10_threat_model_k8s_telecom

Part 10: Threat Model - Kubernetes + Telecom

Learning Objective: Apply STRIDE threat modeling to Kubernetes-based telecom deployments.

K8s + Telecom Attack Surface

graph TB
    subgraph "K8s Control Plane"
        API[API Server]
        etcd[(etcd)]
        Scheduler[Scheduler]
    end
    
    subgraph "Worker Nodes"
        subgraph "Namespace: open5gs"
            AMF_Pod[AMF Pod]
            SMF_Pod[SMF Pod]
            UPF_Pod[UPF Pod]
        end
        
        subgraph "Namespace: ueransim"
            gNB_Pod[gNB Pod]
        end
    end
    
    Attacker[🔴 Attacker]
    
    Attacker -.->|❌ 1. Exploit
unauth API| API
    Attacker -.->|❌ 2. Container
escape| AMF_Pod
    Attacker -.->|❌ 3. etcd
access| etcd
    Attacker -.->|❌ 4. Network
policy bypass| UPF_Pod
    Attacker -.->|❌ 5. Malicious
Helm chart| SMF_Pod
    
    style Attacker fill:#ff9999
    style API fill:#ffcccc
    style etcd fill:#ffcccc
    style AMF_Pod fill:#ffcccc

Threat Catalog

1. Container Escape from NF Pods (E)

Attack Vector:

Exploit kernel vulnerability (e.g., dirty pipe, runc)
Escape from AMF/SMF/UPF container to host

Impact:

Elevation of Privilege: Root access on worker node
Access to all pods on the node

Mitigation:

✅ Use read-only root filesystem
✅ Run as non-root user (UID > 1000)
✅ Enable seccomp profiles (restrict syscalls)
✅ Use AppArmor/SELinux
✅ Keep kernel updated

Example Pod Security:

securityContext:
  runAsNonRoot: true
  runAsUser: 1000
  readOnlyRootFilesystem: true
  allowPrivilegeEscalation: false
  capabilities:
    drop:
      - ALL

STRIDE Score: E=Critical

2. K8s RBAC Misconfiguration (E, I)

Attack Vector:

Overly permissive RBAC roles
Service account with cluster-admin privileges

Impact:

Elevation of Privilege: Attacker gains cluster-admin
Information Disclosure: Read all secrets (subscriber data, TLS certs)

Mitigation:

✅ Principle of least privilege (minimal RBAC)
✅ Separate service accounts per NF
✅ Audit RBAC with kubectl auth can-i --list

Example Minimal RBAC:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: amf-role
  namespace: open5gs
rules:
  - apiGroups: [""]
    resources: ["configmaps"]
    verbs: ["get", "list"]

STRIDE Score: E=High, I=High

3. NetworkPolicy Bypass (I, T)

Attack Vector:

Missing NetworkPolicy allows cross-namespace traffic
UE pod in ueransim namespace accesses AMF pod in open5gs namespace

Impact:

Information Disclosure: Intercept SBI traffic
Tampering: Modify NF-to-NF communication

Mitigation:

✅ Default-deny NetworkPolicy
✅ Explicit allow rules for N2, N3, SBI

Example NetworkPolicy:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: amf-ingress
  namespace: open5gs
spec:
  podSelector:
    matchLabels:
      app: amf
  policyTypes:
    - Ingress
  ingress:
    - from:
        - namespaceSelector:
            matchLabels:
              name: ueransim
      ports:
        - protocol: SCTP
          port: 38412  # N2 NGAP — uses SCTP per 3GPP TS 38.412, not TCP

STRIDE Score: I=High, T=Medium

4. Supply Chain: Malicious Helm Chart (T, E)

Attack Vector:

Use untrusted Helm chart repository
Chart contains backdoored container image

Impact:

Tampering: Malicious code in NF pods
Elevation of Privilege: Backdoor with cluster access

Mitigation:

✅ Use trusted Helm repos (Gradiant, official Open5GS)
✅ Verify chart signatures (helm verify)
✅ Scan images with Trivy/Grype
✅ Use admission controllers (OPA Gatekeeper) to block unsigned images

Example OPA Policy:

package kubernetes.admission

deny[msg] {
  input.request.kind.kind == "Pod"
  image := input.request.object.spec.containers[_].image
  not startswith(image, "open5gs/")
  msg := sprintf("Untrusted image: %v", [image])
}

STRIDE Score: T=Critical, E=Critical

5. etcd Exposure Leaking Subscriber Data (I)

Attack Vector:

etcd exposed without authentication
Attacker reads all K8s secrets (MongoDB credentials, subscriber data)

Impact:

Information Disclosure: All secrets, ConfigMaps, subscriber profiles

Mitigation:

✅ Enable etcd authentication and TLS
✅ Encrypt secrets at rest (EncryptionConfiguration)
✅ Network isolation (etcd only accessible from control plane)

