Kubernetes Threat Model

Threat modeling is a structured approach that helps identify and mitigate potential security threats in a system. In the context of Kubernetes, it involves analyzing the architecture, components, and interactions within a Kubernetes cluster to identify vulnerabilities and risks.

Kubernetes Trust Boundaries and Data Flows

Trust Boundaries

Let's take a look at this diagram. The user interacts with the cluster through an ingress controller. The ingress controller routes the traffic to the frontend pod, which in turn communicates with the backend pod. The backend pod interacts with the database pod.

Now, let's say that the hacker compromises the frontend pod. The hacker can then use the compromised frontend pod to access the backend pod and potentially the database pod as well, because the diagram here does not isolate the pods and no enforce specific security measures between them.

In this diagram, we have isolated them different groups of pods and enforce specific security measures between them (Pod). So, if the hacker compromise one part of the system, they will not be able to compromise the other parts of the system.

Cluster Boundary

The cluster boundary is the boundary between the clusters in a Kubernetes setup. We know that the Kubernetes setup involves control-plane components and worker** nodes**, these items will be part of the cluster boundary. So, the best is to separate or isolate the clusters for different environments. For example, we can have a cluster for production, a cluster for development, and a cluster for testing. With this setup, we can ensure that the issues in one cluster will not affect the other clusters.

Node Boundary

The node boundary is the boundary between the nodes in a Kubernetes cluster. It ensures that the pods running on one node are isolated from the pods running on another node. For example, if a frontend pod running on node 1 is compromised, the hacker will not be able to access the backend pods running on node 2 or the database pods running on node 3. This is because the network traffic between the nodes is isolated.

Pod Boundary

The pod boundary is the boundary between the pods in a Kubernetes cluster. Each pod typically runs one or more containers. Pods are isolated from each other using its own network policies, runtime environment, and security context, as these can be defined at the pod level.

By default, pods within the same namespace or cluster can communicate freely unless network policies are explicitly applied to restrict communication.

This ensures that pods are not able to access each other unless explicitly allowed by these policies.

Namespace Boundary

The namespace boundary is the boundary between the namespaces in a Kubernetes cluster. Namespaces are used to organize and isolate resources within a cluster. Each namespace can have its own set of resources, such as pods, services, and config maps.

Container Boundary

The container boundary is the boundary between containers within a pod. Containers in the same pod share the same network namespace and can communicate with each other via localhost. It provides application-level isolation. For example, if a container in a pod is compromised, the damange is limited to that container.

Data Flows

Data flow is the movement of data between different components in a Kubernetes cluster. Understanding data flows is crucial for identifying potential vulnerabilities and attack vectors.

To protect the data flows, we can take the following measures:

• implement network policies to restrict communication between pods and namespaces
• use encryption (TLS) for data in transit and at REST
• secure the ingress and egress traffic
• implement service mesh, etc

Persistence

Persistence is the ability of a system to maintain its state and data across different attacks by hackers. In Kubernetes, hacker can achieve persistence by exploiting misconfigurations, reading secrets or using container vulnerabilities.

There are several ways to mitigate Persistence risks:

• Use RBAC to restrict access to service accounts or sensitive resources like secrets.
• Use PodSecurityPolicies to
  • prevent containers from running as root or with privileged access
  • enforce security contexts for pods and containers
  • enforce read-only root filesystem
• Regular updates and patching of container images.
• Implement monitoring and auditing of Kubernetes cluster activity to detect any suspicious activities and audit Kubernetes events regularly.
  • Track changes to RBAC policies, secrets, creation of new pods, network policies, and other security-related configurations.
  • Alert on any suspicious activities or changes to the cluster.

Denial of Service

Denial of Service (DoS) attack is an attack that aims to make a service unavailable to its intended users. In Kubernetes, DoS attacks can be achieved by overloading the cluster with requests or by exploiting vulnerabilities in the cluster components.

