feat: show Arch column only when multiple architectures are scanned

Reviewed-on: #10
Reviewed-by: LLMReview <27+autoreview@noreplay.horstenkamp.eu>

README.md

@@ -6,9 +6,9 @@ A self-contained Gitea and GitHub Actions composite action that extracts multi-p
 
 ## ✨ Features
 
-- **Multi-Platform Support**: Automatically detects and extracts SPDX SBOM attestations for multi arch images.
-- **Fast Attestation Extraction**: Uses `docker buildx imagetools inspect` to extract SBOMs directly from registry manifest indices in seconds without downloading layer blobs.
-- **Graceful Fallbacks**: If SBOM attestations or baseline images are missing, automatically falls back to generating SBOMs directly with Trivy. Using images that do contain an SBOM is highly recomended though!
+- **Dynamic Multi-Platform Support**: Automatically discovers and scans all architectures present in container images, or iterates over an explicit list of target architectures.
+- **Fast Attestation Extraction**: Uses `docker buildx imagetools inspect` to extract platform-specific SBOMs directly from registry manifest indices in seconds without downloading layer blobs.
+- **Graceful Fallbacks**: If SBOM attestations are missing for any platform, automatically falls back to generating SBOMs directly with Trivy per architecture.
 - **Set-Based Differential Analysis**: Categorizes vulnerabilities into:
   - 🔴 **Introduced Vulnerabilities** (newly added in this branch / commit)
   - 🟢 **Fixed Vulnerabilities** (present in target baseline, resolved in this branch)
@@ -20,13 +20,15 @@ A self-contained Gitea and GitHub Actions composite action that extracts multi-p
 ## 📥 Inputs
 
 | Input | Description | Required | Default |
-| :--- | :--- | :---: | :--- |
+| :--- | :--- | :--- | :--- |
 | `head-image` | Head container image reference to scan (e.g. `registry.example.com/repo:git-sha`) | **Yes** | — |
 | `target-image` | Target baseline container image reference to compare against (e.g. `registry.example.com/repo:latest`) | **Yes** | — |
 | `target-branch` | Target branch name for report headings | No | `main` |
+| `architectures` | Comma-separated architectures/platforms to scan (e.g. `amd64,arm64`). If omitted, scans all architectures present in the image. | No | _(all)_ |
 | `output-delta` | Output path for the CVE delta Markdown report | No | `cve-delta.md` |
 | `output-summary` | Output path for the full vulnerability Markdown summary | No | `cve-summary.md` |
 | `write-summary` | Whether to append the generated reports to the job summary (`$GITHUB_STEP_SUMMARY`) | No | `true` |
+| `use-inbuild-sbom` | Whether to inspect and use built-in image SBOM attestations. If false, generates SBOMs directly with Trivy | No | `false` |
 
 ---
 
@@ -39,6 +41,31 @@ A self-contained Gitea and GitHub Actions composite action that extracts multi-p
 
 ---
 
+## 🔍 Built-in SBOM Attestations vs. Trivy Direct Scanning (Syft vs. Trivy)
+
+This action supports two modes for obtaining SBOMs:
+
+### 1. Direct Image Scanning with Trivy (`use-inbuild-sbom: false` — Default & Recommended)
+By default, the action uses `trivy image --format spdx-json` to generate the SBOM directly from the container images:
+- **Full Filesystem Fidelity**: Inspects the entire flattened root filesystem, reading `/etc/os-release` and native package databases (e.g. `/var/lib/dpkg/status`, RPM databases, apk).
+- **Accurate OS & Language Package Detection**: Successfully catalogs both OS packages (Debian, Alpine, RHEL, etc.) and application dependencies (Python, Node.js, Go, etc.).
+- **Symmetric, Apples-to-Apples Comparisons**: Both `head` and `target` images are analyzed using the identical Trivy engine and vulnerability database, preventing skewed diffs.
+
+### 2. Built-in Attestation Extraction (`use-inbuild-sbom: true`)
+When enabled, the action extracts SBOM attestations attached to the container image using `docker buildx imagetools inspect`:
+- **Speed**: Extracts the SBOM JSON metadata directly from the registry manifest index in seconds without pulling image layer blobs.
+- **Underlying Generator (Syft)**: Docker Buildx (`sbom: true`) uses BuildKit's embedded Syft scanner (`moby/buildkit-syft-scanner`).
+- **Known Limitations with Trivy**:
+  - **Testing/Rolling Distributions**: Embedded Syft versions may not recognize newer or unreleased distributions (such as Debian 13 "Trixie"), recording the OS as `family="none"` and skipping OS package vulnerability matching.
+  - **Multi-Stage Builds**: Analyzing layer diffs rather than the flattened container rootfs can cause package database paths to be omitted or detached from the OS manifest.
+  - **Schema/PURL Discrepancies**: Syft and Trivy express certain package qualifiers and namespaces differently in SPDX. When Trivy scans a Syft SPDX file that lacks explicit distro qualifiers, Trivy will silently skip OS vulnerability checks.
+  - **Differential Skew**: If a `head` image uses an incomplete Syft SBOM (detecting only language packages) while `target` is scanned directly with Trivy (detecting 400+ OS packages), the differential report will erroneously show hundreds of "resolved" CVEs.
