Secure Webhook Management

A more secure way to manage Istio webhooks.

Nov 14, 2019 | By Lei Tang - Google

Istio has two webhooks: Galley and the sidecar injector. Galley validates Kubernetes resources and the sidecar injector injects sidecar containers into Istio.

By default, Galley and the sidecar injector manage their own webhook configurations. This can pose a security risk if they are compromised, for example, through buffer overflow attacks. Configuring a webhook is a highly privileged operation as a webhook may monitor and mutate all Kubernetes resources.

In the following example, the attacker compromises Galley and modifies the webhook configuration of Galley to eavesdrop on all Kubernetes secrets (the clientConfig is modified by the attacker to direct the secrets resources to a service owned by the attacker).

An example attack
An example attack

To protect against this kind of attack, Istio 1.4 introduces a new feature to securely manage webhooks using istioctl:

  1. istioctl, instead of Galley and the sidecar injector, manage the webhook configurations. Galley and the sidecar injector are de-privileged so even if they are compromised, they will not be able to alter the webhook configurations.

  2. Before configuring a webhook, istioctl will verify the webhook server is up and that the certificate chain used by the webhook server is valid. This reduces the errors that can occur before a server is ready or if a server has invalid certificates.

To try this new feature, refer to the Istio webhook management task.