Container Security Checklist

A comprehensive security checklist for Dockerfiles and container images.

Build-Time Security

Base Image Security

• Use official or verified base images
• Pin base image to specific tag (not :latest)
• Consider digest pinning for critical applications
• Prefer minimal base images (Alpine, distroless, scratch)
• Scan base images for known vulnerabilities
• Keep base images updated regularly

Secrets Management

• Never hardcode secrets in Dockerfile
• Don't use ENV or ARG for sensitive data
• Use Docker build secrets (--secret flag)
• Use runtime configuration for secrets
• Scan for accidentally committed secrets
• Use .dockerignore to exclude secret files

Package Management

• Pin package versions for reproducibility
• Only install necessary packages (--no-install-recommends)
• Clean package manager cache in same layer
• Verify package signatures when possible
• Use official package repositories
• Audit dependencies for known vulnerabilities

User and Permissions

• Create and use non-root user
• Set USER directive before CMD/ENTRYPOINT
• Use high UID (>10000) for better isolation
• Set proper file ownership with COPY --chown
• Don't use sudo in containers
• Avoid privileged operations

Layer and File Security

• Use .dockerignore to exclude sensitive files
• Don't copy unnecessary files (use specific COPY)
• Remove secrets after use in same layer
• Don't log sensitive information
• Minimize number of layers
• Use multi-stage builds to exclude build secrets

Common Vulnerabilities

SSH/Remote Access

• Don't install or expose SSH (port 22)
• Don't install telnet, FTP, or other insecure protocols
• Use docker exec for debugging instead of SSH
• Don't run sshd in containers

Network Exposure

• Only EXPOSE necessary ports
• Don't bind to 0.0.0.0 in development images
• Use internal networks for inter-container communication
• Implement proper firewall rules
• Use TLS for network communications

File System Security

• Consider read-only root filesystem
• Use tmpfs for temporary files
• Set proper file permissions
• Don't store secrets in environment variables
• Use volume mounts for sensitive data

Runtime Security

Container Configuration

• Run with --read-only flag when possible
• Drop unnecessary capabilities (--cap-drop)
• Use security profiles (AppArmor, SELinux)
• Set resource limits (CPU, memory)
• Use user namespaces
• Enable content trust (DOCKER_CONTENT_TRUST)

Health and Monitoring

• Implement HEALTHCHECK in Dockerfile
• Monitor container logs
• Set up security scanning in CI/CD
• Use runtime security tools
• Monitor for anomalous behavior
• Implement proper logging without secrets

Network Security

• Use custom bridge networks
• Implement network segmentation
• Use encrypted overlays for swarm
• Configure DNS properly
• Use service mesh for microservices
• Implement network policies

Image Registry Security

Registry Configuration

• Use private registries for internal images
• Enable image scanning in registry
• Implement access controls
• Use image signing (Docker Content Trust)
• Scan for vulnerabilities before pull
• Regularly update registry software

Image Distribution

• Sign images before distribution
• Verify image signatures on pull
• Use TLS for registry communication
• Implement role-based access control
• Audit image pull/push events
• Use image provenance metadata

Security Scanning Tools

Static Analysis

• hadolint - Dockerfile linting
• Checkov - Policy-as-code scanning
• dockerfilelint - Best practices checker

Vulnerability Scanning

• Trivy - Comprehensive vulnerability scanner
• Snyk - Dependency vulnerability scanner
• Clair - Container vulnerability analysis
• Anchore - Deep image inspection

Runtime Security

• Falco - Runtime threat detection
• Aqua Security - Container security platform
• Sysdig - Container monitoring and security

Compliance and Standards

Industry Standards

• Follow CIS Docker Benchmark
• Comply with NIST guidelines
• Adhere to OWASP Container Security
• Meet PCI DSS requirements (if applicable)
• Follow SOC 2 controls (if applicable)

Security Policies

• Document security requirements
• Implement security review process
• Define incident response procedures
• Regular security audits
• Security training for developers
• Maintain security documentation

Quick Security Wins

Easy Fixes

1. Use specific base image tags

   FROM alpine:3.21  # Not alpine:latest

2. Run as non-root

   USER appuser

3. Clean package cache

   RUN apk add --no-cache package

4. Don't expose unnecessary ports

   # Only expose what's needed
   EXPOSE 8080

5. Add health checks

   HEALTHCHECK CMD curl -f http://localhost/ || exit 1

Security Checklist Summary

Resources

• CIS Docker Benchmark
• OWASP Docker Security
• NIST Container Security Guide
• Docker Security Best Practices