We know that by default pod has a service account, which is used to authenticate the pod to the API server. If the hacker compromises the pod, they can use the service account token to authenticate to the API server and start many containers or send many requests in the cluster. This can lead to resource (CPU & memory) exhaustion.

There are several ways to mitigate Denial of Service risks:

• Setup resource quota and limit range for each namespace, which will limit the number of resources that can be used by the pods in that namespace.
• Setup resource limits and requests for each pod
• Setup network policies and proper firewall configurations to protect control plane endpoints and to control traffic flow within the cluster. For example, only allow trusted IP addresses to access the API server.
• Secure service accounts using RBAC to restrict the permissions of the service accounts. For example, can limit the service account to only be able to0 read the resources in the cluster, but not to create or delete them.
• Implement monitoring and alerting for unusual traffic patterns or spikes in resource.

Malicious Code Execution

Malicious code execution is an attack that aims to execute arbitrary (malicious) code on a system. In Kubernetes, this can be achieved by exploiting vulnerabilities in the cluster components or by compromising the pods running in the cluster.

Here are the common steps to achieve this:

1. The hacker compromises a pod by exploiting a vulnerability in the application running in the pod.
2. The hacker executes malicious code in the compromised pod to install a malicious software to steal sensitive data or perform other malicious activities.
3. The hacker can poison image repository by uploading a malicious image to the repository. So if other clusters pull the image, they will be compromised as well.

apiVersion: v1
kind: Pod
metadata:
  name: example-hostpid-pod
  namespace: default
spec:
  hostPID: true
  containers:
  - name: example-container
    image: busybox
    command: ["sh", "-c", "ps aux"]

Hacker will primarily focus on finding the pod that enables hostPID and SYS_PTRACE capabilities. This is because these two features can be used to compromise the host.

If the container is running with hostPID, the hacker can access the host process, meaning that the hacker can see all the processes running on the host, interact with the host processes, and potentially compromise the host.

If the container enables SYS_PTRACE capability, the hacker can inspect the host processes and attach to them. This can be used to debug the processes or inject malicious code into the host processes.

There are several ways to mitigate Malicious Code Execution risks:

• Secure container image repositories by ensuring that only trusted images are uploaded to the repository.
  • Use image signing to ensure that the images are authentic and untampered.
• Secure image pull secrets and restrict access to only necessary pods using RBAC.
• Use PodSecurityPolicies to prevent containers from running with hostPID and SYS_PTRACE capabilities.
• Use signed images to verify the integrity of the images before deploying them to the cluster.
• Regular updates and patching of container images.

Access to sensitive data

Hacker can access to sensitive data can through multiple ways:

• One is misconfigured RBAC policies. The hacker can exploit (use) the misconfigured RBAC policies to gain access to sensitive data in the cluster.
• Second is accessing and viewing sensitive data in logs.
• Third is eavesdropping (spy) on the network traffic between the pods. The attacker can intercept the network traffic and read the sensitive data being transmitted between the pods if the network traffic is not encrypted.

There are several ways to mitigate Access to sensitive data risks:

• Ensure that RBAC policies are properly configured and restrict access to sensitive data.
• Ensure the logs do not log sensitive data. Restrict access to logs and use centralized logging solutions to provide fine-grained access control and monitor access to logs.
• Use encryption (TLS) for data in transit to protect sensitive data being transmitted between the pods.

Privilege Escalation

Privilege escalation is an attack that aims to gain elevated privileges in a system. Here is the scenario, we might want to run a command using the root user privileges.

visudo

# User privilege specification
root    ALL=(ALL:ALL) ALL
 
# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL
 
# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL
 
# See sudoers(5) for more information on "@include" directives:
 
anson   ALL=(ALL:ALL) ALL
 
# Allow KC to reboot the system
@includedir /etc/sudoers.d
kc      localhost=NOPASSWD: /sbin/reboot

Only users listed in the /etc/sudoers file can run commands with sudo. In this case, anson has complete privileges while kc can only run the /sbin/reboot command without a password.