Microsoft Application Inspector

When to Use Application Inspector

Ideal scenarios:

• Technology stack profiling and discovery
• Identifying security-relevant code patterns (authentication, cryptography, logging)
• Pre-audit reconnaissance to understand codebase capabilities
• Detecting use of sensitive APIs and security controls
• Creating software composition reports
• Finding data handling patterns (PII, credentials, encryption)

Complements other tools:

• Use before Semgrep/CodeQL for context on what security patterns exist
• Combine with SARIF Issue Reporter for detailed findings analysis
• Use alongside SCA tools to understand both dependencies and implementation

When NOT to Use

Do NOT use this skill for:

• Finding specific vulnerabilities (use Semgrep, CodeQL, or SAST tools)
• Dependency vulnerability scanning (use OSV-Scanner or Depscan)
• Secrets detection (use Gitleaks)
• IaC security analysis (use KICS)
• Deep data flow analysis

Installation

# .NET tool (recommended)
dotnet tool install --global Microsoft.CST.ApplicationInspector.CLI

# Update
dotnet tool update --global Microsoft.CST.ApplicationInspector.CLI

# Verify
appinspector --version

# Docker
docker pull mcr.microsoft.com/app-inspector
docker run -v ${PWD}:/app mcr.microsoft.com/app-inspector analyze -s /app -f sarif -o /app/results.sarif

Core Workflow

1. Quick Analysis

# Analyze directory with default rules
appinspector analyze -s /path/to/code -f html -o report.html

# Text summary
appinspector analyze -s /path/to/code -f text

# JSON output
appinspector analyze -s /path/to/code -f json -o results.json

2. SARIF Output

# Generate SARIF report
appinspector analyze -s /path/to/code \
  --output-file-format sarif \
  --output-file-path results.sarif

# With custom rules
appinspector analyze -s /path/to/code \
  -r /path/to/custom-rules \
  --output-file-format sarif \
  --output-file-path results.sarif

# Single-threaded for stability
appinspector analyze -s /path/to/code \
  --single-threaded \
  --file-timeout 500000 \
  --output-file-format sarif \
  --output-file-path results.sarif

3. Security-Focused Analysis

# Focus on security features
appinspector analyze -s /path/to/code \
  -t "Authentication,Cryptography,Authorization" \
  -f json -o security-features.json

# Exclude test files
appinspector analyze -s /path/to/code \
  -e "test,tests,spec,__pycache__" \
  -f sarif -o results.sarif

Understanding Output

Tag Categories

Application Inspector detects patterns across categories:

Severity Levels

• Critical: High-risk patterns (hardcoded secrets, weak crypto)
• Important: Security-relevant code requiring review
• Moderate: Potentially sensitive functionality
• ManualReview: Patterns requiring human analysis
• BestPractice: Recommended patterns found

Custom Rules

Rule Structure

{
  "name": "Detect hardcoded API keys",
  "id": "DS123456",
  "description": "Identifies potential hardcoded API keys",
  "tags": [
    "Data.Credentials.APIKey"
  ],
  "severity": "Critical",
  "patterns": [
    {
      "pattern": "api[_-]?key\\s*=\\s*['\"][a-zA-Z0-9]{20,}['\"]",
      "type": "regex",
      "confidence": "High",
      "scopes": [
        "code"
      ]
    }
  ]
}

Rule File Format

Create custom-rules.json:

[
  {
    "name": "AWS Access Key",
    "id": "DS001",
    "tags": ["Data.Credentials.AWS"],
    "severity": "Critical",
    "patterns": [
      {
        "pattern": "AKIA[0-9A-Z]{16}",
        "type": "regex",
        "confidence": "High"
      }
    ]
  }
]

Use with:

appinspector analyze -s /code -r custom-rules.json -f sarif -o results.sarif

Verification Commands

# Verify rules
appinspector verify-rules -r /path/to/rules

# Test specific rule
appinspector verify-rules -r custom-rules.json

# List default rules
appinspector exportrules -o default-rules.json

CI/CD Integration (GitHub Actions)

name: Application Inspector

on:
  push:
    branches: [main]
  pull_request:
  schedule:
    - cron: '0 0 1 * *'

jobs:
  analyze:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v4

      - name: Setup .NET
        uses: actions/setup-dotnet@v4
        with:
          dotnet-version: '8.0'

      - name: Install Application Inspector
        run: dotnet tool install --global Microsoft.CST.ApplicationInspector.CLI

      - name: Run Analysis
        run: |
          appinspector analyze \
            -s ${{ github.workspace }} \
            --output-file-format sarif \
            --output-file-path results.sarif \
            --single-threaded \
            --disable-archive-crawling

      - name: Upload SARIF
        uses: github/codeql-action/upload-sarif@v3
        with:
          sarif_file: results.sarif
          category: application-inspector

      - name: Upload Results
        uses: actions/upload-artifact@v4
        if: always()
        with:
          name: application-inspector-results
          path: results.sarif

Configuration

Performance Options

# Single-threaded (more stable)
appinspector analyze -s /code --single-threaded

# Increase timeout for large files
appinspector analyze -s /code --file-timeout 500000

# Disable archive scanning (faster)
appinspector analyze -s /code --disable-archive-crawling

# Process only specific languages
appinspector analyze -s /code -l "javascript,typescript,python"

Exclusions

# Exclude paths
appinspector analyze -s /code \
  -e "node_modules,vendor,dist,build,__pycache__"

# Exclude file patterns
appinspector analyze -s /code \
  -e "*.min.js,*.test.js,*.spec.ts"

Common Use Cases

1. Pre-Audit Technology Discovery

# Generate comprehensive technology report
appinspector analyze -s /code -f html -o tech-report.html

# Review report to understand:
# - What frameworks are used
# - What crypto libraries are present
# - How authentication is implemented
# - What cloud services are integrated

2. Security Feature Inventory

# Find all security-relevant patterns
appinspector analyze -s /code \
  -t "Authentication,Authorization,Cryptography,Data.Credentials" \
  -f json -o security-inventory.json

3. Compliance Scanning

# Detect PII handling
appinspector analyze -s /code \
  -t "Data.PII" \
  -f sarif -o pii-report.sarif

# Find credential usage
appinspector analyze -s /code \
  -t "Data.Credentials" \
  -f sarif -o credentials-report.sarif

Interpreting Results

SARIF Structure

Application Inspector SARIF includes:

• Rules: Each detected pattern/tag
• Results: Specific code locations matching patterns
• Properties: Confidence, severity, tags
• Locations: File path, line number, code snippet

Filter by Severity

# Use SARIF tools to filter
pip install sarif-tools

# Extract critical findings only
sarif summary results.sarif --level error

# Filter by tag
sarif filter --level error --rule-id "DS.*Credentials.*" results.sarif

Limitations

• Not a vulnerability scanner: Identifies patterns, not exploits
• False positives: Regex-based detection can flag legitimate code
• Performance: Large codebases may require single-threaded mode
• Language coverage: Better for common languages (JS, Python, C#, Java)
• No data flow: Can't track how data moves through application

Rationalizations to Reject

References

• Repository: https://github.com/microsoft/ApplicationInspector
• Documentation: https://github.com/microsoft/ApplicationInspector/wiki
• Default Rules: https://github.com/microsoft/ApplicationInspector/tree/main/AppInspector/rules
• SARIF Spec: https://docs.oasis-open.org/sarif/sarif/v2.1.0/sarif-v2.1.0.html