Testing Docker Images Security

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Testing Docker Images Security Bsides Manchester, August 2017

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Jose Manuel Ortega Software Engineer & Security Researcher @jmortegac jmortega.github.io

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Agenda ● Introduction to docker security ● Security best practices ● Tools for auditing docker images

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Docker ● “Docker containers wrap up a piece of software in a complete filesystem that contains everything it needs to run: code, runtime, system tools, system libraries – anything you can install on a server. This guarantees that it will always run the same, regardless of the environment it is running in.”

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Docker Security ● Docker provides an additional layer of isolation, making your infrastructure safer by default. ● Makes the application lifecycle fast and easier,reducing risks in your applications

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Docker Security ● Docker uses several mechanisms for security: ○ Linux kernel namespaces ○ Linux Control Groups (cgroups) ○ The Docker daemon ○ Linux capabilities (libcap) ○ Linux security mechanisms like AppArmor or SELinux

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Docker Security ● Namespaces:provides an isolated view of the system where processes cannot see other processes in other containers ● Each container also gets its own network stack. ● A container doesn’t get privileged access to the sockets or interfaces of another container.

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Docker Security ● Cgroups: kernel feature that limits and isolates the resource usage(CPU,memory,network) of a collection of processes. ● Linux Capabilities: divides the privileges of root into distinct units and smaller groups of privileges.

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DockerHub

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DockerFile https://github.com/CenturyLinkLabs/dockerfile-from-image

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Docker images ● Images are extracted in a chrooted sub process, being the first-step in a wider effort toward privilege separation. ● From Docker 1.10, all images are stored and accessed by the cryptographic checksums of their contents, limiting the possibility of an attacker causing a collision with an existing image Docker Content Trust.

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Docker Content Trust ● Protects against untrusted images ● Can enable signing checks on every managed host ● Signature verification transparent to users ● Guarantee integrity of your images when pulled ● Provides trust from publisher to consumer ● export DOCKER_CONTENT_TRUST=1 ● ~/.docker/trust/trusted-certificates/

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Security Best Practices

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DockerFile Security ● Do not write secrets(users and passwords). ● Remove unnecessary setuid, setgid permissions (Privilege escalation) ● Download packages securely using GPG and certificates ● Try to restrict an image or container to one service

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Security best practices ● To disable setuid rights, add the following to the Dockerfile of your image

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Security best practices ● Don’t run containers with --privileged flag ● The --privileged flag gives all capabilities to the container. ● docker run --privileged ... ● docker run --cap-drop=ALL --cap-add=CAP_NET_ADMIN ...

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Security best practices capabilities ● How do we add/remove capabilities? ● Use cap-add and cap-drop with docker run/create ● Drop all capabilities which are not required ● docker run --cap-drop ALL --cap-add $CAP

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Security best practices capabilities ● Manual management within the container: docker run --cap-add ALL ● Restricted capabilities with root: docker run --cap-drop ALL --cap-add $CAP ● No capabilities: docker run --user

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Security best practices capabilities

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Security best practices ● Set a specific user. ● Don’t run your applications as root in containers.

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Security best practices ● We can verify the integrity of the image ● Checksum validation when pulling image from docker hub ● Pulling by digest to enforce consistent

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Security best practices ● Check packages installed in the container

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Docker security is about limiting and controlling the attack surface on the kernel.

