diff --git a/.github/workflows/claude-pr-review.yml b/.github/workflows/claude-pr-review.yml
index 28590db..08c6c79 100644
--- a/.github/workflows/claude-pr-review.yml
+++ b/.github/workflows/claude-pr-review.yml
@@ -13,7 +13,6 @@ jobs:
       contents: write
       pull-requests: write
       issues: write
-      id-token: write
     steps:
       - name: Check out PR head commit
         uses: actions/checkout@v4
@@ -22,7 +21,7 @@ jobs:
           fetch-depth: 0
 
       - name: Run Claude on the review feedback
-        uses: anthropics/claude-code-action@v1
+        uses: anthropics/claude-code-action@428971d2ecd6e3a7cb0ee0da2a3a8b33fdb3678d # v1
         with:
           anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           prompt: |
diff --git a/tests/test_workflows_security.py b/tests/test_workflows_security.py
new file mode 100644
index 0000000..3bec515
--- /dev/null
+++ b/tests/test_workflows_security.py
@@ -0,0 +1,22 @@
+"""Security regression tests for GitHub Actions workflows."""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+WORKFLOW = Path(".github/workflows/claude-pr-review.yml")
+
+
+def test_claude_pr_review_uses_immutable_action_pin() -> None:
+    workflow = WORKFLOW.read_text()
+
+    match = re.search(r"uses:\s*anthropics/claude-code-action@([0-9a-f]{40})\b", workflow)
+
+    assert match is not None
+
+
+def test_claude_pr_review_does_not_request_oidc_token() -> None:
+    workflow = WORKFLOW.read_text()
+
+    assert not re.search(r"^\s*id-token:\s*write\s*$", workflow, re.MULTILINE)