Cases3 cases

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1. IL-0053 Unauthenticated ingress-nginx admission webhook let anyone on the pod network run code and read every Secret in the cluster (IngressNightmare, CVE-2025-1974)

   Wiz2025

   Symptoms

   This is a vulnerability report, not an outage, so nothing failed visibly. A cluster is exposed if it runs Ingress NGINX Controller older than 1.12.1 or 1.11.5 with its validating admission webhook enabled. Wiz suggests `kubectl get pods --all-namespaces --selector app.kubernetes.io/name=ingress-nginx` to find it. The webhook accepts AdmissionReview requests over HTTP without authentication from any pod, and Wiz found more than 6,500 clusters exposing it to the public internet.

   Unauthorised access or a foreign workload

   Trigger

   Wiz Research reviewed the code of the Ingress NGINX admission controller and reported the first findings to Kubernetes on 31 December 2024.

   Root cause

   Software defect

   Component

   Ingress controllerAdmission webhook

   Contributing factor

   Unreviewed defaultsExcessive blast radius

   Detection

   Found by Wiz Research in a code review of the admission controller, not by an operator.

   Remediation

   • Kubernetes patched the injection flaws CVE-2025-1097, CVE-2025-1098 and CVE-2025-24514
   • Kubernetes removed NGINX configuration testing from the ingress-nginx admission controller, resolving CVE-2025-1974
   • released Ingress NGINX Controller 1.12.1 and 1.11.5

   Lessons

   Admission webhooks often run as web servers inside the cluster without authentication and with relatively high privileges, so any pod can reach them, and the flaws pair well with SSRF in an application. Wiz concludes that `nginx -t` should be considered harmful when it processes unsanitized user input. Wiz recommends upgrading, keeping the webhook off the internet and allowing only the API server to reach it with network policies. If upgrading must wait, disable the webhook (Helm: controller.admissionWebhooks.enabled=false; manual installs: delete the ValidatingWebhookConfiguration ingress-nginx-admission and remove --validating-webhook from the controller) and enable it again after the upgrade.

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2. IL-0008 An unresponsive OPA validating webhook crash-looped the API server during a GKE master upgrade, and node auto-repair then recreated every node

   Jetstack2019

   Symptoms

   Jetstack was upgrading the master of a development cluster that many teams use to test their apps during the working day, a regional Google Kubernetes Engine (GKE) cluster in europe-west1. The upgrade ran through Jetstack's GKE Terraform pipeline and did not finish before the 20-minute Terraform timeout, while the GKE console still showed the cluster as upgrading.

   Upgrade stallControl plane unresponsiveNode recreation loopService outage

   Trigger

   A planned master upgrade of the shared development cluster. The same upgrade had been done on another pre-production environment earlier that day, and no API downtime was expected.

   Root cause

   Configuration change

   Component

   Admission webhookGKE control planeKubernetes API serverkubelet

   Contributing factor

   Excessive blast radiusNo health probesMonitoring blind spotAutomation amplification

   Detection

   The first sign was the master upgrade missing the 20-minute Terraform timeout; re-running the pipeline returned the kube-apiserver unhealthy error. The cause was identified with the help of Google Support.

   Remediation

   • Deleted the OPA ValidatingAdmissionWebhook resource during a window of API server access

   Action items

   • Limit the OPA webhook to the namespaces where the policy applies and development teams have access
   • Enable the webhook only for Ingress and Service resources, the only resources the policy validates
   • Add a liveness probe so OPA is restarted when it stops responding, and update the OPA documentation
   • Follow the open upstream Kubernetes issue about this behaviour

   Lessons

   With alerting on API server response times, the team might have seen CREATE and UPDATE requests slow down across the board as soon as the OPA-backed webhook was first deployed. Every workload needs probes: OPA looked so simple to deploy that the team skipped the Helm chart, which adds a livenessProbe for the admission controller containers among other adjustments to the tutorial configuration. Others had hit the same problem, and an upstream issue to improve it was still open.

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3. IL-0037 Image registry rate-limited a whole region after a crash-looping DaemonSet with imagePullPolicy Always pulled through three NAT instances

   Datadog2019

   Symptoms

   Users reported that their jobs were not starting, with some sign that image pulls were involved. Many pods across the cluster were in error states related to image pulls, while applications that were already running were not affected.

   Image pull failuresService outage

   Trigger

   A change to the permissions on a storage bucket that one application needed to read. The application could no longer start, and its DaemonSet, running on roughly a thousand nodes of the cluster, went into a crash loop with imagePullPolicy: Always, so every restart pulled the image again although it was already on the node.

   Root cause

   Capacity exhaustion

   Component

   Container registry and its credentialsNAT gatewayApplication databaseAdmission webhook

   Contributing factor

   Automation amplificationSingle point of failureUnknown limitHarmful manual actionExcessive blast radius

   Detection

   Users reported that their jobs were not starting; monitoring had not caught it first.

   Remediation

   • replaced the affected NAT instances so registry traffic came from new source IPs
   • reconfigured the static IPs and firewall rules so applications could reach the Cloud SQL database again

   Action items

   • Add an admission webhook that rejects floating image tags, starting with latest
   • Apply the image tag webhook to workload objects only, not to pods, after it blocked pods created by in-cluster controllers

   Lessons

   The speakers' takeaway is to be very careful with DaemonSets in large clusters: they say they had broken everything DaemonSets depend on, including DNS, Vault and the image repository, and that it is very easy to break things when managing them by the thousand. imagePullPolicy: Always made every crash-loop restart pull the image again. Sending all registry traffic through three NAT instances put the whole region behind three source IPs, which the registry rate-limited, and changing those IPs cut the connections to a critical database reached over the internet through them. An admission webhook on pods rejects the pods that controllers in the cluster create, where no user sees the error.

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