+
+> [!TIP]
+> If your builds run on stable base images where BuildKit's Syft scanner accurately captures all OS packages, you can set `use-inbuild-sbom: 'true'` to speed up CI runs. Otherwise, leave it as `false` to ensure consistent and comprehensive scans.
+
+---
+
 ## 🚀 Usage Example
 
 ```yaml
@@ -52,7 +79,6 @@ jobs:
         with:
           context: .
           push: true
-          sbom: true
           tags: registry.example.com/my-app:git-${{ github.sha }}
 
       - name: Compare Vulnerabilities (Head vs Target)

action.yaml

@@ -12,6 +12,10 @@ inputs:
     description: Target branch name for delta heading (e.g. main)
     required: false
     default: main
+  architectures:
+    description: Comma-separated list of architectures or platforms to scan (e.g. 'amd64,arm64' or 'linux/amd64,linux/arm64'). If empty, scans all architectures found in the container image.
+    required: false
+    default: ''
   output-delta:
     description: Output markdown file for CVE delta report
     required: false
@@ -24,6 +28,10 @@ inputs:
     description: Whether to append the generated reports to the job summary ($GITHUB_STEP_SUMMARY)
     required: false
     default: 'true'
+  use-inbuild-sbom:
+    description: Whether to inspect and use built-in image SBOM attestations. If false, generates SBOM directly from images with Trivy.
+    required: false
+    default: 'false'
 
 outputs:
   delta-report:
@@ -58,14 +66,15 @@ runs:
   - name: Install and Verify Trivy
     shell: bash
     run: |
-      mkdir -p "$HOME/.cache/trivy-bin" "$HOME/.local/bin"
-      echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+      set -euo pipefail
 
-      ARCH=$(uname -m)
-      case "$ARCH" in
+      mkdir -p "$HOME/.local/bin" "$HOME/.cache/trivy-bin"
+      echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+      ARCH="$(uname -m)"
+      case "${ARCH}" in
         x86_64) T_ARCH="64bit" ;;
         aarch64|arm64) T_ARCH="ARM64" ;;
-        *) echo "Unsupported architecture: $ARCH"; exit 1 ;;
+        *) echo "::error::Unsupported architecture: ${ARCH}"; exit 1 ;;
       esac
 
       checksums_file="${{ github.action_path }}/checksums.txt"
@@ -86,108 +95,327 @@ runs:
     shell: bash
     run: |
       export PATH="$HOME/.local/bin:$PATH"
+      export TRIVY_SKIP_VERSION_CHECK="true"
       mkdir -p sboms/head sboms/target
 
       cleanup_file() {
         local f="$1"
-        if [ ! -s "$f" ] || [ "$(cat "$f" 2>/dev/null)" = "null" ]; then
-          rm -f "$f"
+        if [ -f "$f" ]; then
+          if [ ! -s "$f" ] || [ "$(cat "$f" 2>/dev/null)" = "null" ]; then
+            rm -f "$f"
+          fi
         fi
       }
 
-      # Extract platform SBOMs for head image
-      echo "Extracting platform SBOMs for head image: ${{ inputs.head-image }}..."
-      docker buildx imagetools inspect "${{ inputs.head-image }}" \
-        --format '{{ json (index .SBOM "linux/amd64").SPDX }}' > sboms/head/sbom-amd64.spdx.json 2>/dev/null || true
-      cleanup_file sboms/head/sbom-amd64.spdx.json
+      head_sbom_err=""
+      target_sbom_err=""
+      use_inbuild="${{ inputs.use-inbuild-sbom }}"
 
-      docker buildx imagetools inspect "${{ inputs.head-image }}" \
-        --format '{{ json (index .SBOM "linux/arm64").SPDX }}' > sboms/head/sbom-arm64.spdx.json 2>/dev/null || true
-      cleanup_file sboms/head/sbom-arm64.spdx.json
+      # Determine target platforms / architectures
+      PLATFORMS=()
+      if [ -n "${{ inputs.architectures }}" ]; then
+        IFS=',' read -ra RAW_ARCHS <<< "${{ inputs.architectures }}"
+        for a in "${RAW_ARCHS[@]}"; do
+          clean_a=$(echo "$a" | xargs)
+          [ -z "$clean_a" ] && continue
+          if [[ "$clean_a" != *"/"* ]]; then
+            PLATFORMS+=("linux/${clean_a}")
+          else
+            PLATFORMS+=("$clean_a")
+          fi
+        done
+      else
+        echo "Auto-discovering architectures from images..."
