Container Scanning

Overview

Your application’s Docker image may itself be based on Docker images that contain known vulnerabilities. By including an extra job in your pipeline that scans for those vulnerabilities and displays them in a merge request, you can use GitLab to audit your Docker-based apps. By default, container scanning in GitLab is based on Clair and Klar, which are open-source tools for vulnerability static analysis in containers. GitLab’s Klar analyzer scans the containers and serves as a wrapper for Clair.

Note: To integrate security scanners other than Clair and Klar into GitLab, see Security scanner integration.

You can enable container scanning by doing one of the following:

GitLab compares the found vulnerabilities between the source and target branches, and shows the information directly in the merge request.

Container Scanning Widget

Requirements

To enable container scanning in your pipeline, you need the following:

  • GitLab Runner with the docker or kubernetes executor.
  • Docker 18.09.03 or higher installed on the same computer as the runner. If you’re using the shared runners on GitLab.com, then this is already the case.
  • Build and push your Docker image to your project’s container registry. The name of the Docker image should use the following predefined environment variables:

    $CI_REGISTRY_IMAGE/$CI_COMMIT_REF_SLUG:$CI_COMMIT_SHA
    

    You can use these directly in your .gitlab-ci.yml file:

    build:
      image: docker:19.03.12
      stage: build
      services:
        - docker:19.03.12-dind
      variables:
        IMAGE_TAG: $CI_REGISTRY_IMAGE/$CI_COMMIT_REF_SLUG:$CI_COMMIT_SHA
      script:
        - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
        - docker build -t $IMAGE_TAG .
        - docker push $IMAGE_TAG
    

Configuration

How you enable container scanning depends on your GitLab version:

To include the Container-Scanning.gitlab-ci.yml template (GitLab 11.9 and later), add the following to your .gitlab-ci.yml file:

include:
  - template: Container-Scanning.gitlab-ci.yml

The included template:

  • Creates a container_scanning job in your CI/CD pipeline.
  • Pulls the built Docker image from your project’s container registry (see requirements) and scans it for possible vulnerabilities.

GitLab saves the results as a Container Scanning report artifact that you can download and analyze later. When downloading, you always receive the most-recent artifact.

The following is a sample .gitlab-ci.yml that builds your Docker image, pushes it to the container registry, and scans the containers:

variables:
  DOCKER_DRIVER: overlay2

stages:
  - build
  - test

build:
  image: docker:stable
  stage: build
  services:
    - docker:19.03.12-dind
  variables:
    IMAGE: $CI_REGISTRY_IMAGE/$CI_COMMIT_REF_SLUG:$CI_COMMIT_SHA
  script:
    - docker info
    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
    - docker build -t $IMAGE .
    - docker push $IMAGE

include:
  - template: Container-Scanning.gitlab-ci.yml

Customizing the container scanning settings

There may be cases where you want to customize how GitLab scans your containers. For example, you may want to enable more verbose output from Clair or Klar, access a Docker registry that requires authentication, and more. To change such settings, use the variables parameter in your .gitlab-ci.yml to set environment variables. The environment variables you set in your .gitlab-ci.yml overwrite those in Container-Scanning.gitlab-ci.yml.

This example includes the container scanning template and enables verbose output from Clair by setting the CLAIR_OUTPUT environment variable to High:

include:
  - template: Container-Scanning.gitlab-ci.yml

variables:
  CLAIR_OUTPUT: High

Available variables

You can configure container scanning by using the following environment variables:

