Twin Path Traversal Vulnerabilities in Kubernetes CSI Drivers Expose Tenant Data
Two critical path traversal vulnerabilities in Kubernetes CSI drivers for NFS and SMB allow attackers to access cross-tenant data and potentially disrupt nodes.
SentinelOne Labs has disclosed two critical path traversal vulnerabilities, CVE-2026-3864 and CVE-2026-3865, affecting the upstream Kubernetes CSI drivers for NFS and SMB. These flaws, discovered in January 2026 and reported through coordinated disclosure, allow attackers with the privilege to create PersistentVolumes to escape intended subdirectory boundaries. This escape can lead to unauthorized access to data belonging to other tenants sharing the same storage export.
The vulnerabilities stem from a misunderstanding of how the filepath.Join function in Go operates. Contrary to a common misconception, filepath.Join is a path normalizer, not a security boundary. It collapses elements like . and .. into a canonical form without any awareness of a base directory. This means that when a crafted volume identifier is processed, the function can return a path outside the intended scope, such as /etc/passwd, even though the path appears clean.
In typical deployments where multiple tenants share a single NFS or SMB export, each tenant is assigned a dedicated subdirectory. The CSI drivers assume that the subDir component within the volumeHandle field of a PersistentVolume correctly isolates each tenant. However, the path traversal flaws allow an attacker to manipulate this subDir to navigate outside their designated area and access or modify files in other tenants' subdirectories.
The impact of these vulnerabilities is significant. In default configurations, attackers can read, modify, and delete files belonging to other tenants. A more severe scenario arises when CSI controllers are configured with broader hostPath mounts, a common practice for log collection or operational tooling. In such cases, the path traversal can target critical system directories on the Kubernetes worker node, including paths like /var/lib/kubelet, /etc/kubernetes, or /etc/cni. Deleting these essential directories can lead to node destruction and widespread service disruption.
The Kubernetes Security Response Committee has assigned CVE-2026-3864 to the NFS driver vulnerability and CVE-2026-3865 to the SMB driver vulnerability. The Kubernetes CSI drivers for NFS and SMB are maintained by the upstream kubernetes-csi organization. Fixes for these issues have been released in csi-driver-nfs version v4.13.1 and csi-driver-smb version v1.20.1.
The practical exploitability of these vulnerabilities is amplified by the common practice of granting persistentvolumes:create permissions to automated systems like CI/CD pipelines, ArgoCD, and Helm. While the documented threat model for Kubernetes storage often assumes this permission is held only by cluster administrators, its widespread delegation means that compromising these automated services can provide attackers with the necessary privileges to exploit these path traversal flaws.
This situation highlights a recurring theme in containerized storage security: the reliance on insecure assumptions about path manipulation functions. The vulnerability underscores the importance of using security-hardened path joining functions, such as filepath-securejoin in Go, which are designed to prevent escapes from designated base directories and are aware of symbolic links, rather than relying on general-purpose path normalizers.