CVE-2026-122318 in Kyverno
Summary
by MITRE • 11/05/2026
Kyverno before 1.19.2 contains an authentication bypass in matchCertificateData that skips verifyImages subject and subjectRegExp checks when the signing certificate has no Subject Alternative Name. Attackers holding a leaf certificate from a configured private trust root can omit the SAN, set the expected Fulcio issuer OID, and sign malicious images that are admitted despite signer pinning.
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Analysis
by VulDB Data Team • 11/05/2026
The vulnerability identified in Kyverno versions prior to 1.19.2 represents a critical authentication bypass within its image verification policy engine, specifically affecting the matchCertificateData function used for validating container signatures against trusted certificate authorities. This flaw stems from an incomplete implementation of X.509 certificate validation logic when processing certificates that lack Subject Alternative Name extensions. In standard PKI practices and modern security frameworks such as those defined by NIST SP 800-193, the Subject Alternative Name extension is often preferred over the Common Name field for identifying entities due to its flexibility and support for multiple identifiers including DNS names, IP addresses, and URIs. Kyverno’s verification process was designed to enforce strict checks on both the subject field and regular expression patterns defined in policy rules to ensure that only images signed by authorized identities are admitted into a cluster. However, when an attacker presents a leaf certificate issued by a configured private trust root but deliberately omits the Subject Alternative Name extension, the validation logic fails to properly evaluate the expected Fulcio issuer Object Identifier or other subject-based constraints. This oversight allows maliciously crafted container images to bypass signer pinning mechanisms and be accepted as legitimate despite not meeting the intended security criteria.
From an operational perspective, this vulnerability enables attackers who possess a leaf certificate from any private trust root configured within the Kyverno policy namespace to inject untrusted code into Kubernetes workloads. By exploiting the absence of SAN validation, adversaries can sign arbitrary container images using certificates that appear valid under basic chain-of-trust checks but fail deeper semantic verification required by secure supply chain standards like SLSA or CISA’s Secure Software Development Framework. The impact is severe because it undermines the integrity guarantees provided by image signing policies, potentially leading to privilege escalation, data exfiltration, or lateral movement within the cluster if the compromised images contain malicious payloads. This aligns with ATT&CK technique T1608 which involves weaponizing legitimate software features for unauthorized access and reflects CWE-295 regarding improper certificate validation where critical fields are not adequately checked during authentication processes.
Mitigation strategies must prioritize immediate upgrading to Kyverno version 1.19.2 or later where the logic has been corrected to enforce strict adherence to X.509 standards regardless of whether Subject Alternative Name extensions are present in the presented certificates. Organizations should also audit their existing image signing policies to ensure they do not rely solely on Common Name fields for identity verification, as this field is deprecated and prone to ambiguity according to RFC 5280 best current practices. Implementing additional layers of defense such as runtime security monitoring using tools like Falco or Sysdig can help detect anomalous behavior resulting from compromised images even if the initial admission control fails. Furthermore, adopting a zero-trust architecture for container registries and enforcing mutual TLS with strict certificate validation policies will reduce the attack surface available to adversaries attempting to exploit similar weaknesses in other components of the cloud-native stack. Regular vulnerability scanning and penetration testing focused on PKI implementations within CI/CD pipelines are essential to maintain resilience against evolving threats targeting supply chain integrity mechanisms.