Risks of adding privileged processes in pods

By default, Kubernetes allows the addition of Linux capabilities to containers, which can pose significant security risks if not properly managed.

Potential Security Threats

Unauthorized Port Access:

CAP_NET_BIND_SERVICE capability allows containers to bind to privileged ports (ports below 1024). If an attacker gains this capability, they could open ports within the cluster, potentially exposing the cluster to external access and attacks.

Escalation of Privileges:

Containers running with elevated privileges can exploit vulnerabilities to gain higher-level access within the cluster. This can lead to unauthorized data access, service disruptions, or control over other containers.

Network Manipulation:

With capabilities like CAP_NET_RAW, containers can manipulate network traffic, potentially leading to man-in-the-middle attacks, traffic interception, or unauthorized network scanning within the cluster.

Mitigation Measures

To mitigate these risks, it is essential to restrict Linux capabilities in containers. This can be achieved through the use of Pod Security Policies (PSPs) or Pod Security Standards (PSS) in newer Kubernetes versions:

Drop All Capabilities:

By default, drop all Linux capabilities from containers to prevent any unwanted privileges. This can be enforced using the requiredDropCapabilities setting in the Pod Security Policy:

apiVersion: policy/v1beta1

kind: PodSecurityPolicy

metadata:

  name: restricted-psp

spec:

  requiredDropCapabilities:

    - ALL

  # Other necessary security settings

Add Only Required Capabilities:

Only allow the addition of specific, necessary capabilities for containers. This principle of least privilege ensures that containers operate with only the permissions they need to function correctly.

apiVersion: policy/v1beta1

kind: PodSecurityPolicy

metadata:

  name: specific-psp

spec:

  allowedCapabilities:

    - CAP_NET_BIND_SERVICE  # Only if absolutely necessary

  requiredDropCapabilities:

    - ALL

  # Other necessary security settings

Use Pod Security Standards (PSS):

With the deprecation of PSPs in Kubernetes, it is recommended to adopt Pod Security Standards (PSS) to enforce security best practices at the namespace level. PSS defines three policies: Privileged, Baseline, and Restricted. The Restricted policy ensures the least privilege configuration, including the dropping of all capabilities unless explicitly allowed.

Regular Audits and Monitoring:

Conduct regular audits of your cluster's security configurations and monitor for any deviations from the established security policies. Use Kubernetes-native tools and third-party solutions for continuous security monitoring and compliance checks.