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kubernetes

API server pod has DenyServiceExternalIPs admission controller enabled

apiserver_deny_service_external_ips
Service: apiserverSeverity: high
OfficialBuilt-inVerified
Categories:cluster-securitytrust-boundariesinternet-exposed
Resource Type:Pod

Kubernetes API server with DenyServiceExternalIPs rejects net-new use of Service.spec.externalIPs and additions to that field on existing Services; existing values can only be removed.

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Risk

Without DenyServiceExternalIPs, users with Service create/patch rights can reroute traffic via arbitrary external IPs, enabling man-in-the-middle, traffic hijacking, and data exfiltration, degrading confidentiality and integrity. Attackers may also abuse status.loadBalancer.ingress.ip to similar effect.

Run this check with Prowler

Run in Prowler Cloud
Run
prowler kubernetes --checks apiserver_deny_service_external_ips

Recommendation

Enable DenyServiceExternalIPs to block net-new externalIPs usage.

Apply least privilege RBAC on Services (including status updates), require change control for exposure, and favor controlled Ingress/LoadBalancer patterns. Use admission policies to tightly allow approved exceptions as defense in depth.

Remediation

Other

1SSH to the control plane node
2Edit /etc/kubernetes/manifests/kube-apiserver.yaml
3In the kube-apiserver command/args list, add: --disable-admission-plugins=DenyServiceExternalIPs
4Save the file; the kubelet will restart the API server automatically

Check Code

from prowler.lib.check.models import Check, Check_Report_Kubernetes
from prowler.providers.kubernetes.services.apiserver.apiserver_client import (
    apiserver_client,
)


class apiserver_deny_service_external_ips(Check):
    def execute(self) -> Check_Report_Kubernetes:
        findings = []
        for pod in apiserver_client.apiserver_pods:
            report = Check_Report_Kubernetes(metadata=self.metadata(), resource=pod)
            report.status = "PASS"
            report.status_extended = f"API Server has DenyServiceExternalIPs admission controller enabled in pod {pod.name}."
            deny_service_external_ips = False
            for container in pod.containers.values():
                deny_service_external_ips = False
                for command in container.command:
                    if command.startswith("--disable-admission-plugins"):
                        if "DenyServiceExternalIPs" in (command.split("=")[1]):
                            deny_service_external_ips = True
                if not deny_service_external_ips:
                    break
            if not deny_service_external_ips:
                report.status = "FAIL"
                report.status_extended = f"API Server does not have DenyServiceExternalIPs enabled in pod {pod.name}."
            findings.append(report)
        return findings

References