diff --git a/.github/workflows/boj-build.yml b/.github/workflows/boj-build.yml
index e661c79f..3bbbb30b 100644
--- a/.github/workflows/boj-build.yml
+++ b/.github/workflows/boj-build.yml
@@ -37,7 +37,7 @@ jobs:
     # it actually is one instead of failing the run.
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Trigger BoJ Server (Casket/ssg-mcp)
         env:
diff --git a/.github/workflows/casket-pages.yml b/.github/workflows/casket-pages.yml
index e1b90502..92190d35 100644
--- a/.github/workflows/casket-pages.yml
+++ b/.github/workflows/casket-pages.yml
@@ -23,22 +23,22 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Checkout casket-ssg
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
           repository: hyperpolymath/casket-ssg
           path: .casket-ssg
 
       - name: Setup GHCup
-        uses: haskell-actions/setup@v2.12.0
+        uses: haskell-actions/setup@6037f33647c3f17758a2356c80fc4a53d7e0685d  # v2.12.0
         with:
           ghc-version: '9.8.2'
           cabal-version: '3.10'
 
       - name: Cache Cabal
-        uses: actions/cache@v6.1.0
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9  # v6.1.0
         with:
           path: |
             ~/.cabal/packages
@@ -104,10 +104,10 @@ jobs:
           touch ../_site/.nojekyll
 
       - name: Setup Pages
-        uses: actions/configure-pages@v6.0.0
+        uses: actions/configure-pages@45bfe0192ca1faeb007ade9deae92b16b8254a0d  # v6.0.0
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v5.0.0
+        uses: actions/upload-pages-artifact@fc324d3547104276b827a68afc52ff2a11cc49c9  # v5.0.0
         with:
           path: '_site'
 
@@ -120,4 +120,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v5.0.1
+        uses: actions/deploy-pages@368f82528645a54fb793d4d04e342629a3f51346  # v5.0.1
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index c6e092e3..05a4ede2 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -38,15 +38,15 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@v4.38.0
+        uses: github/codeql-action/init@b96794f015dfd88f77b49b1c93e0fa7110f94c63  # v4.38.0
         with:
           languages: ${{ matrix.language }}
           build-mode: ${{ matrix.build-mode }}
 
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v4.38.0
+        uses: github/codeql-action/analyze@b96794f015dfd88f77b49b1c93e0fa7110f94c63  # v4.38.0
         with:
           category: "/language:${{ matrix.language }}"
diff --git a/.github/workflows/dogfood-gate.yml b/.github/workflows/dogfood-gate.yml
index 9b439a63..85ec9aae 100644
--- a/.github/workflows/dogfood-gate.yml
+++ b/.github/workflows/dogfood-gate.yml
@@ -28,7 +28,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Check for A2ML files
         id: detect
@@ -77,7 +77,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Check for K9 files
         id: detect
@@ -127,7 +127,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Scan for invisible characters
         id: lint
@@ -191,7 +191,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Check for Groove manifest
         id: groove
@@ -251,7 +251,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Generate dogfooding scorecard
         run: |
diff --git a/.github/workflows/placement-guard.yml b/.github/workflows/placement-guard.yml
index 5813c156..8120cf41 100644
--- a/.github/workflows/placement-guard.yml
+++ b/.github/workflows/placement-guard.yml
@@ -27,7 +27,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
           fetch-depth: 0
 
diff --git a/.github/workflows/push-email-notify.yml b/.github/workflows/push-email-notify.yml
index 8a96bf98..43e0e77e 100644
--- a/.github/workflows/push-email-notify.yml
+++ b/.github/workflows/push-email-notify.yml
@@ -41,7 +41,7 @@ jobs:
     timeout-minutes: 5
     steps:
       - name: Send push notification email
-        uses: hyperpolymath/smtp-notify-action@v0.3.0
+        uses: hyperpolymath/smtp-notify-action@22e7bdb322c430c1d0dac6b3bb307f4bb139d0be  # v0.3.0
         with:
           server_address: ${{ secrets.SMTP_HOST }}
           server_port: ${{ secrets.SMTP_PORT }}
diff --git a/.github/workflows/verify-tlaplus.yml b/.github/workflows/verify-tlaplus.yml
index 8b07dc0c..eceb9026 100644
--- a/.github/workflows/verify-tlaplus.yml
+++ b/.github/workflows/verify-tlaplus.yml
@@ -41,17 +41,17 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Set up Eclipse Temurin 21 JRE
-        uses: actions/setup-java@v6.0.1
+        uses: actions/setup-java@de7274f081f381c8f8158605e0321c36c376e2e6  # v6.0.1
         with:
           distribution: temurin
           java-version: '21'
 
       - name: Cache tla2tools.jar
         id: cache-tla
-        uses: actions/cache@v6.1.0
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9  # v6.1.0
         with:
           path: ~/.local/share/tla2tools.jar
           key: tla2tools-v1.8.0
@@ -92,7 +92,7 @@ jobs:
 
       - name: Upload TLC logs on failure
         if: failure()
-        uses: actions/upload-artifact@v7.0.1
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a  # v7.0.1
         with:
           name: tlc-logs
           path: verisimdb/verification/proofs/tlaplus/*.log
diff --git a/nqc/.github/workflows/test.yml b/nqc/.github/workflows/test.yml
index 0eab5a81..d06a209a 100644
--- a/nqc/.github/workflows/test.yml
+++ b/nqc/.github/workflows/test.yml
@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
-      - uses: erlef/setup-beam@v1
+      - uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124  # v1
         with:
           otp-version: "28"
           gleam-version: "1.14.0"