+        raw_head=$(docker buildx imagetools inspect --raw "${{ inputs.head-image }}" 2>/dev/null || true)
+        raw_target=$(docker buildx imagetools inspect --raw "${{ inputs.target-image }}" 2>/dev/null || true)
 
-      # If single-arch, extract root .SPDX
-      if [ ! -f sboms/head/sbom-amd64.spdx.json ] && [ ! -f sboms/head/sbom-arm64.spdx.json ]; then
-        docker buildx imagetools inspect "${{ inputs.head-image }}" \
-          --format '{{ json .SBOM.SPDX }}' > sboms/head/sbom-amd64.spdx.json 2>/dev/null || true
-        cleanup_file sboms/head/sbom-amd64.spdx.json
+        discovered=$(node -e '
+          const raw1 = process.argv[1];
+          const raw2 = process.argv[2];
+          const set = new Set();
+          for (const raw of [raw1, raw2]) {
+            if (!raw) continue;
+            try {
+              const data = JSON.parse(raw);
+              const manifests = data.manifests || [];
+              for (const m of manifests) {
+                if (m.platform && m.platform.architecture && m.platform.architecture !== "unknown") {
+                  const os = m.platform.os || "linux";
+                  const variant = m.platform.variant ? "/" + m.platform.variant : "";
+                  set.add(`${os}/${m.platform.architecture}${variant}`);
+                }
+              }
+            } catch (e) {}
+          }
+          console.log(Array.from(set).sort().join("\n"));
+        ' "$raw_head" "$raw_target")
+
+        if [ -n "$discovered" ]; then
+          while IFS= read -r line; do
+            [ -n "$line" ] && PLATFORMS+=("$line")
+          done <<< "$discovered"
+        fi
       fi
 
-      # Fallback to generating head SBOM with Trivy if attestation missing
-      if [ ! -f sboms/head/sbom-amd64.spdx.json ] && [ ! -f sboms/head/sbom-arm64.spdx.json ]; then
-        echo "Head image lacks SBOM attestation; generating with Trivy..."
-        trivy image --format spdx-json --output sboms/head/sbom-amd64.spdx.json "${{ inputs.head-image }}" || true
-        cleanup_file sboms/head/sbom-amd64.spdx.json
+      echo "Configured platforms: ${PLATFORMS[*]:-(single platform fallback)}"
+
+      for platform in "${PLATFORMS[@]}"; do
+        arch_tag=$(echo "$platform" | sed -e 's#^[a-zA-Z0-9_-]*/##' -e 's#/#-#g')
+
+        # Head image extraction & fallback
+        if [ "$use_inbuild" = "true" ]; then
+          echo "Attempting extraction of built-in SBOM for head image ($platform)..."
+          docker buildx imagetools inspect "${{ inputs.head-image }}" \
+            --format "{{ json (index .SBOM \"${platform}\").SPDX }}" > "sboms/head/sbom-${arch_tag}.spdx.json" 2>/dev/null || true
+          cleanup_file "sboms/head/sbom-${arch_tag}.spdx.json"
+        fi
+
+        if [ ! -f "sboms/head/sbom-${arch_tag}.spdx.json" ]; then
+          echo "Generating SBOM for head image ($platform) with Trivy..."
+          if ! trivy image --skip-version-check --platform "$platform" --format spdx-json --output "sboms/head/sbom-${arch_tag}.spdx.json" "${{ inputs.head-image }}"; then
+            echo "::warning::Trivy image scan failed for head image ($platform)"
+          fi
+          cleanup_file "sboms/head/sbom-${arch_tag}.spdx.json"
+        fi
+
+        # Target image extraction & fallback
+        if [ "$use_inbuild" = "true" ]; then
+          echo "Attempting extraction of built-in SBOM for target image ($platform)..."
+          docker buildx imagetools inspect "${{ inputs.target-image }}" \
+            --format "{{ json (index .SBOM \"${platform}\").SPDX }}" > "sboms/target/sbom-${arch_tag}.spdx.json" 2>/dev/null || true
+          cleanup_file "sboms/target/sbom-${arch_tag}.spdx.json"
+        fi
+
+        if [ ! -f "sboms/target/sbom-${arch_tag}.spdx.json" ]; then
+          echo "Generating SBOM for target image ($platform) with Trivy..."
+          if ! trivy image --skip-version-check --platform "$platform" --format spdx-json --output "sboms/target/sbom-${arch_tag}.spdx.json" "${{ inputs.target-image }}"; then
+            echo "::warning::Trivy image scan failed for target image ($platform)"
+          fi
+          cleanup_file "sboms/target/sbom-${arch_tag}.spdx.json"
+        fi
+      done
+
+      # Fallbacks if no platform-specific SBOMs were extracted (e.g. single-arch image without index)
+      if [ -z "$(find sboms/head -type f -name 'sbom-*.spdx.json' 2>/dev/null)" ]; then
+        if [ "$use_inbuild" = "true" ]; then
+          docker buildx imagetools inspect "${{ inputs.head-image }}" \
+            --format '{{ json .SBOM.SPDX }}' > sboms/head/sbom-default.spdx.json 2>/dev/null || true
+          cleanup_file sboms/head/sbom-default.spdx.json
+        fi
+
+        if [ ! -f sboms/head/sbom-default.spdx.json ]; then
+          echo "Generating default head SBOM directly with Trivy..."
+          if ! trivy image --skip-version-check --format spdx-json --output sboms/head/sbom-default.spdx.json "${{ inputs.head-image }}"; then
+            head_sbom_err="Failed to generate SBOM with Trivy for head image"
+          fi
+          cleanup_file sboms/head/sbom-default.spdx.json
+        fi
       fi
 
-      # Extract platform SBOMs for target image
-      echo "Extracting platform SBOMs for target image: ${{ inputs.target-image }}..."
