CVE-2024-48921 in Kyverno
Summary
by MITRE • 10/29/2024
Kyverno is a policy engine designed for Kubernetes. A kyverno ClusterPolicy, ie. "disallow-privileged-containers," can be overridden by the creation of a PolicyException in a random namespace. By design, PolicyExceptions are consumed from any namespace. Administrators may not recognize that this allows users with privileges to non-kyverno namespaces to create exceptions. This vulnerability is fixed in 1.13.0.
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Analysis
by VulDB Data Team • 11/06/2024
The vulnerability identified as CVE-2024-48921 affects Kyverno, a popular policy engine for Kubernetes environments that enforces security policies across containerized workloads. This issue stems from a design flaw in how Kyverno handles PolicyExceptions within its ClusterPolicy framework, specifically with the "disallow-privileged-containers" policy. The core problem lies in the unrestricted consumption of PolicyExceptions from any namespace within the cluster, which fundamentally undermines the security posture that administrators expect from centralized policy enforcement mechanisms. When a ClusterPolicy is configured to disallow privileged containers, the system should maintain strict enforcement regardless of user privileges or namespace boundaries, yet this vulnerability creates an unintended bypass mechanism.
The technical flaw manifests when users with permissions to create resources in any namespace can establish PolicyExceptions that effectively override the centralized ClusterPolicy enforcement. This behavior represents a critical access control violation where the principle of least privilege is compromised, allowing potentially malicious actors or unauthorized users to circumvent security controls simply by creating resources in namespaces they control. The vulnerability specifically impacts the "disallow-privileged-containers" policy, which is fundamental to preventing containers from running with elevated privileges that could lead to privilege escalation attacks. This flaw directly relates to CWE-284, which addresses improper access control, and demonstrates how insufficient namespace isolation can lead to security policy bypasses. The issue is particularly concerning in multi-tenant Kubernetes environments where different teams or users may have varying levels of access but should not be able to override cluster-wide security policies.
Operationally, this vulnerability creates a significant risk for Kubernetes administrators who rely on Kyverno to maintain consistent security policies across their clusters. The impact extends beyond simple policy enforcement failure to potentially enable privilege escalation attacks, where unauthorized users could deploy privileged containers that might compromise the entire cluster. Attackers could exploit this vulnerability by simply creating a PolicyException in any namespace they have access to, effectively neutralizing the security controls that were intended to prevent privileged container execution. This vulnerability aligns with ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation," as it allows for the bypass of system-level security controls. The risk is compounded by the fact that administrators may not immediately recognize that PolicyExceptions can be created in any namespace, leading to delayed detection and remediation of security breaches.
The fix for CVE-2024-48921 requires upgrading to Kyverno version 1.13.0, which implements proper namespace isolation for PolicyException consumption. This update ensures that PolicyExceptions can only be consumed from specific, authorized namespaces rather than any namespace within the cluster. Organizations should immediately implement this upgrade as a priority to restore proper policy enforcement. Additionally, administrators should review their existing PolicyExceptions to ensure no unauthorized overrides have been introduced, and consider implementing more granular access controls for namespace creation and modification. The vulnerability highlights the importance of proper privilege management and the need for security controls to be implemented at the cluster level rather than relying on namespace-based isolation alone. Security teams should also monitor for potential exploitation attempts by watching for unexpected PolicyException creation patterns and ensure that monitoring systems are configured to alert on such activities.