dockle

Dockle is Security auditing tool that helps you

1. Build secure Docker images
   • Checkpoints includes CIS Benchmarks
2. Build Best Practice Docker images

You can check a docker image only run...

dockle [YOUR_IMAGE_NAME]

TOC

• Comparison
• Installation
  • RHEL/CentOS
  • Debian/Ubuntu
  • Mac OS X / Homebrew
  • Binary (Including Windows)
  • From source
• Checkpoint Summary
• Quick Start
  • Basic
  • Docker
• Examples
  • Scan an image
  • Scan an image file
  • Specify exit code
  • Ignore the specified checkpoints
  • Clear image caches
• Continuous Integration
  • Travis CI
  • CircleCI
  • Authorization for Private Docker Registry
• Checkpoint Detail
  • CIS's Docker Image Checkpoints
  • Dockle Checkpoints for Docker
  • Dockle Checkpoints for Linux
• Credits
• Roadmap

Comparison (use CIS Benchmark checkpoints)

All checkpoints here!

Installation

RHEL/CentOS

$ rpm -ivh https://github.com/goodwithtech/dockle/releases/download/v0.0.14/dockle_0.0.14_Linux-64bit.rpm

Debian/Ubuntu

$ wget https://github.com/goodwithtech/dockle/releases/download/v0.0.14/dockle_0.0.14_Linux-64bit.deb
$ sudo dpkg -i dockle_0.0.14_Linux-64bit.deb

Mac OS X / Homebrew

You can use homebrew on Mac OS.

$ brew tap goodwithtech/dockle 
$ brew install goodwithtech/dockle/dockle

Binary (Including Windows)

Get the latest version from this page, and download the archive file for your operating system/architecture. Unpack the archive, and put the binary somewhere in your $PATH (on UNIX-y systems, /usr/local/bin or the like). Make sure it has execution bits turned on.

From source

$ go get -u github.com/goodwithtech/dockle

Quick Start

Basic

Simply specify an image name (and a tag).

$ dockle [YOUR_IMAGE_NAME]

FATAL   - Create a user for the container
        * Last user should not be root
WARN    - Enable Content trust for Docker
        * export DOCKER_CONTENT_TRUST=1 before docker pull/build
FATAL   - Add HEALTHCHECK instruction to the container image
        * not found HEALTHCHECK statement
FATAL   - Do not use update instructions alone in the Dockerfile
        * Use 'apt-get update --no-cache' : /bin/sh -c apt-get update && apt-get install -y git
PASS    - Remove setuid and setgid permissions in the images
FATAL   - Use COPY instead of ADD in Dockerfile
        * Use COPY : /bin/sh -c #(nop) ADD file:81c0a803075715d1a6b4f75a29f8a01b21cc170cfc1bff6702317d1be2fe71a3 in /app/credentials.json
FATAL   - Do not store secrets in ENVIRONMENT variables
        * Suspicious ENV key found : MYSQL_PASSWD
FATAL   - Do not store secret files
        * Suspicious filename found : app/credentials.json
PASS    - Avoid sudo command
FATAL   - Avoid sensitive directory mounting
        * Avoid mounting sensitive dirs : /usr
PASS    - Avoid apt-get/apk/dist-upgrade
PASS    - Use apk add with --no-cache
FATAL   - Clear apt-get caches
        * Use 'apt-get clean && rm -rf /var/lib/apt/lists/*' : /bin/sh -c apt-get update && apt-get install -y git
PASS    - Avoid latest tag
FATAL   - Avoid empty password
        * No password user found! username : nopasswd
PASS    - Be unique UID
PASS    - Be unique GROUP

Docker

Replace [YOUR_CACHE_DIR] with the cache directory on your machine.

$ docker run --rm -v [YOUR_CACHE_DIR]:/root/.cache/ goodwithtech/dockle [YOUR_IMAGE_NAME]

Example for macOS:

$ docker run --rm -v $HOME/Library/Caches:/root/.cache/ goodwithtech/dockle [YOUR_IMAGE_NAME]

If you would like to scan the image on your host machine, you need to mount docker.sock.

$ docker run --rm -v /var/run/docker.sock:/var/run/docker.sock ...

