CVE-2019-11247 in Kubernetes
Summary
by MITRE
The Kubernetes kube-apiserver mistakenly allows access to a cluster-scoped custom resource if the request is made as if the resource were namespaced. Authorizations for the resource accessed in this manner are enforced using roles and role bindings within the namespace, meaning that a user with access only to a resource in one namespace could create, view update or delete the cluster-scoped resource (according to their namespace role privileges). Kubernetes affected versions include versions prior to 1.13.9, versions prior to 1.14.5, versions prior to 1.15.2, and versions 1.7, 1.8, 1.9, 1.10, 1.11, 1.12.
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Analysis
by VulDB Data Team • 12/07/2023
The CVE-2019-11247 vulnerability represents a critical authorization bypass flaw in the Kubernetes kube-apiserver component that fundamentally undermines the security model of cluster resources. This vulnerability stems from a misclassification error in the API server's access control enforcement mechanism where cluster-scoped custom resources are incorrectly evaluated against namespace-specific authorization rules rather than cluster-wide permissions. The flaw exists in the authorization logic that processes requests for cluster-scoped resources when those requests are malformed to appear as namespace-scoped operations, creating a dangerous privilege escalation vector that directly violates Kubernetes' fundamental security boundaries.
The technical implementation of this vulnerability occurs at the authorization decision point within the kube-apiserver where the system fails to properly distinguish between cluster-scoped and namespace-scoped resource access patterns. When a malicious user submits a request that incorrectly identifies a cluster-scoped resource as if it were namespaced, the authorization system incorrectly enforces permissions based on namespace-level role bindings and role bindings rather than the appropriate cluster-level access controls. This misclassification allows attackers to leverage their namespace-level privileges to perform operations on cluster-scoped resources that should require cluster-admin level permissions. The vulnerability manifests in the authorization decision-making process where the system incorrectly routes the access control check through the namespace authorization path instead of the cluster authorization path, effectively bypassing the proper security boundaries.
The operational impact of this vulnerability is severe and far-reaching for Kubernetes environments, as it enables attackers with minimal privileges in a single namespace to gain unauthorized access to critical cluster resources that should be restricted to cluster administrators. An attacker with read access to a single namespace could potentially escalate their privileges to create, read, update, or delete cluster-scoped custom resources, effectively breaking the isolation guarantees that Kubernetes provides between namespaces. This vulnerability particularly affects environments where multiple teams or users share a single cluster, as it allows lateral movement and privilege escalation without requiring the attacker to first gain cluster-admin privileges. The risk is compounded by the fact that this vulnerability affects multiple Kubernetes versions, making it widespread across many production environments that may not have been properly updated.
Organizations affected by this vulnerability should immediately implement mitigations including updating to patched versions of Kubernetes where available, as the vulnerability affects versions prior to 1.13.9, 1.14.5, 1.15.2, and includes older versions 1.7 through 1.12. The recommended remediation strategy involves implementing strict access control policies that limit the ability of namespace users to access cluster-scoped resources through any means, including disabling unnecessary custom resource definitions that might be vulnerable. Security teams should also implement monitoring and alerting for anomalous access patterns that might indicate exploitation attempts, particularly around cluster-scoped resource access from namespace-scoped requests. Additionally, organizations should conduct thorough audits of their custom resource definitions and access control policies to ensure that no other similar authorization bypass vulnerabilities exist within their Kubernetes environments. This vulnerability aligns with CWE-284, which addresses improper access control, and maps to ATT&CK technique T1078 for valid accounts and privilege escalation through unauthorized access to cluster resources. The vulnerability demonstrates the critical importance of proper authorization boundary enforcement in container orchestration platforms and serves as a reminder of the need for comprehensive security testing of access control mechanisms in complex distributed systems.