What is Container Image Security?

As containerization grows, so do security concerns. Our 2024 guide on container image security offers best practices and tips to ensure your container images remain secure and resilient against attacks.

According to Forrester, 71% of DevOps teams use containers and microservices to deliver applications. Containers are light and modular, so you can update a service without worrying that it will mess up another part of the system.

However, containerization comes with its own set of challenges. For instance, we need to tackle issues related to container image security.

Every container image contains metadata describing the containers’ environmental context and hardware, such as configuration details, system paths, and hardware access. If this metadata is improperly managed, it can expose sensitive data.

Additionally, weak security practices like poor password management or misconfigurations within the container can open pathways for attackers. These vulnerabilities can be exploited to breach the container, potentially compromising the entire cloud infrastructure and leading to unauthorized access, data loss, or system downtime.

To mitigate these vulnerabilities, it’s crucial for DevOps teams to integrate security early in the container image management cycle. Implementing a “shift-left” security approach—embedding security checks and best practices early—alongside consistent monitoring of container images, ensures that potential weaknesses are caught before deployment, keeping applications and infrastructure safe from attacks.

What is Container Image Security?

Container image security is a comprehensive approach that ensures that the container images used in your environment are built from trusted sources, free from vulnerabilities, malware, or other security risks.

It involves verifying that the base image, libraries, and any custom components in your Dockerfile are from reliable sources and not tampered with.

Typically, base images like Alpine, Ubuntu, or BusyBox act as foundational layers, to which other components are added. Each addition creates a new image layer, and ensuring the integrity of these layers through regular security scanning is critical.

Container image security scanning is one of the many fundamental functions here, wherein images are scanned for known vulnerabilities. It uses specialized tools to scan potential risks, specifically looking for outdated libraries, insecure configurations, or any other vulnerabilities that can be exploited in a production environment.

In fact, Docker image security scanning applies to Docker images. Given Docker is heavily used, scanning is extremely important. It looks for vulnerabilities caused by running outdated software or insecure settings, which ultimately compromises the Docker runtime environment.

Why is Image Security Crucial in Containers?

In a containerized environment, image security is the foundational security level or layer that maintains the integrity and reliability of your applications.

Since a container image packages everything an app needs to run, any compromise has the potential for a high-level security incident and impact on all of your infrastructure.

1. CVSS Scoring

The Common Vulnerability Scoring System (CVSS) is a widely used framework for assessing the severity of vulnerabilities in container images and other software systems.

CVSS scores help organizations prioritize their response to vulnerabilities by providing a standardized measure of risk. These scores are calculated based on several metrics, including how much a vulnerability can be exploited, the impact on the system, and the potential for damage. The CVSS score ranges from 0 to 10, with higher scores indicating more severe vulnerabilities.

A vulnerability with a CVSS score of 9.8 is classified as critical, meaning it could allow an attacker to execute arbitrary code remotely with minimal user interaction. This level of severity often requires immediate remediation to prevent exploitation. Conversely, a vulnerability with a lower score might indicate a less critical issue but still needs to be addressed to reduce overall risk.

By utilizing CVSS scoring, organizations can make informed decisions about which vulnerabilities to prioritize based on their potential impact. This helps streamline patch management and focus resources on the most pressing security concerns.

2. Internal Storage of Images

Storing container images in private, internal registries is a fundamental practice for improving container security.

Unlike public registries, which are accessible to anyone on the internet, private registries provide a controlled environment where access can be tightly managed. This is crucial for protecting sensitive or proprietary container images from unauthorized access and potential tampering.

Private registries, such as Docker Trusted Registry (DTR) or other enterprise-level solutions, offer several advantages over public repositories. They allow organizations to enforce strict access controls, ensuring that only authorized users can upload, download, or modify container images. This reduces the risk of malicious code being introduced into the images.

Additionally, private registries often include built-in security features such as image signing, which provides a way to verify the authenticity and integrity of images. By using digital signatures, organizations can ensure that images come from trusted sources and have not been altered since their creation.

Private registries also support vulnerability scanning, which helps identify and remediate security issues before images are deployed.

3. Production vs. Non-Production Issues

In containerized environments, it’s important to differentiate between production and non-production environments for managing security effectively.

Production environments, where live applications and sensitive data reside, demand rigorous security measures to protect against threats. This includes implementing strong access controls, regular security audits, and continuous monitoring to detect and respond to potential vulnerabilities.

In contrast, non-production environments, such as development, testing, and staging, often have more relaxed security controls due to the need for rapid experimentation and iteration. However, this does not mean that security should be neglected.

