diff --git a/.github/workflows/boj-build.yml b/.github/workflows/boj-build.yml
index adf2467..2a01a08 100644
--- a/.github/workflows/boj-build.yml
+++ b/.github/workflows/boj-build.yml
@@ -36,7 +36,7 @@ jobs:
     # it actually is one instead of failing the run.
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Trigger BoJ Server (Casket/ssg-mcp)
         env:
diff --git a/.github/workflows/casket-pages.yml b/.github/workflows/casket-pages.yml
index f9a7efa..3b1ebef 100644
--- a/.github/workflows/casket-pages.yml
+++ b/.github/workflows/casket-pages.yml
@@ -22,22 +22,22 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Checkout casket-ssg
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
         with:
           repository: hyperpolymath/casket-ssg
           path: .casket-ssg
 
       - name: Setup GHCup
-        uses: haskell-actions/setup@v2.12.0
+        uses: haskell-actions/setup@6037f33647c3f17758a2356c80fc4a53d7e0685d
         with:
           ghc-version: '9.8.2'
           cabal-version: '3.10'
 
       - name: Cache Cabal
-        uses: actions/cache@v6.1.0
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9
         with:
           path: |
             ~/.cabal/packages
@@ -103,10 +103,10 @@ jobs:
           touch ../_site/.nojekyll
 
       - name: Setup Pages
-        uses: actions/configure-pages@v6.0.0
+        uses: actions/configure-pages@45bfe0192ca1faeb007ade9deae92b16b8254a0d
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v5.0.0
+        uses: actions/upload-pages-artifact@fc324d3547104276b827a68afc52ff2a11cc49c9
         with:
           path: '_site'
 
@@ -119,4 +119,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v5.0.0
+        uses: actions/deploy-pages@cd2ce8fcbc39b97be8ca5fce6e763baed58fa128
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index 6fce430..ead467e 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -37,15 +37,15 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@v4.37.7
+        uses: github/codeql-action/init@db488ddef3bf6cb639b32c2e9a7c0a7ea8271d28
         with:
           languages: ${{ matrix.language }}
           build-mode: ${{ matrix.build-mode }}
 
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v4.37.7
+        uses: github/codeql-action/analyze@db488ddef3bf6cb639b32c2e9a7c0a7ea8271d28
         with:
           category: "/language:${{ matrix.language }}"
diff --git a/.github/workflows/dogfood-gate.yml b/.github/workflows/dogfood-gate.yml
index 692d023..5626381 100644
--- a/.github/workflows/dogfood-gate.yml
+++ b/.github/workflows/dogfood-gate.yml
@@ -27,7 +27,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Check for A2ML files
         id: detect
@@ -76,7 +76,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Check for K9 files
         id: detect
@@ -126,7 +126,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Scan for invisible characters
         id: lint
@@ -190,7 +190,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Check for Groove manifest
         id: groove
@@ -250,7 +250,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Generate dogfooding scorecard
         run: |
diff --git a/.github/workflows/placement-guard.yml b/.github/workflows/placement-guard.yml
index ea9099b..7f5a2ba 100644
--- a/.github/workflows/placement-guard.yml
+++ b/.github/workflows/placement-guard.yml
@@ -26,7 +26,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
         with:
           fetch-depth: 0
 
diff --git a/.github/workflows/push-email-notify.yml b/.github/workflows/push-email-notify.yml
index 4f733f4..d33c9e5 100644
--- a/.github/workflows/push-email-notify.yml
+++ b/.github/workflows/push-email-notify.yml
@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Send push notification email
-        uses: dawidd6/action-send-mail@v3.12.0
+        uses: dawidd6/action-send-mail@94de994a9f6fffee200243214e17002e2920bb59
         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 9c24c4f..f624995 100644
--- a/.github/workflows/verify-tlaplus.yml
+++ b/.github/workflows/verify-tlaplus.yml
@@ -40,17 +40,17 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
 
       - name: Set up Eclipse Temurin 21 JRE
-        uses: actions/setup-java@v5.7.0
+        uses: actions/setup-java@dd06d9cba3e5552c54d9f8ea23572deb30010f7c
         with:
           distribution: temurin
           java-version: '21'
 
       - name: Cache tla2tools.jar
         id: cache-tla
-        uses: actions/cache@v6.1.0
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9
         with:
           path: ~/.local/share/tla2tools.jar
           key: tla2tools-v1.8.0
@@ -91,7 +91,7 @@ jobs:
 
       - name: Upload TLC logs on failure
         if: failure()
-        uses: actions/upload-artifact@v7.0.1
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a
         with:
           name: tlc-logs
           path: verisimdb/verification/proofs/tlaplus/*.log