Container Scanning: How It Works, Implementation & Best Practices

Container scanning entails analyzing containers—lightweight units that package an application's code, dependencies, and runtime environment.

July 26, 2023

What Is Container Scanning? 

Container scanning entails analyzing containers—lightweight units that package an application’s code, dependencies, and runtime environment. The primary goal of container scanning is to identify vulnerabilities within these components and ensure their security before deployment.

To prevent cyber threats in your development pipeline, organizations implement container scanning practices including:

  • Vulnerability detection: Container scanning detects known vulnerabilities in your application’s code or its dependencies by comparing them against vulnerability databases, such as the National Vulnerability Database (NVD).
  • Compliance checks: Container scanners can verify if your application adheres to specific compliance standards or security benchmarks, by checking configurations and settings within the container image.
  • Misconfiguration detection: Misconfigurations can lead to potential security risks, so identifying them early through container scans minimizes the chances of exploitation during runtime.

This is part of a series of articles about application security.

In this article:

How Does Container Scanning Work? 

Container scanning is a process that involves three main steps:

Analyzing Base Images

The first step in container scanning is to analyze the base image on which your containers are built. These images often contain pre-installed software packages and libraries that can introduce vulnerabilities if not properly maintained. A good practice is to use minimal base images from trusted sources. For example, Alpine Linux is a Linux distribution that reduces the attack surface by including only essential components.

Scanning Dependencies

Besides examining the base image, scanning your application’s dependencies for known vulnerabilities is crucial. This includes third-party libraries or frameworks used in your project. Tools like OWASP Dependency-Check can help automate this process by checking against vulnerability databases, such as the National Vulnerability Database (NVD).

Evaluating Application Code

Beyond external components, assessing your application code for potential issues, such as insecure coding practices or misconfigurations, is essential. Static analysis tools can automatically review your source code for common security flaws, while dynamic analysis tools, such as penetration testing suites, provide insights into runtime behavior.

Key Areas to Implement Container Scanning 

There are two key areas for implementing container scanning: in your container registry and at runtime.

Scanning Your Container Registry

Your container registry stores all the images used for your applications and projects, making it a vital component of your infrastructure. Regularly scanning these images can help identify vulnerabilities before they become an issue in production. To do this, you can use open source tools like Trivy, which scan each image against known vulnerability databases and provide detailed reports on any issues found.

Scanning Your Container at Runtime

In addition to scanning registries, monitoring containers during runtime for potential threats or anomalies is important. This involves continuously analyzing running the behavior of containers to detect suspicious activities that may indicate a security breach or compromise. 

Runtime container security tools allow you to: 

  • Receive alerts: Provide real-time alerts on container security issues based on predefined rulesets.
  • Create policies: Define custom policies tailored to your specific environment requirements and application needs.
  • Maintain visibility: Monitor all aspects of container activity to ensure you have a clear understanding of your application’s security posture.
  • Automate response: Integrate container scanning with other security tools and your CI/CD pipeline, to automate the process of vulnerability remediation, and reduce the risk of human error.

Key Findings of a Container Scan 

A container scan is an analysis of a container image to identify any security vulnerabilities, misconfigurations, or compliance issues. Here are some key findings that you might obtain from a container scan:

Vulnerabilities in the Image

One of the most common findings from a container scan is the presence of vulnerabilities in the image. These might be in the form of outdated or insecure libraries, insecure versions of languages or frameworks, or insecure system packages. The scan report typically includes information about the severity of the vulnerabilities, their Common Vulnerabilities and Exposures (CVE) identifiers, and possible remediation steps.

Insecure Configurations

A container scan can also identify insecure configurations that could be exploited by an attacker. For example, it might flag containers that are running as root, which could present a security risk. Other insecure configurations might include open network ports, unnecessary privileges, or insecure communication protocols.

