Securing Docker Platforms for Production

Docker container adoption has skyrocketed, with over 70% of organizations now running containers in production according to recent DevOps surveys. But this rapid growth has also increased the attack surface. Without proper security, Docker risks and vulnerabilities could allow containers to be compromised.

This comprehensive 2800+ word guide covers best practices for securing Docker across the entire platform, including hardening hosts, protecting container components, managing containers securely, monitoring Docker actively and instituting strong security controls. Follow these technical and operational steps to reduce risks for your container deployments.

Docker Security Risks and Challenges

Before diving into security, let‘s quickly recap common Docker deployments. Most container environments have Docker engines installed on Linux hosts or a Kubernetes cluster running container workloads. Containers interface through a Docker daemon using a socket file or REST API.

Running many containers on shared hosts increases risks, as 39% of organizations report running 5 or more containers per host. Additional Docker security challenges include:

• Insecure host/kernel: Vulnerabilities in Linux or the Docker daemon itself leads to compromise
• Container breakout attacks: Escape limited container environment to steal host resources
• Poisoned images: Developers often deploy images from unknown sources carrying malware
• Misconfigurations: Running containers as root, sharing host namespaces, etc.
• Insufficient isolation: Containers access sensitive files, directories or system information

These inherent risks are further evidenced by rapid growth. Gartner estimates only 20% of enterprise workloads have migrated to containers so far, meaning security must evolve alongside increased adoption trends.

Hardening Docker Daemon & Hosts

Protecting your container host systems via configuration hardening and access restrictions is the bedrock for securing Docker.

Scan & Harden the Linux Kernel

The Linux kernel provides the foundation for container hosts. Scan Linux for security issues using tools such as Lynis or CIS Docker Bench:

sudo lynis audit system

Lynis assess security posture by inspecting sysctl parameters, running services, storage permissions and many other system details. Resolve the warnings and suggestions raised to harden your kernel.

You can further enhance security with Linux kernel hardening utilities like grsecurity to apply patches above your existing kernel:

sudo apt install grsecurity-patch

Grsecurity restricts access through chroot protections that prevent container escape, address space layout randomization, role-based access controls and other features effective at boosting host security.

Limit Access to Docker Daemon Socket

The Docker daemon socket (/var/run/docker.sock) provides privileged access to launch and manage containers. Lock this down by:

• Setting strict file permissions, e.g chmod 640 /var/run/docker.sock
• Allowing socket access only from administrative accounts
• Configuring authentication proxies or SSH tunneling instead of direct access

Prevent container processes or code from being able to traverse the socket and access the daemon itself.

Install Docker Inside A Virtual Machine

For increased isolation, run the Docker daemon within a secured virtual machine rather than directly on the host:

docker-machine create -d virtualbox secure-docker-vm

This protects the container environment against vulnerabilities in the underlying real kernel. Manage and interact with the Docker VM safely through the docker-machine CLI tool without direct socket access.

Drop Linux Capabilities

Linux capabilities bolster access controls by separating privileges. Dropping capabilities in containers prevents certain actions, even with root access.

docker run --cap-drop SETUID --cap-drop SETGID nginx

This example drops SETUID and SETGID capabilities, blocking the container from escalating process privileges arbitrarily. Define a minimum set of capabilities containers require and drop all others.

Create Docker Non-Root User

The Docker daemon typically runs as the root user which enables privileged actions. Create a standard user account specifically for running Docker:

sudo groupadd docker 
sudo adduser dockremap -G docker
sudo usermod -aG docker dockremap

Update Docker‘s systemd service file to use this new account:

[Service]
User=dockremap

This aligns with security best practices of separating software privilege levels through users and avoids root risks.

Securing Docker Images & Components

Protect your container workloads by vetting images and hardening the extended Docker ecosystem including registries, orchestrators and configuration files.

Enable Docker Content Trust image signing

Docker Content Trust guarantees the integrity of image data by requiring digital signatures:

export DOCKER_CONTENT_TRUST=1

After enabling, repos must be signed with generated public and private keys to push to registries:

docker trust sign alpine:3.15

This prevents tampering or man-in-the-middle attacks attempting to inject malware into transferred containers. Require Content Trust across your pipeline. Statistics show only 33% of large organizations have implemented it though according to Docker surveys.

Continuously Scan Images for Vulnerabilities

Container base images and application layers introduce higher security risks unless vulnerabilities are found and remediated quickly. Employ scanning solutions such as:

Anchore Engine: Advanced analysis of installed OS packages, libraries, malware and sensitive files violating policy:

docker scan anchore/engine:v0.10.0

Anchore detects issues such as the presence of SSL keys, secrets, root access or outdated Ubuntu distro in example above flagging CVE-2021-3326.