Vulnerabilities discovered in non-production environments can potentially affect production systems if not properly managed. Therefore, it is crucial to apply security practices in non-production environments that align with the production environment’s standards.

For instance, non-production environments should still use secure coding practices, ensure proper handling of test data, and apply vulnerability scanning. Any vulnerabilities found should be addressed promptly to prevent them from migrating to production.

Effective segregation between production and non-production environments helps to minimize the risk of vulnerabilities impacting live systems and ensures that security practices are consistently applied across all stages of the application lifecycle.

4. Image Integrity and Verification

Maintaining the integrity of container images is crucial for ensuring that applications run securely and as intended. Image signing and cryptographic hashing are two key techniques used to verify the authenticity and integrity of container images.

Image Signing

Image signing involves applying digital signatures to container images, which confirms that the images originate from trusted sources and have not been tampered with since their creation. This process uses public key infrastructure (PKI) to create and verify signatures, providing a way to ensure that images are genuine.

By validating these signatures, organizations can prevent the deployment of compromised or malicious images.

Cryptographic Hashing

Cryptographic hashes, such as SHA-256, offer another layer of security by generating a unique hash value for each image. This hash value is used to detect any unauthorized changes or corruption.

By comparing the hash values of the deployed image with the original, organizations can identify if the image has been altered. Regular integrity checks help ensure that only secure and unmodified images are used in production environments.

5. Isolation Mechanisms and Multi-Tenancy Concerns

Containers are engineered to be somewhat isolated on a host system, whereas virtual machines (VM) provide a complete isolation layer.

Unlike VMs, which use hypervisors to create completely isolated environments with their own operating systems, containers share the host system’s kernel. This shared kernel introduces distinct security challenges, particularly in environments where multiple users or applications operate on the same host.

A vulnerability in one containerized application can permit an attacker to escape the container and gain access, risking the entire application—containerized or not—and the host system.

To address these challenges, several isolation mechanisms are employed within containers:

• Namespaces: Linux namespaces provide isolation at the process level, ensuring that containers operate in separate namespaces for processes, network interfaces, and file systems. While namespaces limit the visibility and access of processes to their own containers, they do not guarantee absolute separation from the host or other containers.
• Control Groups (cgroups): Cgroups manage and restrict the resources allocated to each container, such as CPU, memory, and disk I/O. This helps prevent one container from monopolizing system resources and affecting the performance or stability of other containers or the host system.
• Security Modules: Tools like SentinelOne enforce additional security policies. The tool applies mandatory access control policies to limit file system access and other capabilities.

Beyond isolation and resource management, ensuring the integrity of container images is critical to maintaining overall security.

Here’s how you can safeguard your containers:

• Image Signing and Verification: Use digital signatures to confirm the authenticity of container images, ensuring they come from trusted sources and remain untampered.
• Cryptographic Hashes: Generate and compare cryptographic hashes to verify that container images have not been modified or corrupted.
• Runtime Monitoring: Implement continuous monitoring to detect deviations or unauthorized changes in running containers, allowing for quick response to potential security breaches.

By applying these practices, organizations can effectively manage risks associated with shared kernels and multi-tenant environments, enhancing overall security and protecting against vulnerabilities.

5. Runtime Security and Drift Prevention

Even after a container is deployed, maintaining its security is essential.

Over time, containers will experience some “drift,” in which their running state deviates from the original image since the user or application may have updated the running instance or even had unauthorized changes. Any amount of drift introduces vulnerabilities that were not present at the time of the original deployment.

These may include:

• Configuration Drift: Changes in environment variables, network settings, or other configurations after deployment can lead to misconfigurations and security issues.
• Software Drift: Updates or modifications to the software within the container can introduce new vulnerabilities or create compatibility problems.
• File System Drift: Accumulation of temporary files or logs during runtime may affect the container’s performance and security posture.
• Network Drift: Alterations in network settings or exposed ports can open new attack vectors or disrupt connectivity.

To effectively manage and mitigate drift, leverage tools that provide continuous runtime monitoring of containers. These tools can detect deviations from the original configuration and unauthorized changes, enabling swift action to address any issues.

Implementing automated compliance checks helps enforce security policies and maintain the container’s intended state.

Additionally, adopting immutable infrastructure practices—where containers are replaced rather than modified—further reduces the risk of drift and ensures robust security.

How to Perform Container Image Security Scanning?

Protecting your container images requires many steps. Throughout the CI/CD pipeline, you should use both automated tools and good practices.

