Docker Security Scanning: Build Secure Container Images

Understanding Docker Security Scanning for Containers

In this comprehensive tutorial, you’ll discover how to implement security scanning in your Docker workflow to identify vulnerabilities before they reach production. By the end, you’ll have a robust security scanning pipeline that protects your applications and satisfies compliance requirements.

Container security isn’t just about the latest CVE headlines – it’s about building a culture of security-first thinking in your development workflow. During my work with the Docker community, I’ve seen too many teams discover critical vulnerabilities only after deployment.

The statistics are sobering: over 80% of container images in production contain at least one high-severity vulnerability. But here’s the good news – most of these are preventable with the right scanning approach.

Think of container security like airport security – you have multiple checkpoints, each catching different types of issues:

1. Base image scanning – Like checking your passport
2. Dependency scanning – Like checking your luggage
3. Configuration scanning – Like the metal detector
4. Runtime scanning – Like ongoing monitoring

Each layer is crucial, but today we’ll focus on building this into your development workflow.

Docker Scout is built into Docker Desktop and provides vulnerability scanning out of the box:

# Enable Docker Scout (if not already enabled)
docker scout version

# Scan an existing image
docker scout cves nginx:latest

# Quick vulnerability overview
docker scout quickview nginx:latest

Integrate scanning directly into your Dockerfile workflow:

# Multi-stage build with security scanning
FROM node:18-alpine AS base
WORKDIR /app

# Install dependencies first (better caching)
COPY package*.json ./
RUN npm ci --only=production

# Copy application code
COPY . .

# Build stage
FROM base AS builder
RUN npm run build

# Security scanning stage
FROM base AS security-scan
RUN npm audit --audit-level=high
# Note: This will fail the build if high-severity issues found

# Production stage
FROM node:18-alpine AS production
WORKDIR /app

# Copy only production files
COPY --from=builder /app/dist ./dist
COPY --from=base /app/node_modules ./node_modules
COPY --from=base /app/package.json ./

# Security: Non-root user
RUN addgroup -g 1001 -S nodejs && adduser -S appuser -u 1001
USER appuser

EXPOSE 3000
CMD ["npm", "start"]

Here’s how to integrate scanning into GitHub Actions:

name: Secure Docker Build

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

jobs:
  security-scan:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    
    - name: Build Docker image
      run: docker build -t myapp:latest .
    
    - name: Run Docker Scout scan
      run: |
        docker scout cves myapp:latest --format sarif --output scout-report.sarif
    
    - name: Upload scan results
      uses: github/codeql-action/upload-sarif@v2
      with:
        sarif_file: scout-report.sarif
    
    - name: Fail on critical vulnerabilities
      run: |
        docker scout cves myapp:latest --only-severity critical --exit-code

Let me share how we implemented this for a community project with 50+ microservices. We created a comprehensive scanning pipeline that reduced our security incidents by 90%.

1. Establish severity thresholds: Critical = block deployment, High = require approval
2. Regular base image updates: Update base images monthly minimum
3. Dependency management: Use tools like Dependabot for automatic updates
4. False positive handling: Maintain allowlists for unavoidable issues

For Kubernetes deployments, we recommend using admission controllers to enforce security policies at the cluster level.

After mastering vulnerability scanning, explore:

1. Runtime security monitoring with tools like Falco
2. Supply chain security with SLSA frameworks
3. Zero-trust networking for container communications
4. Compliance automation for SOC2, PCI-DSS requirements

• Share your security scanning setups in our Collabnix Slack
• Explore scout related resources 

Remember: security isn’t a destination, it’s a journey. Start with basic vulnerability scanning, then gradually build more sophisticated security practices into your workflow.

What security challenges are you facing in your container deployments? Join our community discussion and let’s solve them together!

Building secure containers isn’t just about avoiding vulnerabilities – it’s about creating a culture where security is everyone’s responsibility, not just the security team’s. Every scan you run makes your applications more resilient.