Docker: some tips about security 

Risk Areas

  • Host security
  • Client <> Daemon communication
  • Daemon security
  • Communication with public/private registry
  • Images
  • Containers
  • Registry’s security

Life cycle of an image

_dockerfile_ ==BUILD==>> _image_ ==SPIN==> Container
             maintaining images securely

Dockerfile Security

  • Do not write secrets in your dockerfile. Use some secret management solution like Hashicorp Vault.
  • Create a USER to executes the processes in the image, otherwise the container will run as root.
  • Avoid to use the latest tag. Better use version pinnin to avoid cache issues.
  • Remove unnecessary setuid, setgid permissions.
  • Do not write any kind of update instructions. All the layers are cached and this not assure the execution of the update.
  • Download packages securely and do not download unnecessary packages. Reduce your attack surface.
  • Use COPY instead of ADD to reduce the attack surface. add-or-copy
  • Use HEALTHCHECK command. Reducing Deploy Risk With Docker’s New Health Check Instruction Test-drive Docker Healthcheck in 10 minutes
  • Use gosu instead of sudo wherever is possible gosu.
  • Try to restrict a image/container to one single service.

Maintaining and Consuming Images

  • Docker Content Trust

    • provides authenticity, integrity and freshness guarantees.
    • takes some time to understand and prepare
  • Vulenrability free images:

    • tool selection: binary level analysis + hash based
    • Twistlock, Scalock, Nautilus to use only signed images, scan images, automatic container profiling.
    • aquasec
  • Except compatibility issues, all images and packages must be up-to-date.

Advanced Security (production/enterprise zone)

  • Do not use Docker hub Images. High possibility of malicious images.
  • Maintain your own in-house registries.
  • Perform image optimization techniques.
  • Use commercial tools:
    • Image Lockdown
    • RBAC
  • Use file monitoring solutions to monitor any malicious changes in image layers.
  • Have separate patch, vulnerability management procedures for containers.
  • Customize CIS Docker benchmarks.

Container Runtime

Some Docker defaults to consider

  • Containers can consume entire memory causeing DOS.
  • Containers can communicate with each other leading to sniffing etc.
  • Containers are on the same bridge leading ARP spoofing, MITM, etc.
  • Containers have no fork limit causing fork bomb.
  • Containers run as root.
  • Docker daemon access users have effective root privileges


  • Namespaces: beware of non-namespaced kernel keyrings: SYS_TIME, etc. Do not share namespaces unless really needed.
  • Seccomp
  • LSM’s SELinux and Apparmor
  • Capabilities: do not use privileged containers and try to set flag for not acquiring any additional privileges.