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Dexter

Don't expect your engineers to know why or how they should declare their image references for better security, leave it to Dexter.

dexter project logo (imported from https://github.com/ashleymcnamara/gophers)

What does Dexter Do?

Dexter can be placed into your CI processes to scrape through the repository and find files that contain image references, with the aim of pinning them to the immutable digest.

What can Dexter Find?

Dexter currently has a small selection of parsers that are able to find image references within the file types they are designed to assess. These are:

  • Kubernetes (currently supports Pod, Deployment, Replicaset, Statefulset, Daemonset, Job, CronJob)
  • Dockerfile

What Problem does this solve?

Let's say I have a file with an image declared like so:

image: 'grafana/grafana:4.2.0'

The 4.2.0 is what is called an image tag. Image tags (as you might have guessed), make it quick and easy to point to an image, but it is not an immutable identity to an image itself. The tag points to a long (not very nice to look at) sha256 hash known as an image digest:

7ff7f9b2501a5d55b55ce3f58d21771b1c5af1f2a4ab7dbf11bef7142aae7033

Image digests are great because they are the immutable identity that an image tag points to. But why do I care? A-ha! This is where Dexter comes in.

the 4.2.0 tag points to the 7ff7f9b2501a5d55b55ce3f58d21771b1c5af1f2a4ab7dbf11bef7142aae7033 digest identity of the image sat in the registry. However, nothing is stopping me as someone with write access to the registry, to point the 4.2.0 tag at a different image. In most cases this could be innocent changes to the image, but to do such a thing is never good practice. In the worst case, this could be a malicious modification to the image so it contains a cypto-miner, or in other words; a supply-chain attack.

Once you have applied Dexter against your repository, your image reference (taking the grafana image shown above as an example) will look like:

image: index.docker.io/grafana/grafana@sha256:7ff7f9b2501a5d55b55ce3f58d21771b1c5af1f2a4ab7dbf11bef7142aae7033

Now if this image is running in your estate, you will not be susceptible to an image tag getting hijacked and you will no longer get hit by the dreaded crypto-miner under this use case! woohoo!

Quickstart

To quickly test out the tool on your repository, simply execute the following command from within the Dexter repository:

go run . manipulate --directory <your-repository-directory>

Dexter Configuration

Dexter has a simple configuration file for allowing you to specify how you would like it to behave when it executes against your repository. Please note that this is currently very basic, and there is an intention to make this more fully featured in the near future.

Parsers

This allows you to select the parsers that you wish to use:

parsers:
- "dockerfile"
- "kubernetes"

Of course there are not many parsers yet 👀 but hopefully this will become handy in the near future.

Ignore

If you have specific files or even references that exist within the path you are scanning that you do not want to touch, Dexter will ensure that they are left alone to the letter. Just ensure that you add them to the ignore field inside the Dexter configuration file:

ignore:
   files:
   - cmd/root.go
   - test.yaml
   references:
   - grafana/grafana:latest

Feel free to give it a try!