-      docker buildx imagetools inspect "${{ inputs.target-image }}" \
-        --format '{{ json (index .SBOM "linux/amd64").SPDX }}' > sboms/target/sbom-amd64.spdx.json 2>/dev/null || true
-      cleanup_file sboms/target/sbom-amd64.spdx.json
+      if [ -z "$(find sboms/target -type f -name 'sbom-*.spdx.json' 2>/dev/null)" ]; then
+        if [ "$use_inbuild" = "true" ]; then
+          docker buildx imagetools inspect "${{ inputs.target-image }}" \
+            --format '{{ json .SBOM.SPDX }}' > sboms/target/sbom-default.spdx.json 2>/dev/null || true
+          cleanup_file sboms/target/sbom-default.spdx.json
+        fi
 
-      docker buildx imagetools inspect "${{ inputs.target-image }}" \
-        --format '{{ json (index .SBOM "linux/arm64").SPDX }}' > sboms/target/sbom-arm64.spdx.json 2>/dev/null || true
-      cleanup_file sboms/target/sbom-arm64.spdx.json
-
-      if [ ! -f sboms/target/sbom-amd64.spdx.json ] && [ ! -f sboms/target/sbom-arm64.spdx.json ]; then
-        docker buildx imagetools inspect "${{ inputs.target-image }}" \
-          --format '{{ json .SBOM.SPDX }}' > sboms/target/sbom-amd64.spdx.json 2>/dev/null || true
-        cleanup_file sboms/target/sbom-amd64.spdx.json
+        if [ ! -f sboms/target/sbom-default.spdx.json ]; then
+          echo "Generating default target SBOM directly with Trivy..."
+          if ! trivy image --skip-version-check --format spdx-json --output sboms/target/sbom-default.spdx.json "${{ inputs.target-image }}"; then
+            target_sbom_err="Failed to generate SBOM with Trivy for target image"
+          fi
+          cleanup_file sboms/target/sbom-default.spdx.json
+        fi
       fi
 
-      # Fallback to generating target SBOM with Trivy if attestation missing
-      if [ ! -f sboms/target/sbom-amd64.spdx.json ] && [ ! -f sboms/target/sbom-arm64.spdx.json ]; then
-        echo "Target image lacks SBOM attestation; attempting to generate with Trivy..."
-        trivy image --format spdx-json --output sboms/target/sbom-amd64.spdx.json "${{ inputs.target-image }}" || true
-        cleanup_file sboms/target/sbom-amd64.spdx.json
+      shopt -s nullglob
+      head_files=(sboms/head/sbom-*.spdx.json)
+      target_files=(sboms/target/sbom-*.spdx.json)
+
+      if [ ${#head_files[@]} -eq 0 ] && [ -z "$head_sbom_err" ]; then
+        head_sbom_err="No SBOM generated and head image could not be inspected"
+      fi
+
+      if [ ${#target_files[@]} -eq 0 ] && [ -z "$target_sbom_err" ]; then
+        target_sbom_err="No SBOM generated and target baseline image could not be inspected"
+      fi
+
+      # Diagnostic overview
+      echo ""
+      echo "================================================================================"
+      echo "                      SBOM EXTRACTION DIAGNOSTIC OVERVIEW                       "
+      echo "================================================================================"
+      if [ -n "$head_sbom_err" ]; then
+        echo "HEAD Image (${{ inputs.head-image }}): ❌ FAILED - $head_sbom_err"
+      else
+        echo "HEAD Image (${{ inputs.head-image }}): ✅ SUCCESS"
+        for f in "${head_files[@]}"; do
+          echo "  - $(basename "$f") ($(wc -c < "$f") bytes)"
+        done
+      fi
+
+      if [ -n "$target_sbom_err" ]; then
+        echo "TARGET Baseline Image (${{ inputs.target-image }}): ❌ FAILED - $target_sbom_err"
+      else
+        echo "TARGET Baseline Image (${{ inputs.target-image }}): ✅ SUCCESS"
+        for f in "${target_files[@]}"; do
+          echo "  - $(basename "$f") ($(wc -c < "$f") bytes)"
+        done
+      fi
+      echo "================================================================================"
+      echo ""
+
+      has_sbom_err=false
+      if [ -n "$head_sbom_err" ]; then
+        echo "::error::Head SBOM extraction failed: $head_sbom_err"
+        has_sbom_err=true
+      fi
+      if [ -n "$target_sbom_err" ]; then
+        echo "::error::Target baseline SBOM extraction failed: $target_sbom_err"
+        has_sbom_err=true
+      fi
+
+      if [ "$has_sbom_err" = "true" ]; then
+        echo "::error::Both head and target images must have valid SBOMs to proceed with differential scanning."
