Container Image Hardening Guide

What This Best Practice Entails and Why It Matters

Container images are the building blocks of modern application deployment. However, they can also be a significant security risk if not properly hardened. This best practice focuses on creating minimal, non-root, signed container images that include Software Bill of Materials (SBOMs).

Hardening your container images helps to:

• Reduce Attack Surface: By minimizing the components in a container, you limit the potential vulnerabilities.
• Enhance Security: Non-root images minimize the risk of privilege escalation attacks.
• Improve Compliance: Signed images provide traceability and accountability for software components.

Step-by-Step Implementation Guidance

1. Start with a Minimal Base Image: Use a lightweight image like Alpine or Distroless to reduce the number of packages.

   • Example: Instead of FROM ubuntu:latest, use FROM alpine:latest.

2. Run as a Non-Root User: Specify a non-root user in your Dockerfile.

   RUN addgroup -S myuser && adduser -S myuser -G myuser
   USER myuser
   

3. Limit Installed Packages: Only install the packages essential for your application. Use multi-stage builds to copy only required artifacts.

   • Example:

   FROM golang:alpine AS builder
   WORKDIR /app
   COPY . .
   RUN go build -o myapp
   
   FROM alpine:latest
   COPY --from=builder /app/myapp /usr/local/bin/myapp
   

4. Use Image Signing: Implement image signing to verify the integrity of your images. Tools like Docker Content Trust can be used.

   • Enable Docker Content Trust: export DOCKER_CONTENT_TRUST=1

5. Generate an SBOM: Use tools like Syft or CycloneDX to generate a Software Bill of Materials for your container images. This provides an inventory of components and can help in compliance audits.

   • Example: syft myimage:latest -o json > sbom.json

6. Regularly Update Images: Keep your base images and dependencies up to date to mitigate known vulnerabilities.

Common Mistakes Teams Make When Ignoring This Practice

• Using Default Root User: Running containers as root can lead to privilege escalation and other security risks.
• Overly Complex Images: Including extraneous packages and dependencies increases vulnerabilities.
• Neglecting Updates: Failing to regularly update images can result in exposure to known security issues.
• Ignoring SBOMs: Not generating SBOMs can lead to a lack of visibility into components, complicating compliance and security audits.

Tools and Techniques That Support This Practice

• Docker: The primary tool used for containerization.
• Syft: A tool for generating SBOMs from container images.
• Docker Content Trust: Enables image signing for verification.
• Trivy: A vulnerability scanner that can analyze images for known security issues.
• Docker Bench for Security: A script that checks for dozens of common best practices around deploying Docker containers in production.

How This Practice Applies to Different Migration Types

• Cloud Migration: When moving to cloud services, hardening images ensures that only secure, verified containers are deployed.
• Database Migration: Containers used for database services should also follow hardening practices to prevent unauthorized access.
• SaaS Migration: For SaaS platforms, using hardened images can protect sensitive data and improve compliance.
• Codebase Migration: When migrating code, ensure that the container images used for deployment are secure and minimal.

Checklist or Summary of Key Actions

• Start with a minimal base image
• Run containers as a non-root user
• Limit installed packages to essentials only
• Implement image signing
• Generate and maintain an SBOM
• Regularly update images to address vulnerabilities

By following these steps, you can ensure a secure and efficient containerization process that enhances the overall integrity of your applications.