Docker Image Security Risks

TL;DR

Running Docker images from untrusted sources can be risky. This guide explains common attack vectors and how to protect your system.

Understanding the Risks

Untrusted Docker images are a potential gateway for attackers. They can contain malicious code that compromises your host machine or network. Here’s what you need to know:

1. Image Source & Verification

1. Only use trusted registries: Prefer official repositories like Docker Hub (but even there, be cautious) and verified publishers.
2. Check image tags: Understand the tag’s meaning. Tags like latest are often mutable and less reliable than specific version numbers.
3. Verify publisher signatures: If available, verify the image’s signature to ensure it hasn’t been tampered with. Docker Content Trust (DCT) can help with this.

   docker trust inspect :

2. Container Privileges

1. Run containers as non-root: Avoid running containers with root privileges whenever possible. Use the USER instruction in your Dockerfile or the --user flag when running.

   docker run --user : :

2. Limit capabilities: Drop unnecessary Linux capabilities. Capabilities grant containers specific privileges; remove those not required.

   docker run --cap-drop ALL --cap-add NET_BIND_SERVICE :

3. Avoid privileged mode: Never run containers in --privileged mode unless absolutely necessary. This gives the container almost full access to the host system.

3. Network Security

1. Use network policies: Restrict network access for containers. Allow only necessary communication between containers and external networks. Tools like Docker’s networking features or third-party network policy engines can help.
2. Port mapping: Carefully consider which ports you expose from the container to the host. Only expose essential ports.

   docker run -p 8080:80 :

3. Firewall rules: Implement firewall rules on your host system to control inbound and outbound traffic to containers.

4. Filesystem Access

1. Read-only root filesystem: Mount the container’s root filesystem as read-only to prevent modifications.

   docker run --read-only :

2. Volume mounts: Be cautious with volume mounts. Avoid mounting sensitive host directories into containers unless absolutely necessary. If you must, ensure appropriate permissions are set.
3. Tmpfs mounts: Use tmpfs mounts for temporary files to avoid writing data to the persistent filesystem.

   docker run --mount type=tmpfs,destination=/tmp :

5. Image Scanning

1. Scan images for vulnerabilities: Use image scanning tools (e.g., Trivy, Clair, Snyk) to identify known security vulnerabilities in the image’s layers and dependencies.

   trivy image :

2. Automate scans: Integrate image scanning into your CI/CD pipeline to automatically detect vulnerabilities before deploying images.

6. Resource Limits

1. Set resource limits (CPU, memory): Limit the amount of CPU and memory a container can consume to prevent denial-of-service attacks or resource exhaustion.

   docker run --memory 512m --cpu-shares 512 :

7. Monitoring & Logging

1. Monitor container activity: Monitor containers for suspicious behavior, such as unexpected network connections or file modifications.
2. Centralized logging: Collect and analyze container logs to detect potential security incidents.

8. cyber security Best Practices

Regularly update Docker itself and the underlying host operating system with the latest security patches.