diff --git a/.github/scripts/verify-release_workflow_pins.sh b/.github/scripts/verify-release_workflow_pins.sh
new file mode 100755
index 00000000..3daea2c8
--- /dev/null
+++ b/.github/scripts/verify-release_workflow_pins.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+readonly workflow_files=(
+  ".github/workflows/release.yml"
+  ".github/workflows/release-bazel.yml"
+  ".github/workflows/python.yml"
+)
+
+status=0
+
+for file in "${workflow_files[@]}"; do
+  while read -r line_no ref; do
+    if [[ "$ref" == ./* ]] || [[ "$ref" == docker://* ]]; then
+      continue
+    fi
+
+    if [[ ! "$ref" =~ @[0-9a-f]{40}$ ]]; then
+      printf 'Mutable GitHub Actions ref in %s:%s -> %s\n' "$file" "$line_no" "$ref" >&2
+      status=1
+    fi
+  done < <(awk '
+    match($0, /^[[:space:]-]*uses:[[:space:]]*([^[:space:]#]+)/, m) {
+      print NR, m[1]
+    }
+  ' "$file")
+done
+
+exit "$status"
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4b9513e4..4f59f68f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,6 +7,12 @@ on:
 permissions:
   contents: read
 jobs:
+  release-workflow-policy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # actions/checkout v4.2.2
+      - run: .github/scripts/verify-release_workflow_pins.sh
+        shell: bash
   build-appleclang:
     runs-on: macos-latest
     strategy:
diff --git a/.github/workflows/python.yml b/.github/workflows/python.yml
index 55aee2c8..f1458079 100644
--- a/.github/workflows/python.yml
+++ b/.github/workflows/python.yml
@@ -37,11 +37,11 @@ jobs:
       # Bazel fails if the username is unknown.
       USER: runner
     steps:
-      - uses: actions/checkout@v4.2.2
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # actions/checkout v4.2.2
       # Stash the timestamp for the commit SHA that triggered the workflow.
       - run: echo "timestamp=$(git log -1 --pretty=%ct)" >> "${GITHUB_ENV}"
         shell: bash
-      - uses: bazel-contrib/setup-bazel@0.15.0
+      - uses: bazel-contrib/setup-bazel@4fd964a13a440a8aeb0be47350db2fc640f19ca8 # bazel-contrib/setup-bazel 0.15.0
         with:
           bazelisk-version: '1.x'
       - name: Prepare Python ${{ matrix.ver }} environment
@@ -69,7 +69,7 @@ jobs:
           "${PYTHON}" re2_test.py
         shell: bash
         working-directory: python
-      - uses: actions/upload-artifact@v4.6.2
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # actions/upload-artifact v4.6.2
         with:
           name: ${{ hashFiles('python/google_re2-*.whl') }}
           path: python/google_re2-*.whl
@@ -98,14 +98,14 @@ jobs:
       # Otherwise, Python refuses to install the built wheel!
       SYSTEM_VERSION_COMPAT: 0
     steps:
-      - uses: actions/checkout@v4.1.7
+      - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # actions/checkout v4.1.7
       # Stash the timestamp for the commit SHA that triggered the workflow.
       - run: echo "timestamp=$(git log -1 --pretty=%ct)" >> "${GITHUB_ENV}"
         shell: bash
-      - uses: bazel-contrib/setup-bazel@0.15.0
+      - uses: bazel-contrib/setup-bazel@4fd964a13a440a8aeb0be47350db2fc640f19ca8 # bazel-contrib/setup-bazel 0.15.0
         with:
           bazelisk-version: '1.x'
-      - uses: actions/setup-python@v5.6.0
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # actions/setup-python v5.6.0
         with:
           python-version: ${{ matrix.ver }}
       - name: Prepare Python ${{ matrix.ver }} environment
@@ -134,7 +134,7 @@ jobs:
           python re2_test.py
         shell: bash
         working-directory: python
-      - uses: actions/upload-artifact@v4.6.2
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # actions/upload-artifact v4.6.2
         with:
           name: ${{ hashFiles('python/google_re2-*.whl') }}
           path: python/google_re2-*.whl
@@ -160,11 +160,11 @@ jobs:
       BAZEL_CPU: ${{ matrix.arch.bazel-name }}_windows
       PLAT_NAME: ${{ matrix.arch.python-name }}
     steps:
