With the correct privileges an attacker can use the Kubernetes API to modify certain properties of an existing pod and achieve code execution within the pod
|PermissionSet||Pod||Lateral Movement, TA0008|
kubectl patch command enables updating specific fields of a resource, including pods. However, the fields that can be updated using a
PATCH command depend on the resource's API schema and the specific Kubernetes version in use. In the current version (1.27) only a very restricted set of fields can be modified using this command:
spec.tolerations (only additions to existing tolerations)
spec.terminationGracePeriodSeconds (allow it to be set to 1 if it was previously negative)
However, this is still just enough to allow an attacker to achieve execution in a pod by modifying the container image of a running pod to a backdoored container image in an accessible container registry.
Ability to interrogate the K8s API with a role allowing pod patch access.
See the example pod spec.
Simply ask kubectl:
First, create a backdoored container image and save in an accessible container registry. For demonstration purposes we will use
kalilinux/kali-last-release in dockerhub. Next create a patch file, changing the target pod image to our backdoored image:
Finally apply the patch via
If trusted container registries are enforced, a different approach is required. There are two options: + Introduce an attacker-controlled container into the trusted registry (mechanisms for this are out of scope). This approach may or may not be possible depending on the level of access, but is the simplest option if an attacker already has appropriate access. + Find an image in the trusted registry with a known vulnerability that can be exploited to achieve RCE.
Enforce Usage of Trusted Container Registries
Prevent pods pulling images from non-trusted container registries. Since the
pod/patch access is limited to modifying the container image, blocking access to untrusted registries makes this attack significantly harder to achieve (requires introducing a malicious image into a trusted regsitry).
Implement least privilege access
Pod patch is a very powerful privilege and should not be required by the majority of users. Use an automated tool such a KubeHound to search for any risky permissions and users in the cluster and look to eliminate them.