Kubernetes has become the backbone for cloud-native workloads, and Ruby developers often turn to the kubeclient gem for interacting with Kubernetes APIs. But did you know that a serious security flaw, CVE-2022-0759, put many Ruby applications at risk of Man-in-the-Middle (MITM) attacks? Let’s break it down in simple terms, explore what went wrong with kubeclient’s kubeconfig parsing, look at code evidence, and cover how to fix and secure your applications.

What is CVE-2022-0759?

CVE-2022-0759 is a vulnerability found in kubeclient (all versions up to but excluding v4.9.3), the popular Ruby client for Kubernetes. The vulnerability happens when kubeclient parses kubeconfig files—a standard way of setting up Kubernetes API authentication.

The flaw:
If your kubeconfig file does *not* configure a custom Certificate Authority (CA) for verifying server certificates, kubeclient mistakenly disables verification entirely (VERIFY_NONE). As a result, your Ruby app accepts any TLS certificate when connecting to a Kubernetes API, exposing it to man-in-the-middle attacks.

Why Is This Dangerous?

A server pretending to be your Kubernetes API can intercept sensitive data, inject malicious responses, or gain unauthorized access. Certificate verification is there to prevent this exact scenario—so disabling it is as bad as leaving the front door open.

How to verify the server (Trusted CA certificate)

If you skip the CA section, kubeclient should ideally default to system CAs or fail. But the buggy versions did this instead:

Faulty Certificate Verification Logic

require 'kubeclient'
config = Kubeclient::Config.read('/path/to/kubeconfig')
client = Kubeclient::Client.new(
  config.context.api_endpoint,
  config.context.api_version,
  ssl_options: config.context.ssl_options # <-- UA-oh!
)

If ssl_ca_cert is not set in your context, kubeclient incorrectly sets up the SSL connection like so:

OpenSSL::SSL::VERIFY_NONE # Bad!

This means any certificate is accepted, even a self-signed or malicious one.

Attacker controls the network (e.g., shared Wi-Fi).

2. Your Ruby program uses kubeclient to connect to https://api-server.

Sample Code Snippet Showing the Problem

require 'kubeclient'
require 'openssl'

KUBECONFIG_CONTENT = <<~YAML
apiVersion: v1
clusters:
- cluster:
    server: https://malicious-api-server
  name: badcluster
contexts:
- context:
    cluster: badcluster
    user: fakeuser
  name: badcontext
current-context: badcontext
users:
- name: fakeuser
  user:
    token: 'faketoken'
YAML

File.write('tempconfig', KUBECONFIG_CONTENT)
config = Kubeclient::Config.read('tempconfig')
client = Kubeclient::Client.new(
  config.context.api_endpoint,
  'v1',
  ssl_options: config.context.ssl_options
)

# No CA = accepts any certificate!
puts client.ssl_options[:verify_ssl] # Outputs , which means VERIFY_NONE

With this setup, connecting to https://malicious-api-server works, *no complaints*. A real Kubernetes client or browser would scream about bad certificates.

Attackers could read, modify, or delete Kubernetes resources

- Apps and CI/CD pipelines without custom CA settings are especially exposed

Upgrade kubeclient

Patch is included in v4.9.3.

gem update kubeclient

`
- Always specify certificate verification
Add CA data in your kubeconfig, or make sure kubeclient uses system CAs.

- Audit your code
Check how you’re reading kubeconfig and passing ssl_options.

- Test in Dev and CI
Simulate a man-in-the-middle to make sure your clients complain about bad certs after patching.

---

## References & Further Reading

- CVE-2022-0759 in NVD
- Kubeclient Security Announcement
- Kubeclient Release with Patch
- Exploit Anatomy (MitM attacks)

---

## Conclusion

CVE-2022-0759 is a textbook example of why certificate verification matters. If you’re running Ruby apps with kubeclient, review your versions and configs immediately. Always trust, but verify—especially with TLS.

If you found this post helpful, share it or check out the full patch diff to see how the kubeclient team fixed it! Stay safe and secure your clusters.

Timeline

Published on: 03/25/2022 19:15:00 UTC
Last modified on: 04/07/2022 19:13:00 UTC