Attacking and Defending Kubernetes - Nithin Jois

Attacking and Defending Kubernetes
A Brief Overview
Copyright - we45, 2020

Nithin Jois
● Senior Security Solutions Engineer at we45
● DevOps, Security Engineering and DevSecOps for clients
● Co-lead developer - ThreatPlaybook
● Core-developer - Orchestron
● Speaker/Trainer at multiple security and industry events
Twitter : @bondijois
LinkedIn : https://www.linkedin.com/in/bondijois/
E-mail : nithin.jois@we45.com

Virtualization
Traditional architecture Virtual architecture

Containers To The Rescue!

Containers What??..
● OS level virtualization for running
multiple isolated* systems using
host resources
● Abstraction layer that packages
code and dependencies together

Container Orchestration

List of Container Orchestrators

Image Registry
Node 4
Node 3
Node 2
Node 1
API
CLI
UI
User

Interface
Command Line

Interface
Kubernetes Master
API
Server
Scheduler Controller
etcd
Kubernetes Architecture

Kubernetes Terms
• Cluster = > A Collection of Worker Nodes (that run workloads) and a Kubernetes
Master (that controls the workers)
• Node => A Worker Machine
• Pod => Smallest K8s Object. Represents set of running containers in the cluster
• Deployment => Object that manages a replicated application.
• Service => An Object that how applications are accessed. Typically described Ports
and LoadBalancers

Demo: Setting up a K8s cluster

An Attacker’s View of K8s

The Kubernetes Threat Model
K8s Threat Model
User compromises
the cluster
Users can access Cluster/Controller without authentication
Users can access the Cluster with stolen secrets/ tokens to perform sensitive operations on Cluster
User can tamper with user cert settings and gain access to Cluster as a genuine user
User has unrestricted access across the Cluster
User has highly privileged access across the Cluster
Malicious App (Container)
Compromises the Cluster
Attacker is able to RCE into a container and subsequently gain access
to other services, pods etc on the Cluster to steal sensitive information
Org runs backdoored/Compromised container in the Cluster, that is
able to access other resources on/ across the cluster and steal sensitive information
Attacker is able to perform CPU/mem intensive Ops across the cluster
and bring it down
Attacker gets a trojanized image to run on the cluster and
compromise sensitive information
Backdoored/ compromised container accesses shared resources
and runs ransomware / affects availability to shared resources
Compromise secrets
Gain access to DB/ FS/ Sensitive Information
Gain access to other namespaces for
Cross-Cluster compromise
Access Kube API and Controller to access
K8s Management Sensitive Info
Compromise secrets
Gain access to DB/ FS/ Sensitive Information
Gain access to other namespaces for
Cross-Cluster compromise
Access Kube API and Controller to access
K8s Management Sensitive Info
Malicious node
compromises
the cluster
Malicious node registers itself as a genuine node to the cluster and compromises the node therefrom
Exploit against Node escalates privileges to Kube deployment and compromises cluster

K8s Services - Cluster
Port Process Description
4149/TCP kubelet Default Port for Container Metrics
10250/TCP kubelet API that allows full node access
10255/TCP kubelet
Unauthenticated Read-only port with
access to node state
10256/TCP kube-proxy Health check server for Kube Proxy
9099/TCP calico-felix Healthcheck for Calico-Canal (SDN)
6443/TCP kube-apiserver K8s API Port

Observations
Application Layer
Container Layer
K8s Cluster Layer

Application Layer
• Vulnerable Application - Insecure Deserialization
• Insecure Secrets Management - No Protection of
Encryption Key
• Redis - No Authentication

Container Layer
• Running as “root"
• No Hardening of Container Runtime
• Insecure Secrets in Container Environment
Variables

K8s Cluster Layer
• No Network Policy
• Especially Egress Controls
• No Authentication or Access Control
• No Logical Segmentation - Namespaces
• No Pod Security Controls
• Lack of Monitoring

Securing K8s (Container
Orchestration)

K8s Security Model
• Restrict access to kubectl
• Use RBAC
• Use a network policy
• Use namespaces
• Bootstrap TLS
Set up a cluster
Follow security hygiene
• Keep Kubernetes updated
• Use a minimal OS
• Use minimal IAM roles
• Use private IPs on your nodes
• Monitor access with audit logging
• Verify binaries that are deployed
• Disable dashboard
• Disable default service
account token
• Protect node metadata
• Scan images for known
vulnerabilities
Prevent known attacks
• Set a pod security policy
• Protect secrets
• Consider sandboxing
• Limit the identity used by pods
• Use a service mesh for
authentication/ encryption
Prevent/limit impact of
microservice compromise

