Kubernetes Configuration File Group Readability: An Insecurity

Kubernetes has become the de facto standard for container orchestration in modern software development. Its configuration files, often in YAML or JSON format, are crucial for defining the desired state of applications and resources within a Kubernetes cluster. However, a common security oversight is leaving these configuration files group - readable. This blog post will explore why having group - readable Kubernetes configuration files is insecure, its implications, and how to mitigate these risks.

Table of Contents

  1. [Core Concepts](#core - concepts)
  2. [Typical Usage Example](#typical - usage - example)
  3. [Common Practices and Associated Risks](#common - practices - and - associated - risks)
  4. [Best Practices](#best - practices)
  5. Conclusion
  6. References

Core Concepts

Kubernetes Configuration Files

Kubernetes configuration files are used to define various objects in the cluster, such as pods, services, deployments, and more. These files contain sensitive information like API keys, authentication tokens, and network configurations. They are the blueprint for how your application should run within the Kubernetes ecosystem.

File Permissions

In Unix - like operating systems, file permissions are divided into three categories: owner, group, and others. Each category can have read (r), write (w), and execute (x) permissions. When a file is group - readable, all users belonging to the same group as the file’s owner can view the file’s contents.

Security Risks of Group - Readable Configuration Files

The main security risk of having group - readable Kubernetes configuration files is that any user in the same group can access sensitive information. This could lead to unauthorized access to the Kubernetes cluster, malicious modifications of the configuration, or exposure of critical data. For example, an attacker within the group could use the API keys in the configuration file to gain unauthorized access to the cluster and disrupt the services running on it.

Typical Usage Example

Let’s assume you have a Kubernetes deployment file named deployment.yaml that looks like this:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my - app - deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my - app
  template:
    metadata:
      labels:
        app: my - app
    spec:
      containers:
      - name: my - app - container
        image: my - app:latest
        env:
        - name: API_KEY
          value: "abc123def456"

If the file permissions are set such that the group has read access (-rw-r--r--), any user in the same group as the file’s owner can view the API_KEY value. This key could be used to access external services or perform unauthorized actions within the Kubernetes cluster.

Common Practices and Associated Risks

Common Practices

  • Shared Development Environments: In a team - based development environment, developers often share a common set of Kubernetes configuration files. These files may be stored in a shared directory, and the default permissions could be set to group - readable for easy access.
  • Automated Scripts: Automated scripts may create or modify Kubernetes configuration files. If these scripts do not explicitly set the correct file permissions, the files may end up being group - readable.

Associated Risks

  • Data Leakage: Sensitive information such as API keys, passwords, and tokens can be leaked to unauthorized users within the group.
  • Unauthorized Access: Malicious users within the group can use the leaked information to gain unauthorized access to the Kubernetes cluster and perform actions like creating, modifying, or deleting resources.
  • Service Disruption: Incorrect or malicious modifications to the configuration files can lead to service disruptions, affecting the availability of applications running on the cluster.

Best Practices

Set Appropriate File Permissions

  • When creating or modifying Kubernetes configuration files, set the file permissions so that only the owner has read and write access. You can use the chmod command in Unix - like systems:
chmod 600 deployment.yaml

This sets the file permissions to -rw-------, where only the owner can read and write the file.

Use Secret Management Tools

  • Instead of hard - coding sensitive information in the configuration files, use Kubernetes secrets. Secrets are encrypted objects in Kubernetes that can store sensitive data like API keys and passwords. You can reference these secrets in your configuration files without exposing the actual values.
apiVersion: v1
kind: Secret
metadata:
  name: my - app - secret
type: Opaque
data:
  API_KEY: YWJjMTIzZGVmNDU2 # Base64 - encoded value of "abc123def456"

---

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my - app - deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my - app
  template:
    metadata:
      labels:
        app: my - app
    spec:
      containers:
      - name: my - app - container
        image: my - app:latest
        env:
        - name: API_KEY
          valueFrom:
            secretKeyRef:
              name: my - app - secret
              key: API_KEY

Limit Access to Configuration Files

  • Only grant access to the configuration files to users who really need it. Use role - based access control (RBAC) in Kubernetes to restrict who can view, create, and modify the configuration files.

Conclusion

In conclusion, having group - readable Kubernetes configuration files is a significant security risk. It can lead to data leakage, unauthorized access, and service disruptions. By understanding the core concepts, being aware of common practices and associated risks, and following best practices such as setting appropriate file permissions, using secret management tools, and limiting access, software engineers can significantly enhance the security of their Kubernetes clusters.

References