Guest post originally published on Magalix’s blog by Andrew Zola

Kubernetes is a leader in container orchestration. According to Statista, as much as 46% of respondents in a recent survey stated that they used Kubernetes for automating computer application deployments, management, and scaling.

However, there are some security issues that we need to address during the container lifecycle phase. This means that you should take steps to mitigate the risk of known vulnerabilities, including misconfigurations, during the development and deployment phase. You should also be well-placed to quickly respond to potential threats during runtime.

As such, organizations need to take an in-depth look at the K8s Attack Tree and documentation. It’s important as the attack tree is essentially a threat model that offers a detailed view of potential threats and mitigations.  

You can even use this threat model as a checklist to identify potential vulnerabilities and common attack vectors a bad actor might leverage to breach the system. You can also use it as a tool to test Kubernetes security and gain visibility into the logging output that’s generated in the event of a security incident.

However, it’s important to note that the Attack Tree only focuses on Kubernetes and not end-to-end container security. This means that it doesn’t include any other application or components you may have added during the software development lifecycle.

So, whenever you plan to use Kubernetes in production, you must also consider the system’s overall security. According to the National Security Agency (NSA), common security threats include insider threats, malicious threat actors, and supply chain risks.

This makes it vital to establish Kubernetes’ security best practices from the beginning to better secure critical areas of cloud infrastructure and cloud-native environments.

Types of Kubernetes Attackers

When it comes to Kubernetes attack vectors, there are three main types—external attackers, malicious containers, and compromised or malicious users.

1- External Attackers

You can have threat actors who have no access to the cluster but are able to reach the application running on it. They might also have access to the management ports on the network.

To avoid exposure to untrusted networks, you must also be alert to controls like management services. In this case, it can take the form of networks without any form of authentication protocol.

2- Malicious Containers

If a threat actor manages to breach a single container, they will attempt to increase their access and take over the entire cluster. If there are only minimal controls to stop attackers from gaining full cluster administration rights, they will probably be successful.

To mitigate risk, you must ensure that all management ports are visible on the cluster network. You must also leverage multi-factor authentication protocols for all users. You must also avoid mounting service accounts in containers or have restricted rights.

Through network policies and using policy-as-code, you can restrict access between pods and namespaces.

3- Compromised or Malicious Users

When you’re dealing with compromised accounts or malicious users, an attacker with stolen yet valid credentials will execute commands against network access and the Kubernetes API. However, you can mitigate this risk by following a “least privilege” policy. You should also enforce Role-based Access Control (RABC) policies and best practices for all users.

The Main Attack Vectors

Last year, the CNCF Financial User Group released a threat modeling exercise that targeted a generic Kubernetes cluster. The primary objective here was to offer a detailed view of potential threats and mitigations. The accompanying checklist helps teams identify common vulnerabilities and exploits within a Kubernetes cluster.

Kubernetes Trust Boundaries – Courtesy of CNCF

Using STRIDE methodology, they analyzed each element of the Kubernetes architecture and formulated a list of potential security issues within the platform. STRIDE is an acronym that stands for Spoofing identity, Tampering with data, Repudiation threats, Information disclosure, Denial of Service, and Elevation of privileges.

Some of the main attack vectors include:

Service Token

Service tokens are mounted onto each pod by default. In this scenario, if an attacker manages to compromise a container, they will have the mechanism to exploit it further using those same credentials.

To mitigate this risk, it’s crucial to establish strict RBAC policies. It’s also essential to disable automatic service token mounting protocols.

Compromised Containers

One of the primary focal points for an attacker is the remote execution point within the cluster. Besides service token attacks, other attack vectors include the default network exposure of the control pane of all running containers.

Network Endpoints

You must secure each Kubernetes endpoint from internal threat actors. This approach helps avert an easy attack vector from being exploited. It’s crucial to note that whenever an attacker manages to compromise a container, they quickly gain access to the endpoints whenever the pods’ network policies permit it.

Denial of Service (DOS)

There were relatively few mitigations against DoS attacks before the 1.14 release.

RBAC Issues

Threat actors depend on RBAC misconfigurations to initiate a data breach. To mitigate risk, development teams must leverage automated tooling to verify and validate policies.

Attack Trees

The CNCF Financial User Group came up with a set of attack trees that could potentially determine the lineage of the initial attempt to create a foothold within the cluster. In this case, the working group came up with two approaches:

  1. Bottom-up approach.
  2. Scenario approach.

Bottom-Up Approach

The bottom-up approach satisfies the stated goal throughout the Kubernetes platform by showing all entry points. This method is helpful to map out all security controls and standards to understand their coverage better.