Compliance Issues

Container scans can also check for compliance with security best practices or specific security standards or benchmarks. This might involve checks for things like the use of secure base images, proper handling of sensitive data, or appropriate logging and monitoring. The scan can identify areas where the container does not meet the necessary compliance requirements.

Software Inventory

A container scan can provide a detailed inventory of the software components included in the image, such as operating system packages, libraries, and application components. This inventory can be useful for managing dependencies and for understanding the potential attack surface of the container.

Learn more in our detailed guide to vulnerability scanning

Types of Container Scanning Tools 

Dedicated Container Scanning Tools

There are several open source container scanning tools available, which offer a cost-effective approach to detecting container vulnerabilities. However, they might lack some advanced features. Commercial solutions provide extensive vulnerability management and enterprise features, as well as support and specialized security research teams. Some tools are part of a more comprehensive Cloud Native Application Protection Platform (CNAPP).

Cloud Provider-Native Tools

Several cloud providers, including Amazon Web Services (AWS), Google Cloud Platform (GCP), and Microsoft Azure, offer their own container scanning tools. Examples include Amazon ECR Image Scanning, Google Container Registry Vulnerability Scanning, and Azure Security Center. By utilizing these native solutions, you can easily integrate vulnerability management with your existing cloud infrastructure.

Add-Ons for Container Orchestrators

Container orchestration platforms like Kubernetes support integrated container scanning through third-party plugins or extensions. These integrations enable developers to automate vulnerability scans directly within their deployment pipelines, ensuring continuous security monitoring throughout the application lifecycle.

Best Practices for Container Image Scanning 

To effectively leverage container scanning for securing your containerized applications, follow these best practices:

  • Integrate scanning into the CI/CD pipeline: Incorporate container scanning into your continuous integration and continuous delivery (CI/CD) pipeline to identify and fix security issues early in the development process. This helps prevent vulnerabilities from reaching production environments.
  • Regularly update base images: Many container images are built on top of base images, which include the operating system and other dependencies. Ensure that you regularly update the base images to their latest stable and secure versions to minimize the risk of using outdated components with known vulnerabilities.
  • Use minimal base images: Use minimal or lightweight base images that only include essential components required for your application. This reduces the attack surface by limiting the number of potential vulnerabilities in the image.
  • Scan for vulnerabilities and misconfigurations: Ensure that your container scanning tool checks for both known vulnerabilities in the software components and common misconfigurations, such as insecure settings or exposed secrets.
  • Prioritize and remediate: Use the severity ratings and potential impact of the identified issues to prioritize which vulnerabilities and misconfigurations need to be addressed first. Implement the necessary fixes, such as patching or updating affected components, and then re-scan the container images to confirm that the issues have been resolved.
  • Automate and enforce policies: Automate the container scanning process and enforce policies that require container images to pass security checks before they can be deployed. This helps ensure that only secure images are deployed in production environments.
  • Monitor for new vulnerabilities: Continuously monitor vulnerability databases and security advisories to stay informed about new threats and vulnerabilities that may affect your container images. Update your scanning tools and processes accordingly to identify and address these emerging threats.
  • Implement runtime security: Container scanning helps identify issues in container images, but it is also essential to monitor and protect containers during runtime. Implement runtime security measures, such as intrusion detection and prevention systems (IDPS), to detect and respond to potential threats in real-time.

By following these best practices, organizations can maximize the benefits of container scanning to enhance the security of their containerized applications and reduce the risk of security breaches and exploits.

Container Scanning with Aqua Security

Aqua Cloud Workload Protection (CWPP) is powerful, comprehensive protection for applications that are running cloud native workload such as containers, virtual machines, serverless functions, and Kubernetes (K8s) and Platform-as-a-Service (PaaS) environments.

Aqua’s CWPP solution includes several predefined container runtime policies that are supported by the Aqua Enforcer suiter. Container drift prevention is a predefined runtime policy that detects the running of executables not in the original image and automatically blocks any lateral movement or escalation within or between your cloud workloads. This patented technology ensures you can harden your environment and stop zero-day attacks.