CVE-2024-0793 Overview
A denial of service vulnerability was discovered in Kubernetes kube-controller-manager (KCM). This flaw occurs when applying an initial Horizontal Pod Autoscaler (HPA) configuration YAML that lacks a .spec.behavior.scaleUp block, causing KCM pods to enter a restart churn cycle, effectively resulting in denial of service conditions for the Kubernetes control plane.
Critical Impact
This vulnerability can cause complete disruption of Kubernetes cluster operations by forcing the kube-controller-manager into continuous restart loops, impacting cluster scaling, resource management, and overall availability.
Affected Products
- Kubernetes kube-controller-manager
- Red Hat OpenShift Container Platform
- Kubernetes distributions utilizing the affected kube-controller-manager component
Discovery Timeline
- November 17, 2024 - CVE-2024-0793 published to NVD
- November 18, 2024 - Last updated in NVD database
Technical Details for CVE-2024-0793
Vulnerability Analysis
This vulnerability is classified as an Improper Input Validation flaw (CWE-20) within the Kubernetes kube-controller-manager component. The issue manifests when processing Horizontal Pod Autoscaler (HPA) configuration files that do not include the .spec.behavior.scaleUp block.
When such a malformed HPA configuration is initially applied to a Kubernetes cluster, the kube-controller-manager fails to properly handle the missing configuration block. This causes the KCM pods to crash and enter a continuous restart cycle, effectively creating a denial of service condition. The vulnerability is particularly concerning because it can be triggered through legitimate cluster operations by any user with permissions to create or modify HPA resources.
The attack can be executed remotely over the network and requires low privileges to exploit. While it does not impact data confidentiality or integrity, it severely affects service availability. The scope is changed, meaning the vulnerability can impact resources beyond its security scope, affecting the entire Kubernetes control plane functionality.
Root Cause
The root cause of this vulnerability lies in improper input validation within the kube-controller-manager's HPA processing logic. Specifically, the controller does not properly handle cases where the .spec.behavior.scaleUp configuration block is absent from an HPA manifest. The missing null check or default value handling causes the controller to encounter an unhandled exception state, triggering pod crashes.
Attack Vector
The attack vector is network-based, requiring an authenticated user with permissions to create or modify HPA resources in the Kubernetes cluster. An attacker could exploit this vulnerability by:
- Crafting a malicious HPA configuration YAML file without the .spec.behavior.scaleUp block
- Applying this configuration to the target Kubernetes cluster using kubectl apply or the Kubernetes API
- The kube-controller-manager processes the invalid configuration and crashes
- Kubernetes attempts to restart the KCM pod, but it crashes again upon processing the same HPA resource
- This creates a restart loop that disrupts control plane operations
The vulnerability can be triggered by submitting an HPA manifest similar to the following structure that omits the scaleUp behavior specification while including other behavior settings. For detailed technical information, refer to the GitHub OpenShift PR #1876.
Detection Methods for CVE-2024-0793
Indicators of Compromise
- Unusual restart patterns in kube-controller-manager pods with CrashLoopBackOff status
- HPA resources in the cluster that lack .spec.behavior.scaleUp configuration blocks
- Control plane instability or degraded cluster responsiveness
- Error logs in kube-controller-manager indicating nil pointer or validation failures related to HPA processing
Detection Strategies
- Monitor kube-controller-manager pod health and restart counts using Kubernetes metrics
- Implement admission controllers or OPA policies to validate HPA configurations before application
- Review cluster audit logs for HPA creation events, particularly those with incomplete behavior specifications
- Set up alerting for control plane component availability degradation
Monitoring Recommendations
- Configure Prometheus alerts for kube-controller-manager restart thresholds exceeding normal baselines
- Enable Kubernetes audit logging to capture all HPA create and update operations
- Deploy cluster health monitoring to detect control plane service disruptions
- Implement SentinelOne Kubernetes Workload Protection for real-time container and pod behavior analysis
How to Mitigate CVE-2024-0793
Immediate Actions Required
- Review all existing HPA configurations in the cluster for missing .spec.behavior.scaleUp blocks
- Implement admission webhook policies to reject HPA manifests without complete behavior specifications
- Update affected Kubernetes or OpenShift installations to patched versions
- Monitor kube-controller-manager pods for stability issues
Patch Information
Red Hat has released security advisories addressing this vulnerability. Organizations running affected versions should apply the following patches:
For OpenShift users, the fix is available through GitHub OpenShift PR #1876. Additional details about the vulnerability and remediation are available in the Red Hat CVE Details for CVE-2024-0793.
Workarounds
- Ensure all HPA configurations include complete .spec.behavior blocks with both scaleUp and scaleDown specifications
- Implement Kubernetes ValidatingAdmissionWebhook to block incomplete HPA configurations
- Use GitOps practices to review and validate HPA manifests before cluster deployment
- Restrict HPA creation permissions using RBAC to trusted users and service accounts only
# Example: Validating HPA configurations before applying
# Check for missing scaleUp behavior in HPA manifests
kubectl get hpa -A -o json | jq '.items[] | select(.spec.behavior != null and .spec.behavior.scaleUp == null) | {namespace: .metadata.namespace, name: .metadata.name}'
# Apply RBAC restrictions for HPA management
kubectl create clusterrole hpa-restricted --verb=create,update,patch --resource=horizontalpodautoscalers --dry-run=client -o yaml
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