+        exit 1
       fi
 
       # Expose extracted head SBOMs to workspace root for workflow artifact uploads
-      [ -f sboms/head/sbom-amd64.spdx.json ] && cp sboms/head/sbom-amd64.spdx.json sbom-amd64.spdx.json || true
-      [ -f sboms/head/sbom-arm64.spdx.json ] && cp sboms/head/sbom-arm64.spdx.json sbom-arm64.spdx.json || true
+      for f in sboms/head/sbom-*.spdx.json; do
+        [ -f "$f" ] || continue
+        cp "$f" "$(basename "$f")" || true
+      done
 
   - name: Scan Multi-Platform SBOMs and Generate Delta
     shell: bash
     run: |
       export PATH="$HOME/.local/bin:$PATH"
+      export TRIVY_SKIP_VERSION_CHECK="true"
       mkdir -p cve-reports/head cve-reports/target
 
-      # Scan each available head SBOM
-      for f in sboms/head/sbom-*.spdx.json; do
-        [ -f "$f" ] || continue
-        arch=$(basename "$f" .spdx.json | sed 's/sbom-//')
-        echo "Scanning head SBOM for architecture: $arch"
-        trivy sbom --format json --output "cve-reports/head/cve-${arch}.json" "$f" || true
-      done
+      shopt -s nullglob
+      head_sboms=(sboms/head/sbom-*.spdx.json)
+      target_sboms=(sboms/target/sbom-*.spdx.json)
 
-      # Scan each available target SBOM
-      for f in sboms/target/sbom-*.spdx.json; do
-        [ -f "$f" ] || continue
-        arch=$(basename "$f" .spdx.json | sed 's/sbom-//')
-        echo "Scanning target SBOM for architecture: $arch"
-        trivy sbom --format json --output "cve-reports/target/cve-${arch}.json" "$f" || true
-      done
+      head_ok=true
+      target_ok=true
+      head_report_count=0
+      target_report_count=0
 
-      # Run multi-arch set-based diff
-      node "${{ github.action_path }}/cve-diff.js" \
-        "cve-reports/target" \
-        "cve-reports/head" \
-        "${{ inputs.target-branch }}" > "${{ inputs.output-delta }}" || true
+      head_summary=()
+      target_summary=()
 
-      # Generate full markdown summary report for primary platform
-      primary_sbom=""
-      if [ -f sboms/head/sbom-amd64.spdx.json ]; then
-        primary_sbom="sboms/head/sbom-amd64.spdx.json"
-      elif [ -f sboms/head/sbom-arm64.spdx.json ]; then
-        primary_sbom="sboms/head/sbom-arm64.spdx.json"
+      # 1. Scan Head SBOMs
+      if [ ${#head_sboms[@]} -eq 0 ]; then
+        head_ok=false
+        head_summary+=("  - ❌ No SBOM files found in sboms/head/")
+      else
+        for f in "${head_sboms[@]}"; do
+          arch=$(basename "$f" .spdx.json | sed 's/sbom-//')
+          out_json="cve-reports/head/cve-${arch}.json"
+          err_log="cve-reports/head/cve-${arch}.err"
+
+          echo "Scanning head SBOM for architecture: $arch"
+          if trivy sbom --skip-version-check --format json --output "$out_json" "$f" 2>"$err_log"; then
+            if [ -s "$out_json" ]; then
+              vuln_cnt=$(grep -o '"VulnerabilityID"' "$out_json" 2>/dev/null | wc -l || echo 0)
+              if [ "$vuln_cnt" -eq 0 ]; then
+                echo "::warning::Head image architecture '${arch}' has 0 CVE findings. Verify that OS/packages were recognized."
+                head_summary+=("  - ${arch}: ⚠️ WARNING (0 vulnerability findings detected)")
+              else
+                head_summary+=("  - ${arch}: ✅ OK (${vuln_cnt} vulnerability findings)")
+              fi
+              head_report_count=$((head_report_count + 1))
+            else
+              head_ok=false
+              head_summary+=("  - ${arch}: ❌ FAILED (Output report was empty / 0 bytes)")
+            fi
+          else
+            head_ok=false
+            err_msg=$(tail -n 2 "$err_log" | tr '\n' ' ' | sed 's/  */ /g')
+            [ -z "$err_msg" ] && err_msg="Trivy scan exited with non-zero status"
+            head_summary+=("  - ${arch}: ❌ FAILED (${err_msg})")
+          fi
+        done
       fi
 
-      if [ -n "$primary_sbom" ]; then
-        trivy sbom \
-          --format template \
-          --template "@${{ github.action_path }}/markdown.tpl" \
-          --output "${{ inputs.output-summary }}" \
-          "$primary_sbom" || true
+      # 2. Scan Target SBOMs
+      if [ ${#target_sboms[@]} -eq 0 ]; then
+        target_ok=false
+        target_summary+=("  - ❌ No SBOM files found in sboms/target/")
+      else
+        for f in "${target_sboms[@]}"; do
+          arch=$(basename "$f" .spdx.json | sed 's/sbom-//')
+          out_json="cve-reports/target/cve-${arch}.json"
+          err_log="cve-reports/target/cve-${arch}.err"
+
+          echo "Scanning target SBOM for architecture: $arch"
+          if trivy sbom --skip-version-check --format json --output "$out_json" "$f" 2>"$err_log"; then
+            if [ -s "$out_json" ]; then
+              vuln_cnt=$(grep -o '"VulnerabilityID"' "$out_json" 2>/dev/null | wc -l || echo 0)
+              if [ "$vuln_cnt" -eq 0 ]; then
+                echo "::warning::Target baseline image architecture '${arch}' has 0 CVE findings. Verify that OS/packages were recognized."
