CVE-2023-39347 in Cilium
Summary
by MITRE • 09/27/2023
Cilium is a networking, observability, and security solution with an eBPF-based dataplane. An attacker with the ability to update pod labels can cause Cilium to apply incorrect network policies. This issue arises due to the fact that on pod update, Cilium incorrectly uses user-provided pod labels to select the policies which apply to the workload in question. This can affect Cilium network policies that use the namespace, service account or cluster constructs to restrict traffic, Cilium clusterwide network policies that use Cilium namespace labels to select the Pod and Kubernetes network policies. Non-existent construct names can be provided, which bypass all network policies applicable to the construct. For example, providing a pod with a non-existent namespace as the value of the `io.kubernetes.pod.namespace` label results in none of the namespaced CiliumNetworkPolicies applying to the pod in question. This attack requires the attacker to have Kubernetes API Server access, as described in the Cilium Threat Model. This issue has been resolved in: Cilium versions 1.14.2, 1.13.7, and 1.12.14. Users are advised to upgrade. As a workaround an admission webhook can be used to prevent pod label updates to the `k8s:io.kubernetes.pod.namespace` and `io.cilium.k8s.policy.*` keys.
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Analysis
by VulDB Data Team • 10/19/2023
The vulnerability described in CVE-2023-39347 represents a critical authorization bypass flaw within the Cilium networking and security solution that leverages eBPF for its data plane operations. This issue stems from improper validation of pod labels during pod update operations, creating a scenario where malicious actors can manipulate network policy enforcement through crafted label values. The vulnerability specifically affects Cilium's ability to correctly identify and apply network policies based on namespace, service account, or cluster constructs, fundamentally undermining the security boundaries that these policies are designed to enforce.
The technical flaw manifests when Cilium processes pod updates and incorrectly relies on user-provided pod labels to determine which network policies should be applied to a given workload. This behavior creates a path for privilege escalation where an attacker with sufficient permissions to modify pod labels can inject malicious values that cause Cilium to bypass policy enforcement entirely. The vulnerability is particularly dangerous because it affects multiple policy types including Cilium network policies, Cilium clusterwide network policies, and standard Kubernetes network policies, creating widespread impact across the entire network security posture. When non-existent namespace values are provided through the `io.kubernetes.pod.namespace` label, the system fails to apply any namespaced policies, effectively rendering the security controls useless for that particular pod.
From an operational impact perspective, this vulnerability creates a significant risk to containerized environments relying on Cilium for network segmentation and traffic control. The attack requires access to the Kubernetes API server, aligning with the Cilium threat model and indicating that the vulnerability is not a direct network attack vector but rather a privilege escalation issue within the Kubernetes cluster itself. The flaw allows attackers to bypass network policies that are meant to restrict traffic between namespaces, service accounts, and cluster components, potentially enabling lateral movement and data exfiltration attacks. This vulnerability directly maps to CWE-284 (Improper Access Control) and represents a failure in input validation and access control mechanisms within the Cilium system.
The mitigation strategy involves upgrading to Cilium versions 1.14.2, 1.13.7, or 1.12.14, which contain the necessary patches to address the label validation issue. Organizations without immediate upgrade capabilities can implement an admission webhook as a temporary workaround to prevent updates to critical pod labels including `k8s:io.kubernetes.pod.namespace` and `io.cilium.k8s.policy.*` keys. This approach aligns with ATT&CK technique T1078.004 (Valid Accounts: Cloud Accounts) and T1566.001 (Phishing: Spearphishing Attachment) as it addresses the privilege escalation path that could be exploited by attackers who gain access to the Kubernetes API server. The vulnerability demonstrates how seemingly minor input validation issues in security-critical components can lead to complete bypass of network security controls, emphasizing the importance of proper access control validation and the principle of least privilege in Kubernetes environments. The fix implemented in the patched versions ensures that Cilium properly validates label values before applying network policies, preventing malicious label manipulation from affecting security enforcement decisions.