CVE-2020-8569 in CSI snapshot-controller
Summary
by MITRE • 01/22/2021
Kubernetes CSI snapshot-controller prior to v2.1.3 and v3.0.2 could panic when processing a VolumeSnapshot custom resource when: - The VolumeSnapshot referenced a non-existing PersistentVolumeClaim and the VolumeSnapshot did not reference any VolumeSnapshotClass. - The snapshot-controller crashes, is automatically restarted by Kubernetes, and processes the same VolumeSnapshot custom resource after the restart, entering an endless crashloop. Only the volume snapshot feature is affected by this vulnerability. When exploited, users can’t take snapshots of their volumes or delete the snapshots. All other Kubernetes functionality is not affected.
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Analysis
by VulDB Data Team • 02/19/2021
The vulnerability identified as CVE-2020-8569 represents a critical panic condition within the Kubernetes Container Storage Interface CSI snapshot-controller component that affects versions prior to v2.1.3 and v3.0.2. This flaw manifests when the snapshot-controller encounters a VolumeSnapshot custom resource that references a non-existent PersistentVolumeClaim without a corresponding VolumeSnapshotClass specification. The technical implementation fails to properly handle this edge case, leading to a system panic that causes the controller to crash and subsequently restart in a continuous loop. This particular vulnerability resides in the snapshot controller's resource processing logic where it lacks proper validation and error handling mechanisms for malformed VolumeSnapshot references, creating a denial-of-service condition that specifically targets the snapshot functionality while leaving other Kubernetes operations unaffected.
The operational impact of this vulnerability extends beyond simple service disruption as it creates a persistent crashloop that prevents users from performing any snapshot operations on their volumes. When the snapshot-controller crashes and restarts, it processes the same problematic VolumeSnapshot resource repeatedly, causing an endless cycle that consumes system resources and prevents legitimate snapshot operations from completing. This behavior directly violates the principle of system resilience and fault tolerance that Kubernetes aims to provide. The vulnerability operates at the level of custom resource management within the Kubernetes API server, where the controller's failure to gracefully handle missing references creates a cascading effect that can impact storage operations across multiple workloads. This issue particularly affects environments that rely heavily on dynamic volume provisioning and snapshot-based backup strategies, making it a significant concern for production deployments.
The root cause of this vulnerability can be traced to insufficient input validation and error handling within the snapshot-controller's processing pipeline. According to CWE classification, this represents a weakness in resource management where the system fails to properly handle invalid or missing references, specifically CWE-457: Use of Uninitialized Variable. The flaw demonstrates poor defensive programming practices where the controller does not implement proper null-checking or fallback mechanisms when encountering missing PersistentVolumeClaim references. From an ATT&CK framework perspective, this vulnerability aligns with T1486: Data Encrypted for Impact, as it prevents legitimate data operations while maintaining system availability for other functions. The vulnerability creates a state where the system becomes unresponsive to snapshot-related operations, effectively creating a form of operational denial-of-service that impacts storage management capabilities.
Mitigation strategies for CVE-2020-8569 require immediate upgrade of the CSI snapshot-controller to versions v2.1.3 or v3.0.2 where the panic condition has been resolved. Organizations should implement proactive monitoring of the snapshot-controller pods to detect and respond to crashloop conditions before they escalate. System administrators should also validate all VolumeSnapshot resources before creation to ensure that referenced PersistentVolumeClaims exist and that proper VolumeSnapshotClass specifications are included. Additionally, implementing proper resource quotas and limits can help prevent the crashloop from consuming excessive system resources while the controller attempts to process malformed resources. Security teams should consider implementing automated remediation procedures that can detect and delete problematic VolumeSnapshot resources when they trigger controller panics, thereby preventing the continuous restart cycles. Regular auditing of snapshot operations and custom resource definitions should be conducted to identify and remediate similar validation gaps in other controller components.