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Docker least privileges ● Do not run processes in a container as root to avoid root access from attackers. ● Enable User-namespace (disabled by default) ● Run filesystems as read-only so that attackers can not overwrite data or save malicious scripts to the image. ● Cut down the kernel calls that a container can make to reduce the potential attack surface. ● Limit the resources that a container can use (SELinux/AppArmor)

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Containers and volumes read-only 15

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Checklist Dockerfile

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Checklist building/maintaining/consuming

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AUDITING TOOLS

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Docker images scanning ● You can scan your images for known vulnerabilities ● There are tools for that, like Docker Security Scanning, Docker Bench Security and CoreOS Clair ● Find known vulnerable binaries

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Docker Security Scanning https://docs.docker.com/docker-cloud/builds/image-scan/ ● Checks based on best practices for hosts and containers ● Find Common Vulnerabilities and Exposures (CVEs)

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Docker Security Scanning ● Checks against CVE database for image layers ● Binary scanning of all components in the image ● Performs binary scan to pick up on statically linked binaries ● Analyses libraries statically compiled in the image ● Generates a reports that shows if there are CVE in the libraries inside the image

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Docker Security Scanning 15 25

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Docker Security Scanning

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Docker CVE https://www.docker.com/docker-cve-database

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Security pipeline

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Clair (Container Vulnerability Analysis Service) https://github.com/coreos/clair Vulnerability Static Analysis for Containers

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Clair Use cases ● You've found an image by searching the internet and want to determine if it's safe enough for you to use in production. ● You're regularly deploying into a containerized production environment and want operations to alert or block deployments on insecure software.

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Docker Bench Security https://github.com/docker/docker-bench-security Checks based on best practices for hosts and containers

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Docker bench security ● Open-source tool for running automated tests ● Inspired by the CIS Docker 1.11 benchmark ● Runs against containers currently running on same host ● Checks for AppArmor, read-only volumes, etc...

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Docker bench security

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Docker bench security ● The host configuration ● The Docker daemon configuration ● The Docker daemon configuration files ● Container images and build files ● Container runtime ● Docker security operations

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Docker bench security ● The Docker daemon configuration ● [WARN] 2.1- Restrict network traffic between containers ● [WARN] 4.1 - Create a user for the container [WARN] * Running as root: ● [WARN] 5.4 - Restrict Linux Kernel Capabilities within containers [WARN] * Capabilities added: CapAdd=[audit_control] ● [WARN] 5.13 - Mount container's root filesystem as readonly [WARN] * Container running with root FS mounted R/W:

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Docker Slim https://github.com/docker-slim/docker-slim Optimize and secure your Docker containers

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Other tools ● OpenSCAP Container Compliance ● Lynis ● Twistlock ● Dockscan ● Aqua Security ● Dagda

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OpenScap Clair Lynis TwistLock DockScan Images and Containers Images and Containers DockerFile Images, containers, packages. Kubernetes Mesos. Docker server RedHat /Fedora /CentOS based containers Debian /Ubuntu /CentOS based containers Linux and Unix based Systems Linux and Unix based Systems Docker and container installations

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Lynis ● Lynis is a Linux, Mac and Unix security auditing and system hardening tool that includes a module to audit Dockerfiles. ● lynis audit dockerfile

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● https://github.com/CISOfy/lynis-docker

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Dagda ● Static analysis of known vulnerabilities on Docker containers ● Allows monitoring Docker containers for detecting anomalous activities

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Dagda ● Python 3 ● MongoDB ● PyMongo ● Requests ● Python-dateutil ● Joblib ● Docker-py ● Flask ● Flask-cors ● PyYAML

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● python3 dagda.py check --docker_image ● python3 dagda.py history --id

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Conclusions Signing ● Secure & sign your source Dependences ● Pin & verify your dependencies Content Trust ● Sign your artifacts with Docker Content Trust Privileges ● Least Privilege configurations

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References ● https://docs.docker.com/engine/security ● http://www.oreilly.com/webops-perf/free/files/dock er-security.pdf ● http://container-solutions.com/content/uploads/201 5/06/15.06.15_DockerCheatSheet_A2.pdf ● https://www.openshift.com/promotions/docker-sec urity.html

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References ● Docker Content Trust ● https://docs.docker.com/engine/security/trust/content_trust ● Docker Security Scanning ● https://docs.docker.com/docker-cloud/builds/image-scan ● https://blog.docker.com/2016/04/docker-security ● http://softwaretester.info/docker-audit/

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