+                target_summary+=("  - ${arch}: ⚠️ WARNING (0 vulnerability findings detected)")
+              else
+                target_summary+=("  - ${arch}: ✅ OK (${vuln_cnt} vulnerability findings)")
+              fi
+              target_report_count=$((target_report_count + 1))
+            else
+              target_ok=false
+              target_summary+=("  - ${arch}: ❌ FAILED (Output report was empty / 0 bytes)")
+            fi
+          else
+            target_ok=false
+            err_msg=$(tail -n 2 "$err_log" | tr '\n' ' ' | sed 's/  */ /g')
+            [ -z "$err_msg" ] && err_msg="Trivy scan exited with non-zero status"
+            target_summary+=("  - ${arch}: ❌ FAILED (${err_msg})")
+          fi
+        done
+      fi
+
+      # 3. Print Comprehensive Diagnostic Overview
+      echo ""
+      echo "================================================================================"
+      echo "                   CVE VULNERABILITY SCAN DIAGNOSTIC OVERVIEW                  "
+      echo "================================================================================"
+      echo "HEAD Image: ${{ inputs.head-image }}"
+      for line in "${head_summary[@]}"; do
+        echo "$line"
+      done
+      echo ""
+      echo "TARGET Baseline Image: ${{ inputs.target-image }} (branch: '${{ inputs.target-branch }}')"
+      for line in "${target_summary[@]}"; do
+        echo "$line"
+      done
+      echo "================================================================================"
+      echo ""
+
+      # 4. Enforce Gating: Both must have succeeded with valid reports
+      has_error=false
+      if [ "$head_ok" != "true" ] || [ "$head_report_count" -eq 0 ]; then
+        echo "::error::Head image CVE analysis failed or produced no reports."
+        has_error=true
+      fi
+
+      if [ "$target_ok" != "true" ] || [ "$target_report_count" -eq 0 ]; then
+        echo "::error::Target baseline CVE analysis failed or produced no reports."
+        has_error=true
+      fi
+
+      if [ "$has_error" = "true" ]; then
+        echo "::error::Aborting differential analysis: both head and target scans must succeed before diffing."
+        exit 1
+      fi
+
+      # 5. Run multi-arch set-based diff and generate consolidated full summary report
+      echo "Both head and target scans succeeded. Computing set-based vulnerability delta..."
+      if ! node "${{ github.action_path }}/cve-diff.js" \
+        "cve-reports/target" \
+        "cve-reports/head" \
+        "${{ inputs.target-branch }}" \
+        "${{ inputs.output-summary }}" > "${{ inputs.output-delta }}"; then
+        echo "::error::Failed to generate CVE differential report"
+        exit 1
       fi
 
   - name: Publish Reports to Step Summary

cve-diff.js

@@ -24,6 +24,7 @@ const SEVERITY_BADGES = {
  */
 function loadReportsForArg(arg) {
   const cves = new Map();
+  const scannedArchs = new Set();
   const filePaths = [];
 
   for (const part of arg.split(',').map((s) => s.trim())) {
@@ -41,35 +42,55 @@ function loadReportsForArg(arg) {
     }
   }
 
+  if (filePaths.length === 0) {
+    console.error(`::error::No CVE JSON report files found for path: ${arg}`);
+    process.exit(1);
+  }
+
+  let loadedFiles = 0;
   for (const filePath of filePaths) {
     let stat;
     try {
       stat = fs.statSync(filePath);
-    } catch {
-      continue;
+    } catch (e) {
+      console.error(`::error::Failed to access report file ${filePath}: ${e.message}`);
+      process.exit(1);
+    }
+    if (stat.size === 0) {
+      console.error(`::error::CVE report file is empty (0 bytes): ${filePath}`);
+      process.exit(1);
     }
-    if (stat.size === 0) continue;
 
-    const baseName = path.basename(filePath).toLowerCase();
+    const baseName = path.basename(filePath, '.json').toLowerCase();
     let arch = 'all';
-    if (baseName.includes('amd64')) {
+    const cveMatch = baseName.match(/^cve-([a-z0-9_.-]+)$/i);
+    if (cveMatch) {
+      arch = cveMatch[1];
+    } else if (baseName.includes('amd64')) {
       arch = 'amd64';
     } else if (baseName.includes('arm64') || baseName.includes('aarch64')) {
       arch = 'arm64';
     }
+    if (arch !== 'all') {
+      scannedArchs.add(arch);
+    }
 
     let data;
     try {
       const content = fs.readFileSync(filePath, 'utf8');
       data = JSON.parse(content);
-    } catch {
-      continue;
+    } catch (e) {
+      console.error(`::error::Invalid JSON in CVE report file ${filePath}: ${e.message}`);
+      process.exit(1);
     }
 
     if (!data || typeof data !== 'object' || !Array.isArray(data.Results)) {
-      continue;
+      console.error(`::error::Malformed Trivy report structure (missing Results array) in: ${filePath}`);
+      process.exit(1);
     }
 
+    loadedFiles++;
+
     for (const result of data.Results) {
       const target = result.Target || result.Type || 'App';
       const vulns = Array.isArray(result.Vulnerabilities) ? result.Vulnerabilities : [];
@@ -88,15 +109,23 @@ function loadReportsForArg(arg) {
     }
   }
 
+  if (loadedFiles === 0) {
+    console.error(`::error::No valid CVE reports could be loaded for path: ${arg}`);
+    process.exit(1);
+  }
+
+  cves.scannedArchs = scannedArchs;
   return cves;
 }
 
 /**
  * Formats a vulnerability record into a Markdown table row.
