Containers have fundamentally changed how we build, ship, and run applications. They offer portability, consistency, and scalability, making them a cornerstone of modern software development and DevOps practices. However, this convenience comes with a new set of security responsibilities. A container image is not just your application code; it’s a layered filesystem that includes a base operating system, system libraries, application dependencies, and your custom code. A vulnerability in any of these layers can put your entire application at risk.
This is why container image scanning is a critical security practice. It involves analyzing the contents of a container image to identify known security vulnerabilities. But manual scanning is not enough. To keep pace with rapid development cycles, you must automate this process within your Continuous Integration/Continuous Deployment (CI/CD) workflow. This ensures that every image is vetted for security flaws before it ever gets deployed.
The High Stakes of Container Vulnerabilities
Container images are often built upon public base images from sources like Docker Hub. While convenient, these base images can contain outdated packages with known vulnerabilities. A study found that many official images on Docker Hub contained critical security flaws. If you unknowingly build your application on a compromised foundation, you are inheriting all of its security risks.
For a comprehensive overview of recent threats, read the CNCF Cloud Native Security Whitepaper. To explore real-world examples and statistics about container vulnerabilities, see Red Hat’s State of Kubernetes Security Report.
Common vulnerabilities found in container images include:
- Outdated OS Packages: Flaws in core operating system components like glibc or openssl can lead to remote code execution or other severe compromises.
- Vulnerable Application Dependencies: Your application relies on open-source libraries. A flaw in one of these dependencies (e.g., Log4Shell) can be packaged into your image, creating a massive security hole.
- Insecure Configurations: The image might be configured to run as a root user by default, or it could contain hardcoded secrets like API keys or passwords, which can be easily extracted.
Failing to address these issues can lead to data breaches, service disruptions, and non-compliance with regulatory standards. Manually tracking vulnerabilities across hundreds of images and their dependencies is an impossible task. Automation is the only viable solution.
Integrating Container Scanning into Your CI/CD Workflow
The CI/CD pipeline is the perfect place to automate security checks. By integrating container scanning here, you “shift left,” catching vulnerabilities early in the development process when they are easiest and cheapest to fix. This prevents insecure images from being pushed to your container registry or deployed to production environments like Kubernetes.
For a clear overview of best practices, the National Institute of Standards and Technology (NIST) provides important guidelines for securing containers within DevSecOps pipelines. Likewise, OWASP’s Cheat Sheet on CI/CD Security offers actionable advice for integrating security at every step of your build process.
Here are the actionable steps to automate container image scanning:
Step 1: Choose the Right Scanning Tool
Select a container scanning tool that fits your needs. Popular open-source options like Trivy and Grype are excellent choices, known for their speed and comprehensive vulnerability databases. Commercial platforms often provide more advanced features, such as policy enforcement and integration with broader security ecosystems. Your tool should be able to scan for both OS package vulnerabilities and application-level dependencies (Software Bill of Materials or SBOM).
Step 2: Add a Scanning Stage to Your Pipeline
Modify your CI/CD configuration file (e.g., .gitlab-ci.yml, Jenkinsfile, or GitHub Actions workflow) to add a new stage for security scanning. This stage should occur right after the container image is built but before it is pushed to a container registry.
A typical pipeline might look like this:
- Build: Compile the application code.
- Test: Run unit and integration tests.
- Build Image: Create the Docker image.
- Scan Image:(New Stage) Run the container scanner on the newly built image.
- Push to Registry: If the scan passes, push the image to your registry (e.g., Docker Hub, ECR, GCR).
- Deploy: Deploy the image to a staging or production environment.
Step 3: Configure the Scan and Set Failure Policies
Configure the scanner to fail the CI/CD build if critical or high-severity vulnerabilities are detected. This is a crucial step. Without a failure policy, the scan is just an informational step that can be easily ignored. By failing the build, you create a “security gate” that prevents vulnerable code from progressing.
Your configuration might look something like this in a CI script:
trivy image –exit-code 1 –severity HIGH,CRITICAL your-app-image:latest
This command tells the Trivy scanner to exit with a non-zero code (which fails the CI job) if any HIGH or CRITICAL severity vulnerabilities are found.
Step 4: Provide Actionable Feedback to Developers
When a scan fails, it is essential to provide clear, actionable feedback to the developer. The CI/CD job logs should show which vulnerabilities were found, which packages are affected, and ideally, which version contains a fix. Good tooling makes this process simple. For example, the output might say, “Vulnerability CVE-2023-1234 found in openssl version 1.1.1g. Upgrade to 1.1.1k.” This allows the developer to quickly update their Dockerfile, rebuild the image, and get a green build.
Simplifying the Process with a Unified Platform
Managing multiple security tools for different parts of your stack can lead to complexity and alert fatigue. This is where a unified platform like Aikido Security offers a significant advantage. Aikido integrates with best-in-class open-source scanners, including for containers, and brings all the findings into a single, easy-to-use dashboard.
Instead of wrestling with different tools and formats, your team gets a consolidated view of all vulnerabilities—from source code (SAST) and dependencies (SCA) to container images and cloud configurations. Aikido intelligently prioritizes findings, filtering out the noise so developers can focus on the most critical risks. It integrates seamlessly into your Git workflow, providing feedback directly in pull requests and making security a natural part of the development process.
Build Security into Every Layer
Containers provide immense benefits for agility and scalability, but they require a new approach to security. By automating container image scanning within your CI/CD workflow, you can ensure that every image you deploy has been vetted for known vulnerabilities. This practice transforms security from a reactive, manual task into a proactive, automated part of your development lifecycle. It empowers your developers to build and ship code quickly and confidently, knowing that security is built-in from the start.