K8s Authentication and Access Control
•Authentication
•Access Control
•Admission Controller

K8s Authentication - Users
• Kubernetes has two types of users:
• Service Accounts => Managed by Kubernetes
• Managed by the K8s API, bound to specific namespaces
• Normal Users => Managed by an outside service
• The user typing kubectl must authenticate or be an anonymous user

K8s Authentication Methods
•Authentication Strategies:
•Client Certificates (X.509)
•HTTP Basic Authentication
•Bearer Tokens
•Authentication Proxies or Webhook
•LDAP, SAML, Kerberos
•You can use multiple authentication methods at once

Client Certificates
• Certificate Signing request for user “abhay” who is part of two groups, “app1” and
“app2”
• You can also use comprehensive secrets management system like Hashicorp Vault to
be the CA
openssl req -new -key abhay.pem -out abhay-csr.pem
-subj “/CN=abhay/O=app1/O=app2"

Static Token File
• Inject Bearer Tokens into the Kubernetes cluster with the
• -- token-auth-file=SOMEFILE CLI arg
• Token Files CANNOT be changed without restarting the API Server
• Tokens are FOREVER. They last indefinitely
token,user,uid,"group1,group2,group3"
Authorization: Bearer 31ada4fd-adec-460c-809a-9e56ceb75269

HTTP Basic Auth - Static Password Files
• Similar to tokens
• Inject Static password files into K8s cluster with the flag
• --basic-auth-file=SOMEFILE
• Password CANNOT be changed without starting the API Server
minikube mount $PWD:/var/lib/localkube/certs/pass
minikube start --extra-config=apiserver.basic-auth-
file=/var/lib/localkube/certs/pass/mypass
Authorization: Basic Base64Encoded(username:password)

Authentication Proxies/Webhooks
• Authentication using Proxies/Webhooks
• OpenID Connect Tokens (OAuth2 Flavor) - Azure Active Directory, Salesforce,
Google
• Access Token returned with ID Token (JWT)
X-Remote-User: fido
X-Remote-Group: dogs
X-Remote-Group: dachshunds
X-Remote-Extra-Acme.com%2Fproject: some-project
X-Remote-Extra-Scopes: openid
X-Remote-Extra-Scopes: profile

Service Accounts
• You can create service accounts for services (CI, Apps, etc) to access the cluster to perform operations
• Example: Jenkins builds a new docker image and deploys the image to the cluster on the staging
namespace
• Service accounts typically use JWTs signed with the API’s TLS Server OR a PEM file provided by the
user
kubectl create serviceaccount jenkins
serviceaccount "jenkins" created
$ kubectl get serviceaccounts jenkins -o yaml
apiVersion: v1
kind: ServiceAccount
metadata:
# ...
secrets:
- name: jenkins-token-1yvwg

Service Account Secrets
• Service Accounts for the namespace are injected into the Pod at the
• /run/secrets/kubernetes.io/serviceaccount path
kubectl get secret jenkins-token-1yvwg -o yaml
apiVersion: v1
data:
ca.crt: (APISERVER'S CA BASE64 ENCODED)
namespace: ZGVmYXVsdA==
token: (BEARER TOKEN BASE64 ENCODED)
kind: Secret
metadata:
# ...
type: kubernetes.io/service-account-token

Authorization - K8s
• K8s has a clear separation between Authentication (various strategies) and
Authorization
• Types of Authorization:
• Node
• RBAC => Role Based Access Control
• ABAC => Attribute Based Access Control
• Webhooks

RBAC K8s Authorization
• RBAC Authorization refers to Roles that contain
rules of Permissions
• Permissions are only additive (No Deny)
• Easy to manage, when you have a a clearly defined
set of privileges for the roles
• Two Types:
• ClusterRole => Role that applies across the
Cluster (across Namespaces)
• Role => applies to Permissions that work
across a single namespace
kind: Role
apiVersion:
rbac.authorization.k8s.io/
v1
metadata:
namespace: default
name: pod-reader
rules:
- apiGroups: [""] # ""
indicates the core API
group
resources: ["pods"]
verbs: ["get", "watch",
"list"]