  * @param {object} v
+ * @param {Set<string>} [allScannedArchs]
+ * @param {boolean} [showArch]
  * @returns {string}
  */
-function formatVulnRow(v) {
+function formatVulnRow(v, allScannedArchs = new Set(), showArch = true) {
   const sev = v.Severity || 'UNKNOWN';
   const badge = SEVERITY_BADGES[sev] || `⚪ ${sev}`;
   const vid = v.VulnerabilityID || '';
@@ -104,14 +133,6 @@ function formatVulnRow(v) {
   const link = url ? `[${vid}](${url})` : vid;
   const pkg = v.PkgName || '';
 
-  const archs = v._archs || new Set(['all']);
-  let archBadge;
-  if ((archs.has('amd64') && archs.has('arm64')) || archs.has('all')) {
-    archBadge = '`all`';
-  } else {
-    archBadge = `\`${Array.from(archs).sort().join(', ')}\``;
-  }
-
   const installed = v.InstalledVersion || '-';
   const fixed = v.FixedVersion || '-';
   let title = (v.Title || v.Description || '').replace(/\n/g, ' ').trim();
@@ -119,7 +140,22 @@ function formatVulnRow(v) {
     title = title.slice(0, 77) + '...';
   }
 
-  return `| ${badge} | ${link} | \`${pkg}\` | ${archBadge} | ${installed} | ${fixed} | ${title} |`;
+  if (showArch) {
+    const archs = v._archs || new Set(['all']);
+    let archBadge;
+    if (
+      archs.has('all') ||
+      (allScannedArchs && allScannedArchs.size > 1 && archs.size === allScannedArchs.size) ||
+      (archs.has('amd64') && archs.has('arm64'))
+    ) {
+      archBadge = '`all`';
+    } else {
+      archBadge = `\`${Array.from(archs).sort().join(', ')}\``;
+    }
+    return `| ${badge} | ${link} | \`${pkg}\` | ${archBadge} | ${installed} | ${fixed} | ${title} |`;
+  }
+
+  return `| ${badge} | ${link} | \`${pkg}\` | ${installed} | ${fixed} | ${title} |`;
 }
 
 /**
@@ -130,19 +166,17 @@ function formatVulnRow(v) {
  * @returns {string}
  */
 function renderMarkdownDiff(baseCves, branchCves, baseName = 'main') {
-  if (baseCves.size === 0) {
-    return [
-      `### 🔄 Vulnerability Delta (vs \`${baseName}\`)`,
-      '',
-      '> [!NOTE]',
-      `> No baseline scan from \`${baseName}\` was available to compare against.`,
-      '',
-    ].join('\n');
-  }
-
   const baseKeys = new Set(baseCves.keys());
   const branchKeys = new Set(branchCves.keys());
 
+  if (branchCves.size === 0) {
+    console.error('::warning::Head image contains 0 reported vulnerabilities. Verify that packages and dependencies were recognized.');
+  }
+
+  if (baseCves.size === 0) {
+    console.error(`::warning::Baseline target (${baseName}) contains 0 reported vulnerabilities.`);
+  }
+
   const newKeys = [];
   let unchangedCount = 0;
   for (const key of branchKeys) {
@@ -171,26 +205,52 @@ function renderMarkdownDiff(baseCves, branchCves, baseName = 'main') {
     return aPkg.localeCompare(bPkg);
   }
 
+  const allScannedArchs = new Set([
+    ...(baseCves.scannedArchs || []),
+    ...(branchCves.scannedArchs || []),
+  ]);
+  const showArch = allScannedArchs.size > 1;
+
   const newVulns = newKeys.map((k) => branchCves.get(k)).sort(sortVulns);
   const resolvedVulns = resolvedKeys.map((k) => baseCves.get(k)).sort(sortVulns);
 
   const lines = [
     `### 🔄 Vulnerability Delta (vs \`${baseName}\`)`,
     '',
-    '| Metric | Count |',
-    '| :--- | :--- |',
-    `| 🚨 **New Vulnerabilities** | ${newVulns.length > 0 ? `🚨 **${newVulns.length}**` : '0'} |`,
-    `| ✅ **Resolved Vulnerabilities** | ${resolvedVulns.length > 0 ? `✅ **${resolvedVulns.length}**` : '0'} |`,
-    `| ⚪ **Unchanged Vulnerabilities** | ${unchangedCount} |`,
-    '',
-    `#### 🚨 New Vulnerabilities Introduced (${newVulns.length})`,
   ];
 
+  if (branchCves.size === 0 && baseCves.size === 0) {
+    lines.push('> [!WARNING]');
+    lines.push('> Both the head image and baseline target have **0 reported vulnerabilities**.');
+    lines.push('');
+  } else if (branchCves.size === 0) {
+    lines.push('> [!WARNING]');
+    lines.push('> The head image has **0 reported vulnerabilities**. Verify that OS packages and language dependencies were properly indexed in the SBOM.');
+    lines.push('');
+  } else if (baseCves.size === 0) {
+    lines.push('> [!WARNING]');
+    lines.push(`> The baseline image (\`${baseName}\`) has **0 reported vulnerabilities**.`);
+    lines.push('');
+  }
+
+  lines.push('| Metric | Count |');
+  lines.push('| :--- | :--- |');
+  lines.push(`| 🚨 **New Vulnerabilities** | ${newVulns.length > 0 ? `🚨 **${newVulns.length}**` : '0'} |`);
+  lines.push(`| ✅ **Resolved Vulnerabilities** | ${resolvedVulns.length > 0 ? `✅ **${resolvedVulns.length}**` : '0'} |`);
+  lines.push(`| ⚪ **Unchanged Vulnerabilities** | ${unchangedCount} |`);
+  lines.push('');
