Kyverno EUVD-2026-87679

Requires an authenticated Kubernetes namespace tenant with the ability to define or trigger a Kyverno Policy that uses the apiCall feature with a controllable urlPath (PR:L). Exploitation depends on Kyverno versions before 1.19.1 being deployed and on a multi-tenant model where namespace-scoped users are trusted to author policies; the attacker supplies percent-encoded directory-traversal sequences in urlPath to defeat the per-namespace clamp. No user interaction is needed. The practical limiting factor is that the attacker must already hold namespace-level policy/apiCall authoring rights - a single-tenant or admin-only cluster is not exposed to cross-tenant escalation, though the same primitive still grants cluster-wide object creation via the admission-controller ServiceAccount.

This is a genuine high-priority issue, not a high-CVSS-but-low-real-risk case. The vendor CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N with full VC/VI/VA:H and subsequent-system SC/SI/SA:H = 9.4) describes a low-complexity, network-reachable, low-privilege flaw that escalates to full cluster compromise - consistent with the CWE-441 confused-deputy mechanism where the trusted Kyverno admission-controller ServiceAccount performs the attacker's cross-namespace writes. The impact rating is credible: creating MutatingWebhookConfiguration objects cluster-wide or PolicyException objects in the kyverno namespace is a direct, well-understood path to cluster-admin. The one meaningful gate is PR:L - the attacker must already be an authenticated namespace tenant with rights to define/trigger a Policy apiCall, so this is a tenant-escaping privilege escalation rather than a fully external unauthenticated RCE. No EPSS score, no CISA KEV listing, and no public POC were provided, so there is no evidence of active exploitation; the risk here is driven by severity of impact and low exploitation complexity, not by observed in-the-wild activity. A vendor patch (1.19.1) is confirmed available, which should anchor remediation urgency for any multi-tenant cluster.

A tenant who controls a namespace with permission to author or invoke a Kyverno Policy containing an apiCall crafts a urlPath using percent-encoded directory-traversal sequences (e.g. %2e%2e%2f) that bypass Kyverno's per-namespace clamp. Kyverno, acting as its privileged admission-controller ServiceAccount, resolves the decoded path and creates a MutatingWebhookConfiguration cluster-wide or a PolicyException in the kyverno namespace, which the attacker leverages to escalate to cluster admin. No public exploit code was identified at time of analysis, but the technique is low-complexity and requires only existing tenant-level access.