Demo: Role Based Access Control

ABAC Authorization
• ABAC == “Attribute Based Authentication System”
• Simple mapping (JSON) of user access to specific resources based on their attributes
• Load the ABAC Policy with a --authorization-policy-file=SomeFile, format of one object
per line
{"apiVersion":
"abac.authorization.kubernet
es.io/v1beta1", "kind":
"Policy", "spec": {"user":
"alice", "namespace": "*",
"resource": "*", "apiGroup":
"*"}}
user ‘alice’ has access to all
namespaces/resources in the
cluster
{"apiVersion":
"abac.authorization.kubernetes
.io/v1beta1", "kind":
"Policy", "spec": {"user":
"bob", "namespace": "owasp",
"resource": "pods",
"readonly": true}}
user ‘bob’ can only read pods in
the ‘owasp’ namespace

Admission Controllers
• Admission Controller is an additional Access Control Layer for the Kubernetes API
• Think of it like a Validation Filter that validates admission/rejection based on certain
rules/features enabled
• Admission Controllers work AFTER the user/account is authenticated and
authorized
• They are enabled based on the Cluster Administrator’s configuration of the same
kube-apiserver --enable-admission-
plugins=NamespaceLifecyle,LimitRanger ...

Useful Admission Controller Plugins
• AlwaysPullImages => forces the pod image pull policy to always. Ensures that
private images are authenticated when there’s a pull.
• DenyEscalatingExec => Deny ‘exec’ or ‘attach’ operations to Pods that run
with elevated privileges (host access). Pods => Privileges, Host IPC Namespace, Host
PID Namespace
• EventRateLimit => Rate Limit for K8s API. Prevents DoS
• LimitRanger => Enforce the LimitRange directive to protect against excessive
consumption by Pod

Useful Admission Controller Plugins - 2
• PodSecurityPolicy => Multiple Configuration Parameters (including Seccomp,
AppArmor), etc to protect Pod against attacks (rule based)
• NamespaceLifecycle => Prevents against loading resources in “to-be-deleted”
namespaces. Also prevents against resources being allocated in default, kube-system
and kube-public namespaces
• NodeRestriction => Node Authorization Privileges for the kubelet
• ResourceQuota => Enforces Consumable Resources by a Pod

Other Access Control Good Practices
• Secure/Disable Dashboard
• Never run LoadBalancer on Dashboard Service
• Leverage RBAC
• Create and Enforce controls on Namespaces
• Logical Segmentation (however weak)
• Better way to think about Access Control

Pod Security Policy
•Ruleset that defines specific rules for a
Pod to run in a K8s cluster
•Optional, but highly recommended
•Admission Controller - Disallows
containers from being loaded on the
Pod, if it violates the rules

Pod Security Policy - Parameters
• Privileged/UnPrivileged
• Host Namespaces
• Host Networking and Ports
• Volumes
• Paths
• User and Group IDs for the
Containers
• Linux Capabilities
• SELinux
• AppArmor/Seccomp
• ReadOnly RootFS
• Allow/Disallow PrivilegeEscalation

apiVersion: policy/v1beta1
kind: PodSecurityPolicy
metadata:
name: restricted
annotations:
seccomp.security.alpha.kubernetes.io/allowedProfileNames: 'docker/default'
apparmor.security.beta.kubernetes.io/allowedProfileNames: 'runtime/default'
seccomp.security.alpha.kubernetes.io/defaultProfileName: 'docker/default'
apparmor.security.beta.kubernetes.io/defaultProfileName: 'runtime/default'
spec:
privileged: false
# Required to prevent escalations to root.
allowPrivilegeEscalation: false
# This is redundant with non-root + disallow privilege escalation,
# but we can provide it for defense in depth.
requiredDropCapabilities:
- ALL
# Allow core volume types.

volumes:
- 'configMap'
- 'emptyDir'
- 'projected'
- 'secret'
- 'downwardAPI'
# Assume that persistentVolumes set up by the cluster admin are safe to use.
- 'persistentVolumeClaim'
hostNetwork: false
hostIPC: false
hostPID: false
runAsUser:
# Require the container to run without root privileges.
rule: 'MustRunAsNonRoot'
seLinux:
# This policy assumes the nodes are using AppArmor rather than SELinux.
rule: 'RunAsAny'
supplementalGroups:
rule: 'MustRunAs'
ranges:
# Forbid adding the root group.
- min: 1
max: 65535
fsGroup:
rule: 'MustRunAs'
ranges:
# Forbid adding the root group.
- min: 1
max: 65535
readOnlyRootFilesystem: false