Scenario Approach

The scenario approach helps identify attack vectors that are open to threat actors under certain circumstances. In this case, the scenario-based method leverages much of the detail in the bottom-up approach but in a highly realistic manner. This approach also provides more focus on more prevalent attack vectors.

Here’s a summary of the attack trees that are open-sourced and available on GitHub:

Bottom-Up Approach: Malicious Code Execution

The main goal here is to execute malicious code on a cluster. However, to gain a foothold, you must compromise an application that provides access to the container.

Once a threat actor can access the container, they will load more malicious code into the environment. If they can obtain the image pull secret, the threat actor may poison the repository to initiate a wider distribution of malicious code.

Bottom-Up Approach: Establish Persistence

The primary objective of this attack tree is to discover the different ways a hacker might try to gain access to the cluster. This method also investigates different periods of longevity.

In this case, one branch will focus on reading secrets held within the cluster. This approach helps attackers exploit other vulnerable areas. The second branch focuses on threats after an attacker gains access to a container. They will leverage misconfigurations and attempt to establish persistence resilient to containers, nodes, or pod restarts.

Bottom-Up Approach: Access Sensitive Data

Most leading approaches concentrate on exploiting misconfigured RBAC permissions to read secret data directly from the cluster. Some other methods include viewing all the data stored within logs. It’s almost like eavesdropping on network traffic and communications.

Bottom-Up Approach: Denial Of Service

This attack tree investigates different approaches an attacker can take to initiate a DoS attack on the cluster. The first method follows a compromised container scenario where an attacker attempts to DoS the cluster from within. The aim here is to exhaust all its resources.

The second method concentrates on a threat actor who has network access to the cluster control pane. In this scenario, they might try to flood the network at the most suitable endpoints. Again, the goal here is to exhaust all resources.

Scenario: Compromised Applications Leads to Foothold in Container

This scenario focuses on potential vectors that are probably open to an attacker after exploiting an application running within a container. This can lead to remote code execution within the container through programmatic or shell access mechanisms.

Scenario: Attacker on the Network

This scenario concentrates on insider threats. An internal attacker with network access to the Kubernetes cluster will probably have many user privileges without direct access to the cluster. However, you can quickly mitigate most of these threats with appropriate Kubernetes configurations and firewalls.

You can find out more from the Kubernetes Security Audit Working Group and their findings in performing a security audit and producing artifacts as a threat model and whitepaper. They focus on different parts of the Kubernetes cluster, and it’s worth the time and effort to read through it.

Other Kubernetes best practices and recommendations include the following:

  • Always run pods and containers following the least privileges policy (whenever possible).
  • Demand strong authentication and authorization protocols to limit administrator and user access (and limit the attack surface).
  • Encrypt data to ensure confidentiality.
  • Leverage firewalls to limit unnecessary connectivity.
  • Limit potential damage by using network separation controls.
  • Monitor activity via log auditing.
  • Regularly review all settings and use vulnerability scans to identify potential risks and apply security patches.
  • Scan pods and containers for misconfigurations and vulnerabilities.

Secure your K8s Environment with Policy As Code

The exuberant number of best practices, configurations, and maintainability necessary to prevent hackers from exploiting an attack vector makes managing Kubernetes a challenging task for even seasoned experts. Magalix provides one of the largest scalable Policy-as-Code libraries to simplify and reduce the complexity of managing secure K8s.

Policies include:

  • Containers should not be running as root.
  • Containers are missing securityContext.
  • RBAC Protect cluster-admin ClusterRoleBindings.
  • Prohibit RBAC Wildcards for Verbs.
  • Services should not be using NodePort.
  • Containers are missing Liveness Probe.
  • Containers should mount the root filesystem as read-only.
  • Containers should not share hostIPC.
  • Containers should not be using hostPort.
  • Containers should not be mounting the Docker sockets.

With Magalix, you can also programmatically enforce security and compliance standards with policy-as-code. This approach helps provide developer-centric experiences that complement continuous deployment protocols for cloud-native applications. In this scenario, automated operators within the cluster will continuously monitor the repositories for changes.

When using policy-as-code, you can also develop a centralized playbook enacted and enforced across the whole software development lifecycle. This approach helps accelerate innovation without compromising on security.

When you build cloud-native applications following the recommendations listed above, development teams essentially weave security into the fabric of the whole application. As such, it’ll provide the foundation to scale securely while delivering enhanced user experiences.

To learn more about Kubernetes security and how you can take advantage of policy-as-code, request a consultation.