Docker Hub: Are Verified Publisher Images Secure?

TL;DR

Verified publisher images on Docker Hub are generally safer than unverified ones, but they aren’t a guarantee of complete security. You still need to take steps to check what you’re running and keep it updated. This guide explains how.

Understanding the Risks

Docker containers, even from verified publishers, can contain vulnerabilities. These could be in the application itself, or in the base image they’re built on. A compromised container can lead to data breaches, service disruption, or other cyber security incidents.

Steps to Secure Verified Publisher Docker Images

1. Check the Image’s Details: Before pulling an image, review its information page on Docker Hub.
   • Tags: Look at the tags. Use specific version numbers instead of ‘latest’. ‘Latest’ can change unexpectedly.
   • Description: Read the description carefully to understand what the image contains and how it’s intended to be used.
   • Official Image Status: Verify that the publisher is actually an official one, even if it says “Verified”. Look for the official badge.
2. Scan for Vulnerabilities: Use a vulnerability scanner before running the container.
   • Trivy: A popular open-source scanner. Install with your package manager (e.g., apt install trivy on Debian/Ubuntu). Then scan:

     trivy image <image_name>

   • Docker Scan: Integrated into Docker Desktop and CLI (requires a Docker Hub account).

     docker scan <image_name>

3. Base Image Analysis: Understand the base image used.
   • Check Base Image History: Find out what layers are in the base image. This helps identify potential vulnerabilities inherited from older software.

     docker history <image_name>

   • Use Minimal Base Images: Alpine Linux or distroless images are smaller and have fewer packages, reducing the attack surface.
4. Regular Updates: Keep your images up-to-date.
   • Automated Builds: Use Docker Hub’s automated build feature to rebuild images when the base image is updated (if available).
   • Scheduled Scans: Regularly scan running containers and update them if vulnerabilities are found.
5. Least Privilege Principle: Run containers with minimal privileges.
   • User Permissions: Don’t run containers as root unless absolutely necessary. Create a dedicated user within the container.
   • Capabilities: Drop unnecessary Linux capabilities using --cap-drop ALL and add only required ones with --cap-add <capability>.
6. Network Policies: Restrict network access.
   • Firewall Rules: Configure firewalls to allow only necessary inbound and outbound traffic for the container.
   • Container Networking: Use Docker’s networking features to isolate containers from each other.
7. Image Signing (Docker Content Trust): Verify image integrity.
   • Enable DCT: This ensures the image hasn’t been tampered with during transit or storage. Requires configuration on both publisher and consumer sides. See Docker documentation for details.

Important Considerations

Verified publishers are vetted by Docker, but this doesn’t mean their images are flawless. They can still contain bugs or vulnerabilities. Always practice defence in depth and treat all containers as potentially untrusted until proven otherwise.