The first step is to scan container images for security issues during the build process. This means using special scanners to examine each part of your container image to find any known weak spots, including common vulnerabilities and exposures (CVEs).

These scanners compare code or points (dependencies) that could be dangerous. They also check settings and point out any old dependencies or secrets that might be hidden inside.

The next step involves implementing tough image signing rules to ensure that images that have been checked before can be used. This is called image signing, which uses code signatures to verify where the image came from and that no one has changed it or added any harmful code.

It’s also crucial to store your images in private container registries instead of public ones. The SentinelOne Cloud Workload Protection Platform (CWPP) works well with Snyk Container, allowing users to log in to private container registries.

This integration makes incident triage easier, prevents security incidents from spreading in container workloads, and fixes issues in production by tracing them back to the application source code. This reduces the risk of using compromised images and ensures that verified images are used.

To finish up, you should add regular compliance checks and vulnerability assessments to how you manage your containers. These assessments should run at set times. This ensures all images follow your security rules and meet any regulatory requirements you have.

Common Vulnerabilities in Docker Images

Docker images pack multiple layers of software, each hiding its weak spots.

Here are some of the most common and tricky weak points that can pop up:

1. Old and Vulnerable Base Images

Docker images often depend on base images like Ubuntu, Alpine, or CentOS. If these are not kept up-to-date, they can have known weak spots.

For instance, outdated versions of glibc or openssl in base images can leave containers open to remote code execution (RCE) or privilege escalation attacks.

Hence, it’s crucial to monitor and update base images to incorporate security patches and reduce the risk of exploitation.

2. Unsafe Third-Party Dependencies

Docker image applications often include third-party libraries and dependencies that can have an impact on security.

Take a Node.js app as an example. It might use npm packages with known security flaws, like Prototype Pollution in lodash or regular expression denial of service (ReDoS) attacks in older minimatch versions.

To address these risks, it is crucial to utilize robust vulnerability scanning tools. Software like Snyk and OWASP Dependency-Check can help identify and assess vulnerabilities in your third-party libraries.

Another vital step in maintaining security is regularly updating your dependencies. By applying security patches and upgrading to newer, more secure versions of libraries, you reduce the risk of exploitation.

Additionally, evaluating and minimizing the number of third-party libraries included in your project can significantly reduce potential vulnerabilities. Opt for well-maintained and trusted packages to minimize the attack surface. Regularly review and audit these dependencies to ensure they do not introduce new security risks.

3. Dockerfile Setup Errors

Mistakes in Dockerfile setups can leave containers open to security threats.

A common setup mistake is using the root user by default, which can lead to hackers gaining more power than they should. Also, putting sensitive info like API keys or passwords in the Dockerfile or as environment variables can let unauthorized people in if someone cracks the image.

To mitigate these risks, follow best practices like:

• Using non-privileged users whenever possible to reduce potential attack vectors
• Building images in multiple stages to ensure that sensitive information does not end up in the final image
• Avoiding exposure of sensitive information in environment variables and using secure methods to handle credentials

4. Unpatched CVEs in the App Code

The app code packed into Docker images might have unfixed common vulnerabilities and exposures (CVEs). For instance, CVE-2022-23307, a serious weakness in the Log4j library, could let attackers run any code they want by sending tricky log messages.

Regular scans for CVEs with container image security tools like SentinelOne are key to spotting and fixing these weak points before hackers can exploit them.

5. Excessive Layering and Bulk

Docker images with too many layers or unnecessary software can make attacks easier. Each extra layer could be a weak spot, and unneeded software packages might bring in security problems.

For example, putting a full JDK instead of a JRE in a production image could open up more ways to attack without adding needed features. Using bare-bones base images and the must-have dependencies cuts down this risk.

To address this, opt for minimal base images and include only the essential dependencies required for your application to function. By keeping your Docker images lean, you not only reduce their complexity but also minimize the number of potential security issues. A streamlined image with only the necessary components lowers the risk of exploitation by limiting the opportunities for attackers to target vulnerabilities.

6. Misconfigured Network Options

Docker images might open unnecessary ports or use unsafe network protocols. Bad actors can use these to access containers or move around inside a network.

For instance, leaving SSH ports open on a container without proper safeguards can make it a target for brute-force attacks. To prevent such weak spots, it’s crucial to put into action network security best practices. These include firewalls, network namespaces, and locking down exposed ports.

For example,

• Configure firewalls to block unauthorized access
• Use network namespaces to isolate and secure your containers
• Carefully limit the number of exposed ports

By managing network configurations with security in mind, you can significantly reduce the likelihood of unauthorized access and enhance the overall security posture of your Docker environment.