-      - uses: actions/checkout@v4.2.2
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # actions/checkout v4.2.2
       # Stash the timestamp for the commit SHA that triggered the workflow.
       - run: echo "timestamp=$(git log -1 --pretty=%ct)" >> "${GITHUB_ENV}"
         shell: bash
-      - uses: bazel-contrib/setup-bazel@0.15.0
+      - uses: bazel-contrib/setup-bazel@4fd964a13a440a8aeb0be47350db2fc640f19ca8 # bazel-contrib/setup-bazel 0.15.0
         with:
           bazelisk-version: '1.x'
       # Lowercase the architecture name for `actions/setup-python`.
@@ -172,7 +172,7 @@ jobs:
           ARCHITECTURE=${{ matrix.arch.name }}
           echo "architecture=${ARCHITECTURE,,}" >> "${GITHUB_ENV}"
         shell: bash
-      - uses: actions/setup-python@v5.6.0
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # actions/setup-python v5.6.0
         with:
           python-version: ${{ matrix.ver }}
           architecture: ${{ env.architecture }}
@@ -201,7 +201,7 @@ jobs:
           python re2_test.py
         shell: bash
         working-directory: python
-      - uses: actions/upload-artifact@v4.6.2
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # actions/upload-artifact v4.6.2
         with:
           name: ${{ hashFiles('python/google_re2-*.whl') }}
           path: python/google_re2-*.whl
@@ -217,11 +217,11 @@ jobs:
       id-token: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4.2.2
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # actions/checkout v4.2.2
       # Stash the timestamp for the commit SHA that triggered the workflow.
       - run: echo "timestamp=$(git log -1 --pretty=%ct)" >> "${GITHUB_ENV}"
         shell: bash
-      - uses: actions/setup-python@v5.6.0
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # actions/setup-python v5.6.0
         with:
           python-version: '3.x'
       - name: Prepare Python 3.x environment
@@ -237,7 +237,7 @@ jobs:
           python -m build --sdist
         shell: bash
         working-directory: python
-      - uses: actions/download-artifact@v4.3.0
+      - uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # actions/download-artifact v4.3.0
         with:
           path: python
       - name: Set build number to ${{ inputs.build }}
@@ -253,6 +253,6 @@ jobs:
         shell: bash
         working-directory: python
       - if: inputs.build >= 1
-        uses: pypa/gh-action-pypi-publish@v1.13.0
+        uses: pypa/gh-action-pypi-publish@ed0c53931b1dc9bd32cbe73a98c7f6766f8a527e # pypa/gh-action-pypi-publish v1.13.0
         with:
           packages-dir: python/dist
diff --git a/.github/workflows/release-bazel.yml b/.github/workflows/release-bazel.yml
index 16a0fcfc..8a5f3959 100644
--- a/.github/workflows/release-bazel.yml
+++ b/.github/workflows/release-bazel.yml
@@ -18,7 +18,7 @@ on:
         required: true
 jobs:
   release:
-    uses: bazel-contrib/publish-to-bcr/.github/workflows/publish.yaml@v0.2.2
+    uses: bazel-contrib/publish-to-bcr/.github/workflows/publish.yaml@096e4724c760aa0024916fe772701c06926f4c49 # bazel-contrib/publish-to-bcr v0.2.2
     with:
       draft: false
       tag_name: ${{ inputs.tag_name }}
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index fd803d4c..783c503e 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -16,7 +16,7 @@ jobs:
     env:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - uses: actions/checkout@v4.2.2
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # actions/checkout v4.2.2
       - run: |
           gh release create "${GITHUB_REF_NAME}" \
             --generate-notes --latest --verify-tag \
@@ -28,7 +28,7 @@ jobs:
             --archive zip \
             --repo "${GITHUB_REPOSITORY}"
         shell: bash
-      - uses: sigstore/gh-action-sigstore-python@v3.0.1
+      - uses: sigstore/gh-action-sigstore-python@f7ad0af51a5648d09a20d00370f0a91c3bdf8f84 # sigstore/gh-action-sigstore-python v3.0.1
         with:
           # N.B. This is a whitespace-separated string!
           inputs: '*.tar.gz *.zip'