+  lines.push(`#### 🚨 New Vulnerabilities Introduced (${newVulns.length})`);
+
   if (newVulns.length > 0) {
-    lines.push('| Severity | CVE | Package | Arch | Installed | Fixed In | Title |');
-    lines.push('| :--- | :--- | :--- | :--- | :--- | :--- | :--- |');
+    if (showArch) {
+      lines.push('| Severity | CVE | Package | Arch | Installed | Fixed In | Title |');
+      lines.push('| :--- | :--- | :--- | :--- | :--- | :--- | :--- |');
+    } else {
+      lines.push('| Severity | CVE | Package | Installed | Fixed In | Title |');
+      lines.push('| :--- | :--- | :--- | :--- | :--- | :--- |');
+    }
     for (const v of newVulns) {
-      lines.push(formatVulnRow(v));
+      lines.push(formatVulnRow(v, allScannedArchs, showArch));
     }
   } else {
     lines.push('✅ No new vulnerabilities introduced in this build.');
@@ -199,10 +259,15 @@ function renderMarkdownDiff(baseCves, branchCves, baseName = 'main') {
 
   lines.push(`#### ✅ Resolved / Removed Vulnerabilities (${resolvedVulns.length})`);
   if (resolvedVulns.length > 0) {
-    lines.push('| Severity | CVE | Package | Arch | Previously Installed | Fixed In | Title |');
-    lines.push('| :--- | :--- | :--- | :--- | :--- | :--- | :--- |');
+    if (showArch) {
+      lines.push('| Severity | CVE | Package | Arch | Previously Installed | Fixed In | Title |');
+      lines.push('| :--- | :--- | :--- | :--- | :--- | :--- | :--- |');
+    } else {
+      lines.push('| Severity | CVE | Package | Previously Installed | Fixed In | Title |');
+      lines.push('| :--- | :--- | :--- | :--- | :--- | :--- |');
+    }
     for (const v of resolvedVulns) {
-      lines.push(formatVulnRow(v));
+      lines.push(formatVulnRow(v, allScannedArchs, showArch));
     }
   } else {
     lines.push('⚪ No existing vulnerabilities were resolved.');
@@ -212,22 +277,82 @@ function renderMarkdownDiff(baseCves, branchCves, baseName = 'main') {
   return lines.join('\n');
 }
 
+/**
+ * Renders a full markdown summary report of all vulnerabilities in a scan.
+ * @param {Map<string, object>} cves
+ * @returns {string}
+ */
+function renderFullSummary(cves) {
+  const allScannedArchs = cves.scannedArchs || new Set();
+  const showArch = allScannedArchs.size > 1;
+
+  const lines = [
+    '### 🛡️ Security Scan Report',
+    '',
+  ];
+
+  if (cves.size === 0) {
+    lines.push('✅ No vulnerabilities found.');
+    lines.push('');
+    return lines.join('\n');
+  }
+
+  function sortVulns(a, b) {
+    const aSev = a.Severity || 'UNKNOWN';
+    const bSev = b.Severity || 'UNKNOWN';
+    const aIdx = SEVERITY_ORDER.indexOf(aSev) !== -1 ? SEVERITY_ORDER.indexOf(aSev) : 99;
+    const bIdx = SEVERITY_ORDER.indexOf(bSev) !== -1 ? SEVERITY_ORDER.indexOf(bSev) : 99;
+    if (aIdx !== bIdx) return aIdx - bIdx;
+    const aPkg = a.PkgName || '';
+    const bPkg = b.PkgName || '';
+    return aPkg.localeCompare(bPkg);
+  }
+
+  const sortedVulns = Array.from(cves.values()).sort(sortVulns);
+
+  lines.push(`| Metric | Count |`);
+  lines.push(`| :--- | :--- |`);
+  lines.push(`| Total Vulnerabilities | **${sortedVulns.length}** |`);
+  lines.push('');
+
+  if (showArch) {
+    lines.push('| Severity | CVE | Package | Arch | Installed | Fixed In | Title |');
+    lines.push('| :--- | :--- | :--- | :--- | :--- | :--- | :--- |');
+  } else {
+    lines.push('| Severity | CVE | Package | Installed | Fixed In | Title |');
+    lines.push('| :--- | :--- | :--- | :--- | :--- | :--- |');
+  }
+
+  for (const v of sortedVulns) {
+    lines.push(formatVulnRow(v, allScannedArchs, showArch));
+  }
+  lines.push('');
+
+  return lines.join('\n');
+}
+
 function main() {
   const args = process.argv.slice(2);
   if (args.length < 2) {
-    console.error('Usage: cve-diff.js <base_report(s)> <branch_report(s)> [base_name]');
+    console.error('Usage: cve-diff.js <base_report(s)> <branch_report(s)> [base_name] [summary_output_path]');
     process.exit(1);
   }
 
   const baseArg = args[0];
   const branchArg = args[1];
   const baseName = args[2] || 'main';
+  const summaryOutputPath = args[3];
 
   const baseCves = loadReportsForArg(baseArg);
   const branchCves = loadReportsForArg(branchArg);
 
   const output = renderMarkdownDiff(baseCves, branchCves, baseName);
   console.log(output);
+
+  if (summaryOutputPath) {
+    const summaryOutput = renderFullSummary(branchCves);
+    fs.writeFileSync(summaryOutputPath, summaryOutput, 'utf8');
+  }
 }
 
 if (require.main === module) {
@@ -238,4 +363,5 @@ module.exports = {
   loadReportsForArg,
   formatVulnRow,
   renderMarkdownDiff,
+  renderFullSummary,
 };