CVE-2026-122318
Description
A flaw was found in Kyverno. This vulnerability allows an attacker possessing a certificate issued by a trusted private authority to bypass image verification policies. By omitting the Subject Alternative Name (SAN) from a signing certificate, identity checks on image signers are skipped during policy evaluation. Consequently, an attacker can deploy unauthorized or malicious container images into the cluster despite configured signer restrictions.
Statement
This vulnerability is rated Important because a successful bypass directly undermines Kubernetes admission security controls by permitting unauthorized container workloads to execute in the cluster. While exploitation requires low-privileged access to obtain a certificate issued under a configured trust chain, the resulting breakdown of supply chain integrity allows arbitrary image admission across impacted namespaces. Clusters that do not utilize Kyverno for image signature validation or that do not enforce subject-based constraints are not impacted.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
--- CME Mitigation Guidance (2026-11-06) ---
Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.
The highest-value action is to enforce signer identity checks within Kyverno image verification policies regardless of whether Subject Alternative Names are present on signing certificates: upgrade to Kyverno 1.19.2 (or the corresponding fixed Red Hat builds), which enforce subject and subjectRegExp validation checks even when Subject Alternative Names are absent from the signing certificate, closing all 2 injection vectors (SAN-less leaf certificate signing, Fulcio issuer OID spoofing in certificates without SAN). Until patched, this is only a concern on Kubernetes clusters running Kyverno classic cosign verifyImages policies enforcing subject or subjectRegExp constraints — Clusters not using Kyverno for image signature validation, policies without subject constraints, or CEL ivpol verifiers are unaffected — so Restrict private CA certificate issuance to forbid leaf certificates lacking Subject Alternative Names, and strictly control workload deployment privileges across cluster namespaces. As a compensating measure, Enforce container image signature and provenance verification through independent verification tooling such as Sigstore Policy Controller or CI/CD gates to validate signer identity and block unverified images and Enforce default-deny validation across certificate attributes to prevent Kyverno from failing open and skipping signer identity checks when Subject Alternative Names are omitted. These controls limit blast radius and contain exploitation, but they do not fix the underlying improper certificate validation defect — apply the upstream patch to fully remediate.
Highest-impact CME: CME-712 Container Image Signing and Provenance Verification (Cosign/Sigstore) (medium)
Understanding the Weakness (CWE)
Integrity,Authentication
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity
When a certificate is invalid or malicious, it might allow an attacker to spoof a trusted entity by interfering in the communication path between the host and client. The product might connect to a malicious host while believing it is a trusted host, or the product might be deceived into accepting spoofed data that appears to originate from a trusted host.
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