Kubernetes NodeRestriction Flaw Lets Nodes Bypass Resource Authorization

Kubernetes NodeRestriction Flaw Lets Nodes Bypass Resource Authorization

A critical security vulnerability (CVE-2025-4563) in Kubernetes allows nodes to bypass authorization checks for dynamic resource allocation, potentially enabling privilege escalation in affected clusters.

The flaw resides in the NodeRestriction admission controller, which fails to validate resource claim statuses during pod creation when the DynamicResourceAllocation feature is enabled.

This oversight permits compromised nodes to create unauthorized mirror pods that access restricted resources, though exploitation requires specific configurations: the vulnerable feature (disabled by default) must be active alongside static pod usage.

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Technical Impact and Severity

According to the Github report, the vulnerability affects kube-apiserver versions 1.32.0-1.32.5 and 1.33.0-1.33.1, with a CVSS score of 2.7 (Low severity). 

Attribute Details
CVE ID CVE-2025-4563
Affected Versions kube-apiserver: v1.32.0-v1.32.5, v1.33.0-v1.33.1
CVSS Score 2.7 (Low)
Primary Risk Privilege escalation via unauthorized dynamic resource access

While the attack vector is network-based, exploitation demands high privileges and causes low availability impact without compromising confidentiality or integrity. Notably:

  • Privilege escalation: Compromised nodes can create mirror pods to access unauthorized resources.
  • Limited exposure: Only clusters using both DynamicResourceAllocation and static pods are vulnerable.
  • Default safety: The DynamicResourceAllocation feature is disabled by default in Kubernetes.

Mitigation Strategies

Immediate actions include:

  1. Update Kubernetes to patched versions (v1.32.6 or v1.33.2).
  2. Disable DynamicResourceAllation via API server parameters if unable to patch immediately.
  3. Audit cluster configurations using:
kubectl get ResourceClaim --all-namespaces
kubectl get pods --all-namespaces -o json | jq -r '.items[] | select(.metadata.annotations["kubernetes.io/config.mirror"] == "true") | "(.metadata.namespace)/(.metadata.name)"'

to identify vulnerable setups.

Cloud providers like Azure Kubernetes Service (AKS) remain unaffected as they don’t enable the vulnerable feature. 

Users should prioritize patching or disabling the feature gate to prevent potential exploitation, despite the low severity rating.

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