Neglecting Container Scanning? Prepare for a Breach!

What Are Containers?

Containers are lightweight, isolated Linux processes that run within the framework of namespaces and cgroups. These processes operate in their own confined environments, allowing specific resources like networking and filesystems to be segregated. The term container aptly captures the concept of encapsulating these isolated processes.

Low-level container runtimes handle their creation and management. They initiate processes, establish cgroups, assign processes to unique namespaces via the unshare system call, and perform necessary clean-up once the container exits.

A common tool for creating, building, and running containers is Docker, which uses a configuration file called a Dockerfile. This file outlines a series of instructions to define the container's behavior during the image-building process.

What Is Container Scanning?

When working with containers, security risks can arise from various sources, such as vulnerabilities in the base image, third-party dependencies, or the code itself. Container scanning addresses these risks by evaluating the container’s layers and identifying issues that need fixing.

This process involves analyzing the container image to detect vulnerabilities, configuration flaws, or outdated dependencies. Scanning results offer insights into potential security threats and provide recommendations for remediation. Additionally, they help ensure the container is compliant with organizational policies and standards before deployment.

Let’s delve deeper into container layers and the scanning techniques used to ensure their security.

Image Layers and How to Scan Them

1. Code Scanning (SAST & Dependency Analysis)
   A thorough scan of first- and third-party code identifies vulnerable dependencies. For instance, adding an outdated Java library could expose your container to security exploits. Using tools for Static Application Security Testing (SAST) and Software Composition Analysis (SCA), you can uncover such issues and apply remediations effectively.

2. Configuration Scanning
   Configuration scans examine the Dockerfile or container for issues like running as the root user or storing plaintext secrets. By detecting these flaws, you can improve security and ensure compliance with policy checks before deployment.

3. Base Image Vulnerability Scanning
   Containers often rely on base images like Alpine or Ubuntu, which may contain known vulnerabilities (identified by CVEs). Scanning these base layers helps prioritize fixes by assessing the severity and risk of each vulnerability, using metrics like the CVSS score.

Where Should Containers Be Scanned?

1. Integrated Development Environment (IDE)
   Scanning begins in the IDE, where developers can analyze both application code and Dockerfiles. Tools integrated into the IDE streamline fixes, enabling issues to be resolved before building the container.

2. Build Stage
   Containers can be built locally with Docker or within a CI/CD pipeline. A pipeline approach applies automated policies that block non-compliant images from being pushed to registries, ensuring only secure builds progress.

3. Container Registry
   Registries like AWS Elastic Container Registry (ECR) periodically scan stored images for vulnerabilities. This ensures that as new vulnerabilities emerge, actionable insights are provided, enabling developers to address them promptly.

4. Runtime Environments
   Cloud Native Application Protection Platforms (CNAPPs) offer runtime scanning capabilities. They provide visibility into containers running in Kubernetes clusters, enabling security teams to assess real-time risks and calculate business impact.

Image Lifecycle Management

A robust container lifecycle management process ensures ongoing security. During the build pipeline:

• If an image passes security scans, it moves to the container registry.

• If it fails, the pipeline halts, and alerts are sent to the team via tools like Slack or Jira. Developers can then update the Dockerfile, rebuild the image, and retry until the checks are passed.

Lifecycle management not only reduces vulnerabilities but also fosters a culture of proactive security.

Scanning Tools

Container scanning tools fall into three main categories:

1. Open-Source Tools
   Popular tools include Trivy, Docker Scout, and Snyk (free tier). These tools enable efficient scanning to identify security flaws in container images.

2. Cloud-Native Tools
   AWS’s ECR integrated with AWS Inspector offers advanced scanning capabilities for an additional cost. This service can suffice for many organizations without requiring third-party tools.

3. Commercial Tools
   Paid tools like Wiz provide comprehensive features, including deep visibility into containers, Kubernetes, and cloud platforms. They combine scanning functionalities across different SDLC stages to offer a complete risk overview.

Hands-On Container Scanning

Docker Desktop’s Docker Scout

Docker Scout, integrated into Docker Desktop, visually displays vulnerabilities layer by layer within your image. It highlights fixes and provides a graphical overview of risks.

Installing and Using Trivy

For a command-line alternative to Docker Scout, Trivy is a powerful scanner. Below are installation instructions for Ubuntu systems:

sudo apt-get install wget apt-transport-https gnupg
wget -qO - https://aquasecurity.github.io/trivy-repo/deb/public.key | gpg --dearmor | sudo tee /usr/share/keyrings/trivy.gpg > /dev/null
echo "deb [signed-by=/usr/share/keyrings/trivy.gpg] https://aquasecurity.github.io/trivy-repo/deb generic main" | sudo tee -a /etc/apt/sources.list.d/trivy.list
sudo apt-get update
sudo apt-get install trivy

To scan an image, use:

trivy image redis

This command analyzes the Redis image, listing detected vulnerabilities and providing remediation advice.

Trivy Configuration Scan

Trivy can also scan for configuration issues, such as missing a USER command, which indicates that a container might run as the root user.

Snyk Code Scanning

With the Snyk plugin for Visual Studio Code, developers can scan their code directly within the IDE. It highlights vulnerabilities and provides fixes, streamlining the remediation process.

Why Regular Container Scanning Matters

Cyberattacks are on the rise, and businesses must prioritize container security to mitigate risks like privilege escalation or persistent threats. Routine scanning allows teams to identify and resolve vulnerabilities before they become exploitable.

Failing to scan regularly exposes the business to potential breaches, leading to costly downtime, reputation damage, and resource drain. Proactive scanning equips developers with tools and guidance to secure containers throughout their lifecycle.

Recommendations for Securing Containers

1. Review and Enforce Security Policies
   Create clear container security policies and implement them as Policy-As-Code using tools like Open Policy Agent. Regularly review these policies to stay aligned with evolving standards.

2. Rebuild Containers Regularly
   Frequently updating container images ensures timely fixes for critical vulnerabilities, reducing the likelihood of security incidents.

3. Expire Old Images
   Keep only recent images in your registry. Retain older versions in Git to prevent clutter and minimize vulnerability management overhead.

4. Curate Base Images
   Use minimal base images, such as distroless or scratch, to reduce the attack surface. Consistently update base images to simplify maintenance.

Final Thoughts

Container scanning is an integral part of any vulnerability management program, especially when Kubernetes is a core compute platform. By shifting security left—addressing issues early in the SDLC—you minimize long-term technical debt and reduce the risk of post-deployment vulnerabilities.

Empower your development teams with user-friendly tools like Snyk and Wiz to detect, understand, and resolve issues efficiently. This approach fosters a culture of security while ensuring smooth and secure application deployments.