Runtime Container Security

Runtime Container Security

Runtime security extends beyond vulnerability scanning to monitor container behavior. Runtime protection tools detect anomalous activities like unexpected process execution, file system modifications, or network connections. These tools establish behavioral baselines during normal operation then alert on deviations that might indicate compromise.

Admission controllers enforce security policies before containers run in orchestration platforms. Kubernetes admission webhooks can validate container configurations, enforce image signing requirements, and ensure compliance with organizational policies. These preventive controls stop insecure containers from ever running rather than trying to detect problems after deployment.

// Kubernetes admission webhook for container security
package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "net/http"
    
    admissionv1 "k8s.io/api/admission/v1"
    corev1 "k8s.io/api/core/v1"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

type SecurityAdmissionWebhook struct {
    trustedRegistries []string
    requiredLabels    []string
    bannedImages      []string
}

func (w *SecurityAdmissionWebhook) HandleAdmission(ar *admissionv1.AdmissionReview) *admissionv1.AdmissionResponse {
    pod := corev1.Pod{}
    if err := json.Unmarshal(ar.Request.Object.Raw, &pod); err != nil {
        return &admissionv1.AdmissionResponse{
            Result: &metav1.Status{
                Message: err.Error(),
            },
        }
    }
    
    // Validate container images
    for _, container := range pod.Spec.Containers {
        // Check trusted registries
        if !w.isFromTrustedRegistry(container.Image) {
            return w.denyResponse(fmt.Sprintf(
                "Image %s is not from a trusted registry", 
                container.Image,
            ))
        }
        
        // Check banned images
        if w.isBannedImage(container.Image) {
            return w.denyResponse(fmt.Sprintf(
                "Image %s is banned due to security vulnerabilities", 
                container.Image,
            ))
        }
        
        // Validate security context
        if container.SecurityContext == nil ||
           container.SecurityContext.RunAsNonRoot == nil ||
           !*container.SecurityContext.RunAsNonRoot {
            return w.denyResponse(
                "Containers must run as non-root user",
            )
        }
        
        // Check for privileged mode
        if container.SecurityContext.Privileged != nil &&
           *container.SecurityContext.Privileged {
            return w.denyResponse(
                "Privileged containers are not allowed",
            )
        }
    }
    
    // Validate pod security standards
    if pod.Spec.HostNetwork {
        return w.denyResponse("Host network access is not allowed")
    }
    
    if pod.Spec.HostPID {
        return w.denyResponse("Host PID namespace access is not allowed")
    }
    
    // Check required labels
    for _, label := range w.requiredLabels {
        if _, exists := pod.Labels[label]; !exists {
            return w.denyResponse(fmt.Sprintf(
                "Required label %s is missing", 
                label,
            ))
        }
    }
    
    return &admissionv1.AdmissionResponse{
        Allowed: true,
    }
}