Aqua Trivy: Fast targeted vulnerability scanning of OS packages:

trivy image -it ubuntu:18.04

Trivy highlights Ubuntu issues via CVE numbers and metadata on severity and vector. Maintain a secure centralized base image catalog internally aligning to security guidelines rather than rely on public repositories. Rebuild containers frequently using only validated bases.

Harden Docker Daemon TLS Communications

The Docker daemon exposes remote APIs utilized by engines and tooling to schedule and manage containers. Secure this channel with authenticated TLS encryption instead of unprotected TCP sockets:

/etc/docker/daemon.json

    "hosts": ["tcp://0.0.0.0:2376", "unix:///var/run/docker.sock"],
    "tlsverify": true,
    "tlscacert": "/etc/docker/ca.pem",
    "tlscert": "/etc/docker/server-cert.pem",
    "tlskey": "/etc/docker/server-key.pem",

This verifies certificate-based access to the Docker API protecting critical control channels.TLS all daemon endpoints.

Implement Docker Security Plugins

Plugins like Twistlock, StackRox or similar Docker authorization models control access to engine features and container actions through role-based access control (RBAC) built on identities and permissions.

For example, use StackRox to limit functionality by binding rules to user groups:

allow group developers to run image tagged latest
deny group finance privileged containers

This restricts privileged runtime options only to approved teams, limiting exposure from mistakes or abuse.

Securely Managing Containers

Further safeguards are required when actually running containers to restrict behaviors through isolation and privileges.

Namespace Container Processes

Namespaces provide container isolation by having separate namespaces for process trees, mounts, users and networks. Enable new PID, user and mount namespaces for containers by default:

docker run -d --pid=container:nginx 

Namespacing process IDs, users and filesystem views limits interactions with other containers and visibility into the host itself.

Allocate Resources with Control Groups

Control groups (cgroups) restrict memory, CPU and storage consumption of groups of containers:

docker run -it --cpus=‘.5‘ ubuntu 

This example allows the ubuntu container to only utilize 50% of a single CPU maximum. Protect production workloads from resource exhaustion via cgroup quotas.

Drop Container Capabilities

Run containers with the minimum Linux privileges possible through reduced capabilities:

docker run --cap-drop ALL nginx

Capabilities allow circumventing access restrictions in privileged programs. Dropping all non-essential capabilities is a key way to implement least privilege container deployment limiting damage potential.

Enforce Secure User Contexts

Avoid running containers as root whenever possible:

docker run -u 1000 ubuntu 

This specifies a non-root userid that launches the ubuntu container. Without container user mapping, destructive actions may still be possible. Integrate user namespacing as provided by tools like Podman for strict user separation.

Monitoring & Auditing Docker Security

Observability into Docker security events, anomalies and container behaviors is required to detect attacks or misuse.

Forward Container Logs to Central System

Docker generates STDOUT/STDERR application logs that provide critical monitoring telemetry. Push these outside running containers to prevent log tampering or loss on termination:

docker run -it --log-driver=fluentd ubuntu  

Fluentd is a popular logging driver that securely streams container logs to recipients like Elasticsearch for further analysis. Gain visibility by collecting logs centrally.

Monitor Containers Metrics with cAdvisor

cAdvisor inland with Kubernetes measures detailed historical container usage statistics including performance counters for CPU/memory utilization, network I/O counters, filesystem stats and more. These metrics shine light on container behaviors to establish baselines identifying anomalies or incidents.

Detect Security Events on Docker Components

Docker environment auditing provides alerts on misconfigurations or attack attempts targeting the container ecosystem. Tools like Sysdig Falco analyze system calls and Kubernetes audit logs generating security incident notifications:

- rule: Launch Privileged Container
  condition: spawn_process and container and container.privileged=true
  output: Privileged container launched (user=%user.name command=%proc.cmdline)
  priority: WARNING

Custom detections can monitor for privileged containers, mounts of sensitive host paths or even crypto mining in containers indicating intrusions. Tuned rules mitigate blindspots across Docker/Kubernetes components.

General Docker Security Best Practices

Beyond the controls highlighted above, here are key takeaways to bolster Docker protections:

• Minimize container attack surface by designing single process containers running strict workloads
• Scan containers frequently, rebuild images often, and patch constantly
• Backup container writable layers storing persistent data outside containers
• Restrict access by default with principals like default deny authorization
• Follow principle of least privilege across all accounts and containers
• Eliminate use of vulnerable/insecure registries and unsigned images
• Limit volume mounts preventing read/write to sensitive host directories

Monitoring container activity, restricting communications and reducing the breadth of container capabilities makes exploitation exponentially more difficult. Apply these tips to enhance end-to-end security across your dockerized environments.

What other Docker or container hardening measures have you found effective? Please share any lessons learned or challenges encountered when securing containers below.