -v mike)" deploy "$MIKE_VERSION"
+          python -I "$(command -v mike)" set-default "$MIKE_VERSION"
 
       - name: Upload site
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: docs-site
           path: site/
@@ -327,18 +338,19 @@ jobs:
     if: github.event_name == 'push'
     runs-on: ubuntu-24.04
     permissions:
+      # Push generated documentation updates to the `gh-pages` branch.
       contents: write
     steps:
       - name: Setup Git
-        uses: frequenz-floss/gh-action-setup-git@v1.0.0
+        uses: frequenz-floss/gh-action-setup-git@16952aac3ccc01d27412fe0dea3ea946530dcace # v1.0.0
 
       - name: Fetch sources
-        uses: actions/checkout@v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           submodules: true
 
       - name: Setup Python
-        uses: frequenz-floss/gh-action-setup-python-with-deps@v1.0.4
+        uses: frequenz-floss/gh-action-setup-python-with-deps@0d0d77eac3b54799f31f25a1060ef2c6ebdf9299 # v1.0.2
         with:
           python-version: ${{ env.DEFAULT_PYTHON_VERSION }}
           dependencies: .[dev-mkdocs]
@@ -351,7 +363,7 @@ jobs:
           GIT_REF: ${{ github.ref }}
           GIT_SHA: ${{ github.sha }}
         run: |
-          python -m frequenz.repo.config.cli.version.mike.info
+          python -Im frequenz.repo.config.cli.version.mike.info
 
       - name: Fetch the gh-pages branch
         if: steps.mike-version.outputs.version
@@ -372,13 +384,23 @@ jobs:
           GIT_REF: ${{ github.ref }}
           GIT_SHA: ${{ github.sha }}
         run: |
-          mike deploy --update-aliases --title "$TITLE" "$VERSION" $ALIASES
+          # Collect aliases into an array to avoid accidental (or malicious)
+          # shell injection when passing them to mike.
+          aliases=()
+          if test -n "$ALIASES"; then
+            read -r -a aliases <<<"$ALIASES"
+          fi
+          # mike is installed as a console script, not a runnable module.
+          # Run the installed script under isolated mode to avoid importing from
+          # the workspace when building docs from checked-out code.
+          python -I "$(command -v mike)" \
+            deploy --update-aliases --title "$TITLE" "$VERSION" "${aliases[@]}"
 
       - name: Sort site versions
         if: steps.mike-version.outputs.version
         run: |
           git checkout gh-pages
-          python -m frequenz.repo.config.cli.version.mike.sort versions.json
+          python -Im frequenz.repo.config.cli.version.mike.sort versions.json
           git commit -a -m "Sort versions.json"
 
       - name: Publish site
@@ -392,14 +414,12 @@ jobs:
     # Create a release only on tags creation
     if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
     permissions:
-      # We need write permissions on contents to create GitHub releases and on
-      # discussions to create the release announcement in the discussion forums
+      # Create GitHub releases and upload distribution artifacts.
       contents: write
-      discussions: write
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     steps:
       - name: Download distribution files
-        uses: actions/download-artifact@v8
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           path: dist
 
@@ -420,14 +440,14 @@ jobs:
       - name: Create GitHub release
         run: |
           set -ux
-          extra_opts=
-          if echo "$REF_NAME" | grep -- -; then extra_opts=" --prerelease"; fi
+          extra_opts=()
+          if echo "$REF_NAME" | grep -- -; then extra_opts+=(--prerelease); fi
           gh release create \
             -R "$REPOSITORY" \
             --notes-file RELEASE_NOTES.md \
             --generate-notes \
-            $extra_opts \
-            $REF_NAME \
+            "${extra_opts[@]}" \
+            "$REF_NAME" \
             dist/wheels-*/*.whl dist/wheels-sdist/*.tar.gz
         env:
           REF_NAME: ${{ github.ref_name }}
@@ -444,10 +464,10 @@ jobs:
       id-token: write
     steps:
       - name: Download distribution files
-        uses: actions/download-artifact@v8
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           path: dist
           merge-multiple: true
 
       - name: Publish the Python distribution to PyPI
-        uses: pypa/gh-action-pypi-publish@release/v1
+        uses: pypa/gh-action-pypi-publish@cef221092ed1bacb1cc03d23a2d87d1d172e277b # v1.14.0
diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 257e738..48c26d5 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -15,3 +15,10 @@
 ## Bug Fixes
 
 <!-- Here goes notable bug fixes that are worth a special mention or explanation -->
+
+## Tooling
+
+* Restored security hardening to GitHub Actions workflows: hash-pinned all
+  actions, re-added workflow-level `permissions: contents: read`, restored
+  `python -I` isolated mode on Python invocations, re-added `permissions: {}`
+  on gate jobs, and fixed shell injection risks in `mike` and release steps.