Continuous Security with Jenkins and Docker Bench

Docker Bench
Image by Docker Inc. ©

Docker Bench is an open source tool for automatically validating the configuration of a host running Docker containers. The tool has been written among others by Diogo Mónica, security lead at Docker, and performs security checks at the container level following Docker’s CIS Benchmark recommendations.

As you would expect, the easiest way to run Docker Bench is via a Docker container. Just make sure you have Docker 1.10 or better, download the Docker image:

and run the Docker container as follows:

This will automatically generate some output as in the animated gif above with an assessment of possible Docker security issues.

I recently combined Docker Bench with Jenkins in order to integrate security testing into a typical DevOps workflow on the cloud – call it DevSecOps if you like buzzwords… This requires a little bit of Jenkins configuration but it’s not too difficult to follow.

The first thing to do is to make sure that openssh is installed on the instance where Jenkins is running and on the host you want to check. For example on Ubuntu you can install openssh with:

Then install the SSH Agent plugin in Jenkins. This will provide Jenkins with SSH credentials to automatically login into a machine on the cloud. Add the credentials in Jenkins -> Credentials -> System -> Global credentials (unrestricted) -> Add credentials -> SSH Username with private key.  This is an example of my credentials for user jenkins (private key details are obfuscated):

set up mock SSH credentialsThen create a Jenkins job and select the SSH agent credentials for user jenkins in Build Environment:

SSH agent credentialsThis will allow Jenkins to SSH into the machine with the private key stored securely (make sure you only grant permission to configure Jenkins to administrators otherwise your private keys are not safe).

I like to parameterize my builds so that I can run Docker Bench on any host reachable with the private key:

parameterize build with hostnameFinally, select Execute shell in the build and paste this shell script (you may want to put it under version control and retrieve it from there via Jenkins):

It works likes this:

  • the first command allows Jenkins to ssh into a host (I’m using AWS EC2 as you can guess by the username ec2-user, replace it with your default username but do not user root). Note that the environment variable $HOSTNAME is passed from the parameter we set up earlier. The EOF allows to run a sequence of commands directly on the host so that you don’t have to disconnect every time. The single quotes are important, don’t skip them!
  • the second command pulls the Docker image for Docker Bench directly on the host
  • the third command runs Docker Bench on the host
  • the forth command removes all exited containers from the host, including Docker Bench once it has finished its job
  • the fifth command remove the Docker image for Docker Bench so that you don’t leave any trace on the host
  • the final EOF disconnect Jenkins from host

The Jenkins console output shows the result of running Docker Bench on a specific host. Now you have to assess the results as you may see several warnings and they may just be false positives. For example, this warning may be acceptable for you:

This means you are not running the latest version of Docker. This may not be an issue (unless Docker released a security release) especially if your Linux distribution hasn’t got the latest version of Docker available in its repositories.

In my case this warning was a false positive:

In fact, I need several containers to communicate between them so that restriction does not apply to my use case.

This warning should be taken much more seriously:

This means you are running a container as root. This is unsecure as if a nasty intruder manages to get inside the containers s/he can run any command in it. Basically, it’s like running a Linux system as root which is a bad security practice.

Once you have assessed your warnings, you may want to filter out the false positives. For example, you can use the Post build task plugin to make the build fail if the build log output contains a warning that you assessed as a security risk. You can use a regular expression to match the pattern identified above.

It would be good to get the Docker Bench output in JUnit format so that Jenkins can understand it natively but this option is currently not implemented in Docker Bench.

Happy security testing with Jenkins and Docker Bench!

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