Klar : Integration Of Clair And Docker Registry

Klar is a simple tool to analyze images stored in a private or public Docker registry for security vulnerabilities using Clair https://github.com/coreos/clair. It is designed to be used as an integration tool so it relies on environment variables. It’s a single binary which requires no dependencies.

It serves as a client which coordinates the image checks between the Docker registry and Clair.

Binary Installation

The simplest way is to download the latest release (for OSX and Linux) from https://github.com/optiopay/klar/releases/ and put the binary in a folder in your PATH (make sure it has execute permission).

Installation From Source Code

Make sure you have Go language compiler installed and configured https://golang.org/doc/install

Then run

go get github.com/optiopay/klar

make sure your Go binary folder is in your PATH (e.g. export PATH=$PATH:/usr/local/go/bin)


Klar process returns if 0 if the number of detected high severity vulnerabilities in an image is less than or equal to a threshold (see below) and 1 if there were more. It will return 2 if an error has prevented the image from being analyzed.

Klar can be configured via the following environment variables:

  • CLAIR_ADDR – address of Clair server. It has a form of protocol://host:portprotocol and port default to http and 6060 respectively and may be omitted. You can also specify basic authentication in the URL: protocol://login:password@host:port.
  • CLAIR_OUTPUT – severity level threshold, vulnerabilities with severity level higher than or equal to this threshold will be outputted. Supported levels are Unknown, Negligible, Low, Medium, High, Critical, Defcon1. Default is Unknown.
  • CLAIR_THRESHOLD – how many outputted vulnerabilities Klar can tolerate before returning 1. Default is 0.
  • CLAIR_TIMEOUT – timeout in minutes before Klar cancels the image scanning. Default is 1
  • DOCKER_USER – Docker registry account name.
  • DOCKER_PASSWORD – Docker registry account password.
  • DOCKER_TOKEN – Docker registry account token. (Can be used in place of DOCKER_USER and DOCKER_PASSWORD)
  • DOCKER_INSECURE – Allow Klar to access registries with bad SSL certificates. Default is false. Clair will need to be booted with -insecure-tls for this to work.
  • DOCKER_TIMEOUT – timeout in minutes when trying to fetch layers from a docker registry
  • DOCKER_PLATFORM_OS – The operating system of the Docker image. Default is linux. This only needs to be set if the image specified references a Docker ManifestList instead of a usual manifest.
  • DOCKER_PLATFORM_ARCH – The architecture the Docker image is optimized for. Default is amd64. This only needs to be set if the image specified references a Docker ManifestList instead of a usual manifest.
  • REGISTRY_INSECURE – Allow Klar to access insecure registries (HTTP only). Default is false.
  • JSON_OUTPUT – Output JSON, not plain text. Default is false.
  • FORMAT_OUTPUT – Output format of the vulnerabilities. Supported formats are standard, json, table. Default is standard. If JSON_OUTPUT is set to true, this option is ignored.
  • WHITELIST_FILE – Path to the YAML file with the CVE whitelist. Look at whitelist-example.yaml for the file format.
  • IGNORE_UNFIXED – Do not count vulnerabilities without a fix towards the threshold

Also Read – ROADTools : The Azure AD Exploration Framework


CLAIR_ADDR=localhost CLAIR_OUTPUT=High CLAIR_THRESHOLD=10 DOCKER_USER=docker DOCKER_PASSWORD=secret klar postgres:9.5.1

Debug Output

You can enable more verbose output but setting KLAR_TRACE to true.

  • run export KLAR_TRACE=true to persist between runs.

Dockerized Version

Klar can be dockerized. Go to $GOPATH/src/github.com/optiopay/klar and build Klar in project root. If you are on Linux:

CGO_ENABLED=0 go build -a -installsuffix cgo .

If you are on Mac don’t forget to build it for Linux:

GOOS=linux go build .

To build Docker image run in the project root (replace klar with fully qualified name if you like):

docker build -t klar .

Then pass env vars as separate --env arguments, or create an env file and pass it as --env-file argument. For example save env vars as my-klar.env:


Then run

docker run –env-file=my-klar.env klar postgres:9.5.1

Amazon ECR Support

There is no permanent username/password for Amazon ECR, the credentials must be retrived using aws ecr get-login and they are valid for 12 hours. Here is a sample script which may be used to provide Klar with ECR credentials:

DOCKER_LOGIN=`aws ecr get-login –no-include-email`
PASSWORD=`echo $DOCKER_LOGIN | cut -d’ ‘ -f6`
REGISTRY=`echo $DOCKER_LOGIN | cut -d’ ‘ -f7 | sed “s/https:\/\///”` DOCKER_USER=AWS DOCKER_PASSWORD=${PASSWORD} ./klar ${REGISTRY}/my-image

Google GCR Support

For authentication against GCR (Google Cloud Registry), the easiest way is to use the application default credentials. These only work when running Klar from GCP. The only requirement is the Google Cloud SDK.

DOCKER_PASSWORD=“$(gcloud auth application-default print-access-token)”

With Docker:

DOCKER_PASSWORD=“$(docker run –rm google/cloud-sdk:alpine gcloud auth application-default print-access-token)”