Understanding Kernel Capabilities

Oct 13, 2025 by pinkandtrash.com 147 views

Introduction

In the realm of containerized applications, security is a top priority. The Grafana Synthetic Monitoring Agent, a popular tool for monitoring and analyzing application performance, has a Dockerfile that assigns a specific kernel capability to the binary. This capability, known as net_cap_raw, is assigned on Line 15 of the Dockerfile. However, this capability is not allowed in many enterprise settings, including our own environment. In this article, we will explore the possibility of removing this capability or creating a "hardened" image that does not assign it.

Understanding Kernel Capabilities

Kernel capabilities are a way to grant a process specific privileges without giving it full root access. This allows for a more fine-grained control over the privileges of a process, making it easier to secure the system. The net_cap_raw capability, in particular, allows a process to capture and manipulate network packets, which can be a security risk if not properly managed.

The Issue with `net_cap_raw`

The net_cap_raw capability is assigned to the /usr/local/bin/synthetic-monitoring-agent binary in the Grafana Synthetic Monitoring Agent Dockerfile. This capability is not allowed in many enterprise settings, including our own environment, due to security concerns. Assigning this capability to a process can potentially allow it to capture and manipulate network packets, which can be used for malicious purposes.

Removing the Capability

Removing the net_cap_raw capability from the Dockerfile is a straightforward process. However, it requires careful consideration of the potential consequences. If the capability is removed, the process may not be able to function correctly, or it may require additional configuration to work around the lack of capability.

Creating a "Hardened" Image

Creating a "hardened" image that does not assign the net_cap_raw capability requires a more complex approach. This involves creating a custom Dockerfile that removes the capability and any other unnecessary privileges. It also requires testing the image to ensure that it functions correctly and does not introduce any security vulnerabilities.

Step-by-Step Guide to Creating a "Hardened" Image

Step 1: Create a Custom Dockerfile

Create a new Dockerfile that removes the net_cap_raw capability and any other unnecessary privileges. This can be done by using the RUN command to remove the capability and the COPY command to copy the necessary files.

FROM grafana/synthetic-monitoring-agent:latest

# Remove the net_cap_raw capability
RUN setcap -r /usr/local/bin/synthetic-monitoring-agent

# Copy the necessary files
COPY --from=grafana/synthetic-monitoring-agent:latest /usr/local/bin/synthetic-monitoring-agent /usr/local/bin/synthetic-monitoring-agent

Step 2: Build the Image

Build the image using the custom Dockerfile.

docker build -t my-hardened-image .

Step 3: Test the Image

Test the image to ensure that it functions correctly and does not introduce any security vulnerabilities.

docker run -it my-hardened-image

Step 4: Push the Image to a Registry

Push the image to a registry, such as Docker Hub, to make it available for use in other environments.

docker tag my-hardened-image <username>/my-hardened-image
docker push <username>/my-hardened-image

Conclusion

In conclusion, removing the net_cap_raw capability from the Grafana Synthetic Monitoring Agent Dockerfile or creating a "hardened" image that does not assign it requires careful consideration of the potential consequences. However, with a step-by-step guide, it is possible to create a custom Dockerfile that removes the capability and any other unnecessary privileges. By following these steps, you can create a "hardened" image that is more secure and suitable for use in enterprise environments.

Recommendations

Always test the image to ensure that it functions correctly and does not introduce any security vulnerabilities.
Use a custom Dockerfile to remove unnecessary privileges and capabilities.
Push the image to a registry, such as Docker Hub, to make it available for use in other environments.
Consider using a containerization platform, such as Kubernetes, to manage and deploy the image.

Future Work

Investigate the possibility of using a different kernel capability that is more secure and suitable for use in enterprise environments.
Explore the use of other security features, such as SELinux or AppArmor, to further harden the image.
Consider using a more secure communication protocol, such as TLS, to encrypt data in transit.
Excessive Kernel NET Capabilities: A Concern for Enterprise Environments ===========================================================

Q&A: Excessive Kernel NET Capabilities

Q: What is the `net_cap_raw` capability and why is it a concern?

A: The net_cap_raw capability allows a process to capture and manipulate network packets. This can be a security risk if not properly managed, as it can potentially allow a process to intercept and modify sensitive data.

Q: Why is the `net_cap_raw` capability assigned to the Grafana Synthetic Monitoring Agent?

A: The net_cap_raw capability is assigned to the Grafana Synthetic Monitoring Agent to allow it to capture and analyze network traffic. However, this capability is not allowed in many enterprise settings, including our own environment, due to security concerns.

Q: Can I remove the `net_cap_raw` capability from the Dockerfile?

A: Yes, you can remove the net_cap_raw capability from the Dockerfile. However, it requires careful consideration of the potential consequences. If the capability is removed, the process may not be able to function correctly, or it may require additional configuration to work around the lack of capability.

Q: How do I create a "hardened" image that does not assign the `net_cap_raw` capability?

A: To create a "hardened" image that does not assign the net_cap_raw capability, you need to create a custom Dockerfile that removes the capability and any other unnecessary privileges. You also need to test the image to ensure that it functions correctly and does not introduce any security vulnerabilities.

Q: What are the benefits of creating a "hardened" image?

A: Creating a "hardened" image provides several benefits, including:

Improved security: By removing unnecessary privileges and capabilities, you can reduce the attack surface of the image.
Reduced risk: By creating a custom image that is tailored to your specific needs, you can reduce the risk of introducing security vulnerabilities.
Increased flexibility: By creating a custom image, you can add or remove features as needed, without affecting the underlying infrastructure.

Q: How do I test a "hardened" image?

A: To test a "hardened" image, you need to run it in a controlled environment and verify that it functions correctly. You should also test the image for any security vulnerabilities or issues.

Q: What are some best practices for creating a "hardened" image?

A: Some best practices for creating a "hardened" image include:

Use a custom Dockerfile to remove unnecessary privileges and capabilities.
Test the image thoroughly to ensure that it functions correctly and does not introduce any security vulnerabilities.
Use a containerization platform, such as Kubernetes, to manage and deploy the image.
Consider using a more secure communication protocol, such as TLS, to encrypt data in transit.

Q: Can I use a different kernel capability that is more secure and suitable for use in enterprise environments?

A: Yes, you can use a different kernel capability that is more secure and suitable for use in enterprise environments. However, you need to carefully evaluate the capabilities and privileges required by your application and ensure that they are aligned with your security policies and procedures.

Q: What are some common security risks associated with kernel capabilities?

A: Some common security risks associated with kernel capabilities include:

Privilege escalation: Kernel capabilities can be used to escalate privileges and gain access to sensitive data or systems.
Data interception: Kernel capabilities can be used to intercept and modify sensitive data in transit.
Denial of service: Kernel capabilities can be used to disrupt or deny service to a system or application.

Q: How can I mitigate the risks associated with kernel capabilities?

A: To mitigate the risks associated with kernel capabilities, you can:

Use a custom Dockerfile to remove unnecessary privileges and capabilities.
Test the image thoroughly to ensure that it functions correctly and does not introduce any security vulnerabilities.
Use a containerization platform, such as Kubernetes, to manage and deploy the image.
Consider using a more secure communication protocol, such as TLS, to encrypt data in transit.