Description

Kyverno versions v1.9.0 through v1.12.7 contain a policy exception handling flaw. When a policy in enforce mode is combined with two PolicyExceptions, the less restrictive exception takes precedence, allowing an attacker to bypass the policy by crafting a resource name that matches the second exception's name pattern (e.g., '*ingress*'). This can be used to circumvent policies such as one blocking hostPath volumes. Fixed in v1.13.0.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.0",
  "pubDate": "2026-09-01T12:17:49.540Z",
  "pubdate": "2026-09-01T12:17:49.540Z",
  "executiveSummary": "Kyverno versions v1.9.0 through v1.12.7 are affected by a security flaw within the policy exception handling mechanism. The vulnerability involves improper evaluation logic when multiple PolicyExceptions are present for a single policy in enforce mode.\nThis flaw allows an attacker to bypass security constraints—such as prohibitions against hostPath volumes—by manipulating resource names to align with less restrictive exception patterns. The vulnerability stems from an incorrect precedence hierarchy where a weaker exception can override more stringent policy enforcement.\nSuccessful exploitation allows unauthorized resources or configurations that should otherwise be blocked to persist within the Kubernetes cluster. This effectively invalidates the security posture defined by the cluster administrator. The risk is high, as it enables the circumvention of established guardrails without requiring elevated privileges beyond the ability to create or modify Kubernetes resources. This vulnerability was addressed and resolved in Kyverno v1.13.0.",
  "technicalDetails": "The vulnerability resides within the Kyverno admission controller's evaluation engine, specifically in how the PolicyException object interacts with policies configured in 'enforce' mode. When a cluster administrator defines multiple exceptions to a single policy, the Kyverno engine is expected to evaluate these exceptions to determine if the incoming resource request should be exempt from the enforced rule.\nThe root cause is a logic error in the precedence evaluation algorithm. In the vulnerable versions, the engine fails to correctly aggregate or apply the most restrictive match criteria when multiple PolicyException objects are applicable. Instead, the logic inadvertently allows the less restrictive exception to take precedence over more restrictive ones.\nThe attack flow proceeds as follows: An attacker identifies a target Kubernetes policy that is set to enforce mode (e.g., a policy preventing hostPath volume mounts). The attacker discovers that the policy has multiple PolicyException objects configured for various resources. By crafting a new resource—such as a Pod or Ingress—with a name that matches the wildcard pattern defined in a broad or 'less restrictive' exception (e.g., '*ingress*'), the attacker triggers the flawed evaluation logic. Because the engine incorrectly prioritizes this broad exception, the Kyverno controller validates the malicious resource as compliant, effectively bypassing the security control.\nThis vulnerability is particularly impactful because it does not require external network access or complex exploit chains; it is a logic flaw inherent in the admission request lifecycle. An attacker with the standard permissions to create resources within a namespace can leverage this flaw to circumvent infrastructure-level policies, leading to potential privilege escalation or security policy violation. The issue persists until the engine performs an evaluation, and because the flaw is in the decision-making logic of the controller itself, it consistently permits the unauthorized operation throughout the vulnerable version range of v1.9.0 to v1.12.7.\nThe vulnerability is limited to the logic governing PolicyException processing within the Kyverno engine and does not require the attacker to have administrative control over the Kyverno installation itself, provided they can influence the creation of resources subject to the bypassed policies."
}