CVE-2026-122306 in Kyverno
Summary
by MITRE • 11/05/2026
Kyverno before 1.19.2 contains a denial of service vulnerability that allows namespaced policy authors to exhaust admission controller CPU by submitting pathological wildcard patterns. Attackers can create a Policy with crafted match and exclude names evaluated by ValidateMatchExcludeConflict, pinning cores and causing cluster-wide webhook timeouts that block resource operations.
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Analysis
by VulDB Data Team • 11/05/2026
The identified security flaw resides within Kyverno versions prior to 1.19.2 and represents a critical denial of service vulnerability affecting the admission controller subsystem. This issue specifically impacts namespaced policy authors who possess the ability to create or modify policies within their designated namespaces. The core technical deficiency lies in how the system processes wildcard patterns during the evaluation phase, particularly when interacting with the ValidateMatchExcludeConflict logic. When an attacker submits a policy containing crafted pathological wildcard patterns, the admission controller is forced into an inefficient computational state that consumes excessive CPU resources. This behavior stems from the algorithmic complexity involved in matching and excluding resource specifications against broad or ambiguous wildcards, which can lead to exponential time complexity depending on the cluster's scale and configuration.
The operational impact of this vulnerability is severe for Kubernetes clusters relying on Kyverno for policy enforcement. By submitting these maliciously crafted policies, an attacker can effectively pin CPU cores dedicated to the admission controller process. This resource exhaustion leads directly to cluster-wide webhook timeouts, as the system becomes unable to respond within the expected timeframes required by the Kubernetes API server. Consequently, legitimate resource operations such as pod creation, deployment updates, or configuration changes are blocked because the admission control step fails to complete in a timely manner. This results in a significant degradation of service availability and can effectively halt normal cluster operations until the offending policy is removed or the Kyverno controller is restarted.
From a classification perspective, this vulnerability aligns with CWE-400, which covers uncontrolled resource consumption leading to denial of service conditions. The attack vector leverages the legitimate functionality of policy matching but abuses it through pathological inputs that trigger inefficient processing paths. In terms of adversarial tactics, this behavior corresponds to ATT&CK technique T1496, specifically Resource Hijacking or Denial of Service via computational exhaustion within a containerized environment. It highlights the risk associated with allowing users to define complex matching rules without sufficient safeguards against computationally expensive patterns that can destabilize shared infrastructure components like admission controllers.
To mitigate this vulnerability, organizations must immediately upgrade Kyverno to version 1.19.2 or later where these issues have been addressed through optimized pattern matching algorithms and stricter validation limits on wildcard complexity. In the interim, administrators should enforce strict RBAC policies to limit which users can create or modify cluster-wide or namespaced policies that involve complex match criteria. Additionally, implementing resource quotas for the admission controller pods can help contain the impact of such attacks by preventing a single process from consuming all available CPU resources in the node pool. Regular auditing of policy definitions and restricting the use of broad wildcards in production environments are also recommended defensive measures to reduce the attack surface associated with this type of computational exhaustion flaw.