Environment Variable Default Description
ADDITIONAL_CA_CERT_BUNDLE "" Bundle of CA certs that you want to trust.
CLAIR_DB_CONNECTION_STRING postgresql://postgres:password@clair-vulnerabilities-db:5432/postgres?sslmode=disable&statement_timeout=60000 This variable represents the connection string to the PostgreSQL server hosting the vulnerabilities definitions database and shouldn’t be changed unless you’re running the image locally as described in the Running the standalone container scanning tool section. The host value for the connection string must match the alias value of the Container-Scanning.gitlab-ci.yml template file, which defaults to clair-vulnerabilities-db.
CLAIR_DB_IMAGE arminc/clair-db:latest The Docker image name and tag for the PostgreSQL server hosting the vulnerabilities definitions. It can be useful to override this value with a specific version, for example, to provide a consistent set of vulnerabilities for integration testing purposes, or to refer to a locally hosted vulnerabilities database for an on-premise offline installation.
CLAIR_DB_IMAGE_TAG latest (DEPRECATED - use CLAIR_DB_IMAGE instead) The Docker image tag for the PostgreSQL server hosting the vulnerabilities definitions. It can be useful to override this value with a specific version, for example, to provide a consistent set of vulnerabilities for integration testing purposes.
CLAIR_OUTPUT Unknown Severity level threshold. Vulnerabilities with severity level higher than or equal to this threshold are outputted. Supported levels are Unknown, Negligible, Low, Medium, High, Critical and Defcon1.
CLAIR_TRACE "false" Set to true to enable more verbose output from the clair server process.
CLAIR_VULNERABILITIES_DB_URL clair-vulnerabilities-db (DEPRECATED - use CLAIR_DB_CONNECTION_STRING instead) This variable is explicitly set in the services section of the Container-Scanning.gitlab-ci.yml file and defaults to clair-vulnerabilities-db. This value represents the address that the PostgreSQL server hosting the vulnerabilities definitions is running on and shouldn’t be changed unless you’re running the image locally as described in the Running the standalone container scanning tool section.
CI_APPLICATION_REPOSITORY $CI_REGISTRY_IMAGE/$CI_COMMIT_REF_SLUG Docker repository URL for the image to be scanned.
CI_APPLICATION_TAG $CI_COMMIT_SHA Docker repository tag for the image to be scanned.
DOCKER_INSECURE "false" Allow Klar to access secure Docker registries using HTTPS with bad (or self-signed) SSL certificates.
DOCKER_PASSWORD $CI_REGISTRY_PASSWORD Password for accessing a Docker registry requiring authentication.
DOCKER_USER $CI_REGISTRY_USER Username for accessing a Docker registry requiring authentication.
DOCKERFILE_PATH Dockerfile The path to the Dockerfile to be used for generating remediations. By default, the scanner looks for a file named Dockerfile in the root directory of the project, so this variable should only be configured if your Dockerfile is in a non-standard location, such as a subdirectory. See Solutions for vulnerabilities for more details.
KLAR_TRACE "false" Set to true to enable more verbose output from klar.
REGISTRY_INSECURE "false" Allow Klar to access insecure registries (HTTP only). Should only be set to true when testing the image locally.
SECURE_ANALYZERS_PREFIX "registry.gitlab.com/gitlab-org/security-products/analyzers" Set the Docker registry base address from which to download the analyzer.
SECURE_LOG_LEVEL info Set the minimum logging level. Messages of this logging level or higher are output. From highest to lowest severity, the logging levels are: fatal, error, warn, info, debug. Introduced in GitLab 13.1.

Overriding the container scanning template

If you want to override the job definition (for example, to change properties like variables), you must declare a container_scanning job after the template inclusion, and then specify any additional keys. For example:

include:
  - template: Container-Scanning.gitlab-ci.yml

container_scanning:
  variables:
    GIT_STRATEGY: fetch
Deprecated: GitLab 13.0 and later doesn’t support only and except. When overriding the template, you must use rules instead.

Vulnerability allowlisting

To allowlist specific vulnerabilities, follow these steps:

  1. Set GIT_STRATEGY: fetch in your .gitlab-ci.yml file by following the instructions in overriding the container scanning template.
  2. Define the allowlisted vulnerabilities in a YAML file named vulnerability-allowlist.yml. This must use the format described in the allowlist example file.
  3. Add the vulnerability-allowlist.yml file to your project’s Git repository.