Please re-pull latest goodwithtech/dockle if an error occured.

Checkpoint Summary

Level

Dockle has 5 check levels

Examples

Scan an image

Simply specify an image name (and a tag).

$ dockle goodwithtech/test-image:v1

FATAL   - CIS-DI-0001: Create a user for the container
        * Last user should not be root
WARN    - CIS-DI-0005: Enable Content trust for Docker
        * export DOCKER_CONTENT_TRUST=1 before docker pull/build
FATAL   - CIS-DI-0006: Add HEALTHCHECK instruction to the container image
        * not found HEALTHCHECK statement
FATAL   - CIS-DI-0007: Do not use update instructions alone in the Dockerfile
        * Use 'apt-get update --no-cache' : /bin/sh -c apt-get update && apt-get install -y git
FATAL   - CIS-DI-0008: Remove setuid and setgid permissions in the images
        * Found setuid file: etc/passwd grw-r--r--
        * Found setuid file: usr/lib/openssh/ssh-keysign urwxr-xr-x
        * Found setuid file: app/hoge.txt ugrw-r--r--
        * Found setuid file: app/hoge.txt ugrw-r--r--
        * Found setuid file: etc/shadow urw-r-----
FATAL   - CIS-DI-0009: Use COPY instead of ADD in Dockerfile
        * Use COPY : /bin/sh -c #(nop) ADD file:81c0a803075715d1a6b4f75a29f8a01b21cc170cfc1bff6702317d1be2fe71a3 in /app/credentials.json
FATAL   - CIS-DI-0010: Do not store secrets in ENVIRONMENT variables
        * Suspicious ENV key found : MYSQL_PASSWD
FATAL   - CIS-DI-0010: Do not store secret files
        * Suspicious filename found : app/credentials.json
PASS    - DKL-DI-0001: Avoid sudo command
FATAL   - DKL-DI-0002: Avoid sensitive directory mounting
        * Avoid mounting sensitive dirs : /usr
PASS    - DKL-DI-0003: Avoid apt-get/apk/dist-upgrade
PASS    - DKL-DI-0004: Use apk add with --no-cache
FATAL   - DKL-DI-0005: Clear apt-get caches
        * Use 'apt-get clean && rm -rf /var/lib/apt/lists/*' : /bin/sh -c apt-get update && apt-get install -y git
PASS    - DKL-DI-0006: Avoid latest tag
FATAL   - DKL-LI-0001: Avoid empty password
        * No password user found! username : nopasswd
PASS    - DKL-LI-0002: Be unique UID
PASS    - DKL-LI-0002: Be unique GROUP

Scan an image file

$ docker save alpine:latest -o alpine.tar
$ dockle --input alpine.tar

Specify exit code

By default, Dockle exits with code 0 even if there are some problems. Use the --exit-code option if you want to exit with a non-zero exit code.

$ dockle  -exist-code 1 [IMAGE_NAME]

Ignore the specified checkpoints (only work with --exit-code)

Use .dockleignore.

$ cat .dockleignore
# set root to default user because we want to run nginx
CIS-DI-0001
# Use latest tag because only check for image inside
DKL-DI-0006

Clear image caches

The --clear-cache option removes image caches. This option is useful if the image which has the same tag is updated (such as when using latest tag).

$ dockle --clear-cache python:3.7

Continuous Integration (CI)

Scan your image built in Travis CI/CircleCI. The test will fail with if a error is found. You can skip target checkpoint if you use .dockleignore.

When you don't want to fail the test, specify --exit-code 0.

