CVE-2021-41254 : Exploit Details and Defense Strategies

Kustomize-controller, a Kubernetes operator within fluxcd, was susceptible to privilege escalation allowing unauthorized users to gain cluster admin privileges.

Understanding CVE-2021-41254

What is CVE-2021-41254?

Kustomize-controller had a vulnerability that enabled non-admin users to execute commands and potentially gain cluster admin privileges.

The Impact of CVE-2021-41254

The vulnerability allowed unauthorized users to execute commands within the kustomize-controller container, leading to potential privilege escalation in multi-tenant environments.

Technical Details of CVE-2021-41254

Vulnerability Description

The flaw in kustomize-controller allowed users to embed shell scripts in Kubernetes Secrets, enabling the execution of commands under the Service Account of kustomize-controller.

Affected Systems and Versions

Product: kustomize-controller
Vendor: fluxcd
Versions affected: < 0.15.0

Exploitation Mechanism

Unauthorized users could run

kubectl

commands within the container OS, gaining cluster admin privileges in affected versions.

Mitigation and Prevention

Immediate Steps to Take

Update to kustomize-controller v0.15.0 or newer versions.
Utilize Kubernetes validation webhooks like Gatekeeper OPA or Kyverno to prevent unauthorized actions.

Long-Term Security Practices

Regularly review and restrict permissions for creating Flux Kustomization objects.
Implement secure coding practices to avoid command injections.

Patching and Updates

Apply patches and updates promptly to ensure the latest security fixes are in place.