Running container scanning in an offline environment

For self-managed GitLab instances in an environment with limited, restricted, or intermittent access to external resources through the internet, some adjustments are required for the container scanning job to successfully run. For more information, see Offline environments.

Requirements for offline container Scanning

To use container scanning in an offline environment, you need:

Note: GitLab Runner has a default pull policy of always, meaning the runner tries to pull Docker images from the GitLab container registry even if a local copy is available. The GitLab Runner pull_policy can be set to if-not-present in an offline environment if you prefer using only locally available Docker images. However, we recommend keeping the pull policy setting to always if not in an offline environment, as this enables the use of updated scanners in your CI/CD pipelines.

Make GitLab container scanning analyzer images available inside your Docker registry

For container scanning, import the following default images from registry.gitlab.com into your local Docker container registry:

registry.gitlab.com/gitlab-org/security-products/analyzers/klar
https://hub.docker.com/r/arminc/clair-db

The process for importing Docker images into a local offline Docker registry depends on your network security policy. Please consult your IT staff to find an accepted and approved process by which you can import or temporarily access external resources. Note that these scanners are updated periodically with new definitions, so consider if you are able to make periodic updates yourself.

For more information, see the specific steps on how to update an image with a pipeline.

For details on saving and transporting Docker images as a file, see Docker’s documentation on docker save, docker load, docker export, and docker import.

Set container scanning CI job variables to use local container scanner analyzers

  1. Override the container scanning template in your .gitlab-ci.yml file to refer to the Docker images hosted on your local Docker container registry:

    include:
      - template: Container-Scanning.gitlab-ci.yml
    
    container_scanning:
      image: $CI_REGISTRY/namespace/gitlab-klar-analyzer
      variables:
        CLAIR_DB_IMAGE: $CI_REGISTRY/namespace/clair-vulnerabilities-db
    
  2. If your local Docker container registry is running securely over HTTPS, but you’re using a self-signed certificate, then you must set DOCKER_INSECURE: "true" in the above container_scanning section of your .gitlab-ci.yml.

Automating container scanning vulnerability database updates with a pipeline

It can be worthwhile to set up a scheduled pipeline to build a new version of the vulnerabilities database on a preset schedule. Automating this with a pipeline means you won’t have to do it manually each time. You can use the following .gitlab-yml.ci as a template:

image: docker:stable

stages:
  - build

build_latest_vulnerabilities:
  stage: build
  services:
    - docker:19.03.12-dind
  script:
    - docker pull arminc/clair-db:latest
    - docker tag arminc/clair-db:latest $CI_REGISTRY/namespace/clair-vulnerabilities-db
    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
    - docker push $CI_REGISTRY/namespace/clair-vulnerabilities-db

The above template works for a GitLab Docker registry running on a local installation, however, if you’re using a non-GitLab Docker registry, you’ll need to change the $CI_REGISTRY value and the docker login credentials to match the details of your local registry.

Running the standalone container scanning tool

It’s possible to run the GitLab container scanning tool against a Docker container without needing to run it within the context of a CI job. To scan an image directly, follow these steps:

  1. Run Docker Desktop or Docker Machine.
  2. Run the latest prefilled vulnerabilities database Docker image:

    docker run -p 5432:5432 -d --name clair-db arminc/clair-db:latest
    
  3. Configure an environment variable to point to your local machine’s IP address (or insert your IP address instead of the LOCAL_MACHINE_IP_ADDRESS variable in the CLAIR_DB_CONNECTION_STRING in the next step):

    export LOCAL_MACHINE_IP_ADDRESS=your.local.ip.address
    
  4. Run the analyzer’s Docker image, passing the image and tag you want to analyze in the CI_APPLICATION_REPOSITORY and CI_APPLICATION_TAG environment variables:

    docker run \
      --interactive --rm \
      --volume "$PWD":/tmp/app \
      -e CI_PROJECT_DIR=/tmp/app \
      -e CLAIR_DB_CONNECTION_STRING="postgresql://postgres:password@${LOCAL_MACHINE_IP_ADDRESS}:5432/postgres?sslmode=disable&statement_timeout=60000" \
      -e CI_APPLICATION_REPOSITORY=registry.gitlab.com/gitlab-org/security-products/dast/webgoat-8.0@sha256 \
      -e CI_APPLICATION_TAG=bc09fe2e0721dfaeee79364115aeedf2174cce0947b9ae5fe7c33312ee019a4e \
      registry.gitlab.com/gitlab-org/security-products/analyzers/klar
    