Example Encryption Config:

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - aescbc:
          keys:
            - name: key1
              secret: <base64-encoded-32-byte-key>
      - identity: {}

STRIDE Score: I=Critical

6. Service Mesh for NF-to-NF mTLS (S, T, I)

Attack Vector:

No service mesh → SBI traffic in plaintext
Attacker intercepts AMF ↔ SMF communication

Impact:

Spoofing: Rogue NF impersonates SMF
Tampering: Modify SBI messages
Information Disclosure: Read subscriber data

Mitigation:

✅ Deploy Istio/Linkerd service mesh
✅ Enforce mTLS for all SBI traffic
✅ Use SPIFFE/SPIRE for NF identity

Example Istio PeerAuthentication:

apiVersion: security.istio.io/v1beta1
kind: PeerAuthentication
metadata:
  name: default
  namespace: open5gs
spec:
  mtls:
    mode: STRICT

STRIDE Score: S=High, T=High, I=High

7. Pod Security Standards (E)

Attack Vector:

Privileged pod with hostNetwork: true
Attacker gains access to host network stack

Impact:

Elevation of Privilege: Access to all node traffic

Mitigation:

✅ Enforce Pod Security Standards (PSS)
✅ Use Restricted profile for all NF pods
✅ Disable hostNetwork, hostPID, hostIPC

Example PSS Enforcement:

apiVersion: v1
kind: Namespace
metadata:
  name: open5gs
  labels:
    pod-security.kubernetes.io/enforce: restricted
    pod-security.kubernetes.io/audit: restricted
    pod-security.kubernetes.io/warn: restricted

STRIDE Score: E=High

8. Secrets Management (I)

Attack Vector:

Secrets stored in plaintext ConfigMaps
Attacker reads MongoDB password, TLS private keys

Impact:

Information Disclosure: Database credentials, certificates

Mitigation:

✅ Use K8s Secrets (not ConfigMaps)
✅ External secrets manager (HashiCorp Vault, AWS Secrets Manager)
✅ Rotate secrets regularly

Example External Secrets Operator:

apiVersion: external-secrets.io/v1beta1
kind: ExternalSecret
metadata:
  name: mongodb-creds
  namespace: open5gs
spec:
  secretStoreRef:
    name: vault-backend
  target:
    name: mongodb-secret
  data:
    - secretKey: password
      remoteRef:
        key: mongodb/password

STRIDE Score: I=Critical

9. Resource Exhaustion (D)

Attack Vector:

No resource limits on UPF pod
UPF consumes all node CPU/memory

Impact:

Denial of Service: Other NF pods evicted

Mitigation:

✅ Set resource requests and limits
✅ Use LimitRanges and ResourceQuotas

Example Resource Limits:

resources:
  requests:
    memory: "512Mi"
    cpu: "500m"
  limits:
    memory: "2Gi"
    cpu: "2000m"

STRIDE Score: D=High

10. Admission Control (T, E)

Attack Vector:

No admission controller
Attacker deploys pod with privileged: true

Impact:

Tampering: Modify cluster state
Elevation of Privilege: Root on node

Mitigation:

✅ Enforce the appropriate Pod Security Standards with the built-in Pod Security Admission controller (stable in Kubernetes v1.25+)
✅ Use OPA Gatekeeper for custom policies
✅ Deny privileged containers

Note

PodSecurityPolicy was removed in Kubernetes v1.25. Older clusters that still depend on it need a planned migration to Pod Security Admission or another admission-policy implementation.

Example Gatekeeper Policy:

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sPSPPrivilegedContainer
metadata:
  name: deny-privileged
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod"]

STRIDE Score: T=High, E=Critical

Threat Summary Table

Threat	S	T	I	D	E	Severity
Container Escape					✅	Critical
RBAC Misconfiguration			✅		✅	High
NetworkPolicy Bypass		✅	✅			High
Malicious Helm Chart		✅			✅	Critical
etcd Exposure			✅			Critical
No Service Mesh	✅	✅	✅			High
Pod Security					✅	High
Secrets Exposure			✅			Critical
Resource Exhaustion				✅		High
No Admission Control		✅			✅	Critical

Defense-in-Depth Checklist

Summary

✅ K8s adds new attack surface (container escape, RBAC, NetworkPolicy)
✅ Telecom workloads require strict isolation (slices = namespaces)
✅ Service mesh is critical for SBI mTLS
✅ Defense-in-depth: combine multiple security layers

Congratulations! You've completed the core Open5GS Telecom Security Lab Guide. Continue to the Real-World Attack Case Studies for deep dives into 20 actual telecom attacks. 🎉

Next: Part 11: Real-World Attacks — Core Signaling (SS7 / Diameter / GTP) →

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