Securing the Foundation of Containerized Applications

Container image security plays a key role in modern app development and deployment. As more companies use containers, protecting these core building blocks becomes crucial. To secure container images, you need to follow these best practices:

• Thorough Scanning and Continuous Integration/Continuous Deployment (CI/CD) Checks: Security experts cannot stress enough the importance of integrating robust scanning tools throughout the CI/CD pipeline. This approach helps identify and address vulnerabilities early in the development cycle, reducing potential risks.
• Adopting Best Practices: Utilizing minimal base images and implementing strict access controls, companies can limit the attack surface and enhance overall security.
• Private Registries and Image Signing: The use of private registries and image signing to secure the supply chain ensures that container images are vetted and protected from unauthorized alterations.
• Ongoing Monitoring: Continuous monitoring of both build and runtime environments is necessary. By diligently tracking potential vulnerabilities and compliance issues, organizations can ensure a robust and secure container ecosystem.

By prioritizing container image security, companies can reduce their weak spots, adhere to rules, and establish a solid foundation for their containerized apps.

Protect Your Docker Containers with SentinelOne’s Cloud Workload Security for Containers

As cyberattacks become increasingly sophisticated, traditional security measures are often insufficient. SentinelOne’s Cloud Workload Security (CWS) for containers, part of the Singularity™ platform, offers a cutting-edge solution designed to address these modern threats effectively. Here’s how SentinelOne enhances container image security:

• Real-Time Threat Protection: Singularity CWS continuously monitors and protects your containerized workloads from threats like ransomware and unknown vulnerabilities. Its AI-driven technology ensures rapid detection and response, safeguarding your environments across AWS, Azure, Google Cloud, and private data centers.
• Incident Investigation and Threat Hunting: Utilizing the Singularity Data Lake, SentinelOne provides comprehensive insights into your workload’s activity. This tool helps in investigating incidents and conducting threat hunts. The Workload Flight Data Recorder™ assists in recovering from incidents by removing problematic workloads and minimizing financial loss and damage.
• Broad Compatibility: SentinelOne supports a wide array of containerized workloads, including 14 major Linux distributions, three popular container runtimes, and both managed and self-run Kubernetes services.
• Robust Threat Detection: With capabilities designed to detect and respond to threats in real-time, SentinelOne’s platform contributes significantly to a layered cloud security strategy. It also offers wide-ranging data storage choices and built-in Kubernetes information, giving security teams a linked chain of visibility and response tools to boost incident handling and threat searching, which are crucial as Linux becomes a larger target for attackers.

For a comprehensive container image security audit and to see SentinelOne in action, book a free demo today and experience how SentinelOne can fortify your container security strategy.

Conclusion

As with most security challenges, there is no one-size-fits-all solution for container security. The technical, operational, and organizational aspects of protecting your company’s container images often involve multiple teams and responsibilities, adding to the complexity. Instead of letting this complexity hinder your efforts, seek tools that facilitate collaboration and help you understand where goals, risks, and priorities intersect.

It’s crucial to choose container security solutions that are transparent about their capabilities and provide assistance in areas outside their core offerings. SentinelOne’s Singularity Cloud Workload Security for Containers delivers comprehensive protection by integrating seamlessly into your DevOps environment, offering robust visibility and automated defenses tailored to your needs.

Whether you’re new to container security or have years of experience, SentinelOne is here to guide you toward a more secure and stable environment.

Book a tailored demo today to see how SentinelOne can enhance your container image security!

FAQs

How secure are Docker images?

Docker images offer isolation but are not inherently secure. Reports often show that over 50% of Docker images contain critical vulnerabilities, highlighting the need for robust security measures. These safety practices and tools are used during development and deployment.

What steps would you take to secure a container image?

To effectively secure a container image, it’s essential to implement several key practices that address potential vulnerabilities and ensure the integrity of your containers, including:

• Scanning for Vulnerabilities: Regularly check images for known security issues.
• Using Minimal Base Images: Opt for images with only essential components.
• Implementing Image Signing: Sign images to verify authenticity and integrity.
• Enforcing Access Controls: Restrict access using role-based controls and secure authentication.

What are Docker image vulnerabilities?

Common vulnerabilities include outdated base images, insecure third-party dependencies, misconfigurations in Dockerfiles, unpatched CVEs in application code, and excessive layering.

Can you make Docker images private?

Yes, Docker images can be made private by using private container registries or repositories with restricted access.

What are the three main security threats on the cloud?

The three main security threats on the cloud are data breaches, misconfigured cloud settings, and insecure APIs.