The results are stored in gl-container-scanning-report.json.

Reports JSON format

The container scanning tool emits a JSON report file. For more information, see the schema for this report.

Here’s an example container scanning report:

{
  "version": "2.3",
  "vulnerabilities": [
    {
      "id": "ac0997ad-1006-4c81-81fb-ee2bbe6e78e3",
      "category": "container_scanning",
      "message": "CVE-2019-3462 in apt",
      "description": "Incorrect sanitation of the 302 redirect field in HTTP transport method of apt versions 1.4.8 and earlier can lead to content injection by a MITM attacker, potentially leading to remote code execution on the target machine.",
      "severity": "High",
      "confidence": "Unknown",
      "solution": "Upgrade apt from 1.4.8 to 1.4.9",
      "scanner": {
        "id": "klar",
        "name": "klar"
      },
      "location": {
        "dependency": {
          "package": {
            "name": "apt"
          },
          "version": "1.4.8"
        },
        "operating_system": "debian:9",
        "image": "registry.gitlab.com/gitlab-org/security-products/dast/webgoat-8.0@sha256:bc09fe2e0721dfaeee79364115aeedf2174cce0947b9ae5fe7c33312ee019a4e"
      },
      "identifiers": [
        {
          "type": "cve",
          "name": "CVE-2019-3462",
          "value": "CVE-2019-3462",
          "url": "https://security-tracker.debian.org/tracker/CVE-2019-3462"
        }
      ],
      "links": [
        {
          "url": "https://security-tracker.debian.org/tracker/CVE-2019-3462"
        }
      ]
    }
  ],
  "remediations": [
    {
      "fixes": [
        {
          "id": "c0997ad-1006-4c81-81fb-ee2bbe6e78e3"
        }
      ],
      "summary": "Upgrade apt from 1.4.8 to 1.4.9",
      "diff": "YXB0LWdldCB1cGRhdGUgJiYgYXB0LWdldCB1cGdyYWRlIC15IGFwdA=="
    }
  ]
}

Security Dashboard

The Security Dashboard shows you an overview of all the security vulnerabilities in your groups, projects and pipelines.

Vulnerabilities database update

For more information about the vulnerabilities database update, check the maintenance table.

Interacting with the vulnerabilities

After a vulnerability is found, you can interact with it.

Solutions for vulnerabilities (auto-remediation)

Some vulnerabilities can be fixed by applying the solution that GitLab automatically generates.

To enable remediation support, the scanning tool must have access to the Dockerfile specified by the DOCKERFILE_PATH environment variable. To ensure that the scanning tool has access to this file, it’s necessary to set GIT_STRATEGY: fetch in your .gitlab-ci.yml file by following the instructions described in this document’s overriding the container scanning template section.

Read more about the solutions for vulnerabilities.

Troubleshooting

docker: Error response from daemon: failed to copy xattrs

When the runner uses the docker executor and NFS is used (for example, /var/lib/docker is on an NFS mount), container scanning might fail with an error like the following:

docker: Error response from daemon: failed to copy xattrs: failed to set xattr "security.selinux" on /path/to/file: operation not supported.

This is a result of a bug in Docker which is now fixed. To prevent the error, ensure the Docker version that the runner is using is 18.09.03 or higher. For more information, see issue #10241.

Getting warning message gl-container-scanning-report.json: no matching files

For information on this, see the general Application Security troubleshooting section.