Travis CI

services:
  - docker

env:
  global:
    - COMMIT=${TRAVIS_COMMIT::8}

before_install:
  - docker build -t dockle-ci-test:${COMMIT} .
  - export VERSION=$(curl --silent "https://api.github.com/repos/goodwithtech/dockle/releases/latest" | grep '"tag_name":' | sed -E 's/.*"v([^"]+)".*/\1/')
  - wget https://github.com/goodwithtech/dockle/releases/download/v${VERSION}/dockle_${VERSION}_Linux-64bit.tar.gz
  - tar zxvf dockle_${VERSION}_Linux-64bit.tar.gz
script:
  - ./dockle dockle-ci-test:${COMMIT}
  - ./dockle --exit-code 1 dockle-ci-test:${COMMIT}

Example: https://travis-ci.org/goodwithtech/dockle-ci-test
Repository: https://github.com/goodwithtech/dockle-ci-test

CircleCI

jobs:
  build:
    docker:
      - image: docker:18.09-git
    steps:
      - checkout
      - setup_remote_docker
      - run:
          name: Build image
          command: docker build -t dockle-ci-test:${CIRCLE_SHA1} .
      - run:
          name: Install dockle
          command: |
            apk add --update curl
            VERSION=$(
                curl --silent "https://api.github.com/repos/goodwithtech/dockle/releases/latest" | \
                grep '"tag_name":' | \
                sed -E 's/.*"v([^"]+)".*/\1/'
            )

            wget https://github.com/goodwithtech/dockle/releases/download/v${VERSION}/dockle_${VERSION}_Linux-64bit.tar.gz
            tar zxvf dockle_${VERSION}_Linux-64bit.tar.gz
            mv dockle /usr/local/bin
      - run:
          name: Scan the local image with dockle
          command: dockle --exit-code 1 dockle-ci-test:${CIRCLE_SHA1}
workflows:
  version: 2
  release:
    jobs:
      - build

Example : https://circleci.com/gh/goodwithtech/dockle-ci-test
Repository: https://github.com/goodwithtech/dockle-ci-test

Authorization for Private Docker Registry

Dockle can download images from private registry, without installing Docker and any 3rd party tools. That's because it's easy to run in a CI process.

All you have to do is install Dockle and set ENVIRONMENT variables. But, I can't recommend using ENV vars in your local machine to you.

Docker Hub

Docker Hub needs DOCKLE_AUTH_URL, DOCKLE_USERNAME and DOCKLE_PASSWORD. You don't need to set ENV vars when download from public repository.

export DOCKLE_AUTH_URL=https://registry.hub.docker.com
export DOCKLE_USERNAME={DOCKERHUB_USERNAME}
export DOCKLE_PASSWORD={DOCKERHUB_PASSWORD}

Amazon ECR (Elastic Container Registry)

Dockle uses AWS SDK. You don't need to install aws CLI tool. You can use AWS CLI's ENVIRONMENT variables.

GCR (Google Container Registry)

Dockle uses Google Cloud SDK. You don't need to install gcloud command.

If you want to use target project's repository, you can settle via GOOGLE_APPLICATION_CREDENTIAL.

# must set DOCKLE_USERNAME empty char
export GOOGLE_APPLICATION_CREDENTIALS=/path/to/credential.json

Self Hosted Registry (BasicAuth)

BasicAuth server needs DOCKLE_USERNAME and DOCKLE_PASSWORD.

export DOCKLE_USERNAME={USERNAME}
export DOCKLE_PASSWORD={PASSWORD}

# if you want to use 80 port, use NonSSL
export DOCKLE_NON_SSL=true

Checkpoint Detail

Docker Image Checkpoints

These checkpoints refered to CIS Docker 1.13.0 Benchmark v1.0.0.

CIS-DI-0001: Create a user for the container

Create a non-root user for the container in the Dockerfile for the container image.

# Dockerfile
RUN useradd -d /home/username -m -s /bin/bash username
USER username

CIS-DI-0002: Use trusted base images for containers

Not supported. Please check with Trivy.

CIS-DI-0003: Do not install unnecessary packages in the container

Not supported yet.

CIS-DI-0004: Scan and rebuild the images to include security patches

Not supported. Please check with Trivy.

CIS-DI-0005: Enable Content trust for Docker

Content trust is disabled by default. You should enable it.

$ export DOCKER_CONTENT_TRUST=1 

https://docs.docker.com/engine/security/trust/content_trust/#about-docker-content-trust-dct

Docker Content Trust (DCT) provides the ability to use digital signatures for data sent to and received from remote Docker registries. Engine Signature Verification prevents the following:

• $ docker container run of an unsigned image.
• $ docker pull of an unsigned image.
• $ docker build where the FROM image is not signed or is not scratch.

