Home Did you know ? What is a Docker image scan and how does it improve container image security

What is a Docker image scan and how does it improve container image security

by Mic Johnson

Docker is popular across the world with over 10 million users. The platform has transformed the way applications are developed. With increased development because of containerization, extra security duties are going to developers.

Today, developers have to maintain container images beside their code. That is why Docker image security scanning needs to be at the center of your Docker security strategy.

Please mind that image scanning will not protect you from all security vulnerabilities, but it is the primary defense against insecure code in container images. Thus, it is the foundation of Docker security.

What is a Docker image scan?

It is the process of finding security vulnerabilities in your Docker image files. Usually, it functions by parsing through packages or other dependencies defined in your Docker container image file.

It is then followed by checking if there are known vulnerabilities in those dependencies and packages. This gives you an opportunity to find and fix vulnerabilities before pushing the image to the Docker hub.

You need a special tool like Docker Hub with built-in scanners to scan Docker images. Besides, you can also opt for other image and registry scanners all with varying degrees of user experience and functions.

Importance of Docker image scanning

Typically, image scanning checks layers in images if they contain any vulnerabilities then notifies builders about the issues. This way, developers can update docker images to eradicate detected threats.

Container security helps make the entire imaging scanning seamless by allowing you to develop security policies from scan results. It ensures only safe images that meet preset security criteria are used.

Automated image scanning with the best practices

How to improve container image security

  1. Integrate image scanning in your pipeline

As you build container images, you need to be extra careful by scanning them before publishing them. Leverage the container image pipelines you have in place for your workflow and add one step to carry out image scanning.

Once the code is built and tested, you push the images to a staging repository instead of a production repository. You can now do your image scanning. Depending on the tool you use, you will get a report listing various issues found and assigning each severity level.

Automation is important. It allows you to catch vulnerabilities before entering your registry. Thus, it stops issues reaching the production stage of your application development.

  1. Embrace inline scanning

You can adopt inline scanning avoiding the need to go through the staging repository. It allows you to scan images directly from your container image pipeline.

Inline image scanning only transmits the scan metadata to your scanning tool. The approach helps you retain control over privacy.

  1. Scan for OS vulnerabilities

The best approach to ensuring container security is by keeping in mind that the lighter the image the better. It translates into faster scans, faster builds, and fewer dependencies and vulnerabilities.

  1. Scan images during development

Rebuilding an image or creating an image from a Dockerfile can introduce vulnerabilities in the system. You should include Docker image scanning as part of the workflow during development to capture vulnerabilities early on.

It occurs at all stages of the development cycle. So, you should consider automating the process of Docker image scanning.

  1. Scan images during production

It is recommended that you actively check your container. This saves you plenty of time after a vulnerability is established which would otherwise threaten your production system.

Periodically scanning Docker images helps you monitor the capabilities of containers. The process creates a snapshot of image dependencies that help in continuous monitoring.

Also, you need to activate runtime monitoring. Looking for unused packages and modules during runtime provides you insight into the way you can shrink Docker images. Getting rid of unused components helps prevent unnecessary vulnerabilities from accessing application libraries and the system.

Build-time scanning does not eliminate the need for runtime scanning. On the contrary, it is more important for your image and any third-party image you want to use.

  1. Put in place control measures

Embrace organization-wide policy surrounding the acquisition and use of container images. With policies, you can govern areas such as version control, approved registries, and more.

  1. Use signatures

Another way of ensuring container image security is through image signing and verification. It gives developers the ability to establish if the image originates from a trusted source and has not been modified.

The container ecosystem places a premium on the trust factor. Various container platforms embrace different approaches to image signing. However, they are based on digital signatures.

In case malicious attackers access your running container, ensure they have as few tools as possible to exploit. A minimal base image provides a great starting point.

Why do container image scanning

Since containers are created from images downloaded from remote resources, it is important to have routine inspections of every image. You can never be sure about the security of third-party code.

The best way is to scan each image for possible security issues. Also, it is advisable that you use a tool with a reputation of having an up-to-date vulnerability database.

It is best to scan all image layers as early as possible. This means you should scan images from public registries once you download them. Another benefit of image scanning is it helps inform the software bill of materials. Traditionally, it has been a problem for container users.

Unsafe images should never find their way to your production-accessible container registry. Scanning an image across its lifecycle is essential. Besides, you need to develop mechanisms for dealing with image security.


Today, containers are the industry standard for packaging, deploying, and running software. The approach is helping change application deployment, scalability, and portability. However, they pose potential vulnerabilities.

Securing container images is a continuous process. It incorporates the best practices to plan and build efficient and secure Docker images. One approach is through the use of image scanning to help establish vulnerabilities in container images.

You may also like