fix(docker): reduce Docker Scout CVEs with slim stable Nginx base

.github/workflows/docker-publish.yml

@@ -42,10 +42,67 @@ jobs:
           type=sha,prefix=sha-
           type=raw,value=latest,enable={{is_default_branch}}
 
+    # Test the same minimal HTTP-only Docker application; no TLS setup is added.
+    - name: Build fresh Docker image for security testing
+      run: docker build --pull -t markdown-viewer:security-audit .
+
+    - name: Smoke-test HTTP application and Nginx configuration
+      run: |
+        docker run -d --rm --name mdv-security-test -p 127.0.0.1:18080:80 markdown-viewer:security-audit
+        trap 'docker stop mdv-security-test >/dev/null 2>&1 || true' EXIT
+        docker exec mdv-security-test nginx -t
+        for i in $(seq 1 30); do
+          if curl -fsS --max-time 3 -o /dev/null http://127.0.0.1:18080/; then break; fi
+          sleep 1
+        done
+        curl -fsS --max-time 10 -o /dev/null http://127.0.0.1:18080/
+        curl -fsS --max-time 10 -o /dev/null http://127.0.0.1:18080/styles.css
+        curl -fsS --max-time 10 -o /dev/null http://127.0.0.1:18080/script.js
+        curl -fsSI --max-time 10 http://127.0.0.1:18080/ | grep -qi '^content-security-policy:'
+        ! curl -fsSI --max-time 10 http://127.0.0.1:18080/ | grep -qi 'upgrade-insecure-requests'
+
+    - name: Prepare Docker vulnerability report directory
+      run: mkdir -p docker-artifacts
+
+    - name: Scan all known OS and library CVEs (machine-readable artifact)
+      uses: aquasecurity/trivy-action@v0.36.0
+      with:
+        image-ref: markdown-viewer:security-audit
+        format: json
+        output: docker-artifacts/trivy-vulnerabilities.json
+        scanners: vuln
+        vuln-type: os,library
+        severity: UNKNOWN,LOW,MEDIUM,HIGH,CRITICAL
+        exit-code: '0'
+
+    - name: Fail on fixable critical or high vulnerabilities
+      uses: aquasecurity/trivy-action@v0.36.0
+      with:
+        image-ref: markdown-viewer:security-audit
+        format: table
+        scanners: vuln
+        vuln-type: os,library
+        severity: CRITICAL,HIGH
+        ignore-unfixed: true
+        exit-code: '1'
+
+    - name: Upload complete vulnerability scan report
+      if: always()
+      uses: actions/upload-artifact@v4
+      with:
+        name: docker-security-report
+        path: docker-artifacts/trivy-vulnerabilities.json
+        if-no-files-found: ignore
+
     - name: Build and push Docker image
       uses: docker/build-push-action@v5
       with:
         context: .
+        pull: true
+        # Registry-published images carry provenance and an SBOM attestation.
+        # Local Docker image-store scans do not inherit registry attestations.
+        provenance: mode=max
+        sbom: true
         push: ${{ github.event_name != 'pull_request' }}
         tags: ${{ steps.meta.outputs.tags }}
         labels: ${{ steps.meta.outputs.labels }}

Dockerfile

@@ -1,5 +1,9 @@
 # Use nginx as the base image for serving static files
-FROM nginx:alpine
+FROM nginx:1.31.8-alpine3.24-slim
+
+# Omit optional Alpine/Nginx modules to reduce third-party package exposure.
+# Apply security updates from the supported Alpine stable release.
+RUN apk upgrade --no-cache
 
 # PERF-019: Only copy necessary web files (exclude .git, desktop-app, wiki, etc.)
 COPY index.html /usr/share/nginx/html/