CIS-DI-0006: Add HEALTHCHECK instruction to the container image

Add HEALTHCHECK instruction in your docker container images to perform the health check on running containers.

# Dockerfile
HEALTHCHECK --interval=5m --timeout=3s \
  CMD curl -f http://localhost/ || exit 1

CIS-DI-0007: Do not use update instructions alone in the Dockerfile

Do not use update instructions such as apt-get update alone or in a single line in the Dockerfile.

RUN apt-get update --no-cache

CIS-DI-0008: Remove setuid and setgid permissions in the images

Removing setuid and setgid permissions in the images would prevent privilege escalation attacks in the containers.

chmod u-s setuid-file
chmod u-g setgid-file

CIS-DI-0009: Use COPY instead of ADD in Dockerfile

Use COPY instruction instead of ADD instruction in the Dockerfile.

# Dockerfile
ADD test.json /app/test.json
↓
COPY test.json /app/test.json

CIS-DI-0010: Do not store secrets in Dockerfiles

Do not store any secrets in Dockerfiles.

Dockle checks ENVIRONMENT variables and credential files.

CIS-DI-0011: Install verified packages only

Not supported. It's better to use Trivy.

Dockle Checkpoints for Docker

These checkpoints refered to Docker Best Practice and so on.

DKL-DI-0001: Avoid sudo command

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#user

Avoid installing or using sudo as it has unpredictable TTY and signal-forwarding behavior that can cause problems.

DKL-DI-0002: Avoid sensitive directory mounting

A volume mount makes weakpoints. This depends on mounting volumes. Currently, Dockle checks following directories.

/boot,/dev,/etc,/lib,/proc,/sys, /usr

dockle only checks VOLUME statements. We can't check docker run -v /lib:/lib ....

DKL-DI-0003: Avoid apt-get upgrade, apk upgrade, dist-upgrade

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#apt-get

Avoid RUN apt-get upgrade and dist-upgrade, as many of the “essential” packages from the parent images cannot upgrade inside an unprivileged container.

DKL-DI-0004: Use apk add with --no-cache

https://github.com/gliderlabs/docker-alpine/blob/master/docs/usage.md#disabling-cache

As of Alpine Linux 3.3 there exists a new --no-cache option for apk. It allows users to install packages with an index that is updated and used on-the-fly and not cached locally: This avoids the need to use --update and remove /var/cache/apk/* when done installing packages.

DKL-DI-0005: Clear apt-get caches

Use “apt-get clearn && rm -rf /var/lib/apt/lists/*` if use apt-get install

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#apt-get

In addition, when you clean up the apt cache by removing /var/lib/apt/lists it reduces the image size, since the apt cache is not stored in a layer. Since the RUN statement starts with apt-get update, the package cache is always refreshed prior to apt-get install.

DKL-DI-0006: Avoid latest tag

https://vsupalov.com/docker-latest-tag/

Docker images tagged with :latest have caused many people a lot of trouble.

Dockle Checkpoints for Linux

These checkpoints refered to Linux Best Practices and so on.

DKL-LI-0001: Avoid empty password

https://blog.aquasec.com/cve-2019-5021-alpine-docker-image-vulnerability

CVE-2019-5021: Alpine Docker Image ‘null root password’ Vulnerability

DKL-LI-0002: Be unique UID/GROUPs

http://www.linfo.org/uid.html

Contrary to popular belief, it is not necessary that each entry in the UID field be unique. However, non-unique UIDs can cause security problems, and thus UIDs should be kept unique across the entire organization.

Credits

Special Thanks to @knqyf263 (Teppei Fukuda) and Trivy

License

AGPLv3

Author

@tomoyamachi (Tomoya Amachi)

Roadmap

• Check php.ini file
• Check nginx.conf file
• Check /etc/hosts
  • duplicates
  • hostname
  • localhost
• Packages
  • Package managers
• File Permissions
  • Insecure permission
• Image Size
  • check large size container

if running docker daemon...

• Networking
  • docker port container if docker running
  • by file
    • /proc/1/net/tcp : openning port (if running)
• Volume mount
  • mount dangerous
    • /boot, /dev, /etc, /lib