Demo: Pod Security Policy

Pod Security Policy - Gotchas
•AppArmor/Seccomp is not a silver-bullet! Attackers can still perform
Network Layer Attacks, if your apps are vulnerable
•Profiling Syscalls for appropriate restrictions - especially of interpreted
languages, is 😥
•Doesn’t protect against Network Layer Attacks

K8s Secrets
• Kubernetes has a secrets object that you can use to store secrets
• Secrets can be injected into the containers as ENVVARs or Mounted FilePaths, or
injected from files
• Access to Secrets can also be restricted with Authorization Systems
# from file
kubectl create secret generic db-user-pass --from-file=./username.txt --from-file=./
password.txt
#from literal
kubectl create secret generic prod-db-secret --from-literal=username=produser --from-
literal=password=Y4nys7f11

Points to Ponder…
• Secrets are NOT encrypted at rest
• Not in Memory
• Not in etcd
• Injected Secrets (into Container) are in plaintext/base64encoded
• K8s has an experimental plugin that encrypts secrets in etcd:
• But, they are still decrypted and injected to the container in plaintext

Secret Input/Output
• Input
• Secrets from Literals
• Secrets from file/data
• Output
• Volume Mount
• Environment Variables

Secrets Gotchas
• Secrets get committed to repos (sometimes, public ones)
• Secrets can get exposed to unauthorized users within the cluster
• Secrets are available unencrypted in etcd and to cluster resources

Secrets Management - K8s

Common Characteristics
• Secrets Management Solutions
• Centralized Storehouse of secrets and encrypted
datasets
• Secrets Management solutions in the cloud -
Plethora of APIs and reousrces to handle this
requirement
• Data is decrypted before being injected into the
cluster
• Data is (usually) stored in etcd with encryption

Kubeseal - Sealed Secrets
• New Third Party Resource from BitNami Engineering
• Idea => Anyone can create a secret, but nobody but the controller can decrypt the
secret
LifeofaSealedSecret
Secret
Sealed Secret
Kubeseal
encrypts secret
Safe to post publicly
Secret
Sealed Secret
Kubernetes cluster
Decrypted by
Controller

Sealed Secrets - Process
Encryption Process
Decryption Process

Demo: Kubeseal - Shared Secrets

Dynamic Secrets
• Generated on-demand and unique to each client/pod
• Destroys secret/credential when lease expires
Vault
Request DB credential
Return dynamic credential
Valid for 7 days
Create user…
With password…

Auditing K8s

Auditing kube-apiserver
• Helps Cluster Admins and Security teams to answer the following:
•What happened?
•When?
•Who initiated it?
•What did it happen on?
•Where was it observed?
•Where was it initiated?
•Where was it going?

Audit policy Example
# Log all requests at RequestResponse level

apiVersion: audit.k8s.io/v1

kind: Policy

rules:

- level: RequestResponse

{
"kind":"Event",
"apiVersion":"audit.k8s.io/v1beta1",
"metadata":{ "creationTimestamp":"2019-03-21T14:30:12Z" },
"level":"Metadata",
“timestamp":"2019-03-21T14:30:12Z",
"auditID":"442d9cc4-bfc5-4a59-b688-dcebe905ce55",
"stage":"RequestReceived",
"requestURI":"/api/v1/namespaces/default/services",
"verb":"list",
"user": {
"username":"example@example.org",
"groups":[ "system:authenticated" ]
},
"sourceIPs":[ "192.168.1.139" ],
"objectRef": {
"resource":"services",
"namespace":"default",
"apiVersion":"v1"
},
"requestReceivedTimestamp":"2019-03-21T14:30:12.720183Z",
"stageTimestamp":"2019-03-21T14:30:12.720183Z"
Audit Log Example

Auditing Cluster Security Controls
• Pods running as ‘root’
• Privileged==true
• Scary capabilities
• Exposed FileSystem
• System resource consumption
• Egress Traffic
• and more…..

Demo: KubeAudit

K8s Vulnerability Assessment

Potential Vulnerabilities in K8s
● Insecure Deployment Configurations
● Insecure Containers/Pods
● Insecure Applications & Libraries
● Insecure third-party services

Potential flaws in K8s YAML Spec
● Storage of Sensitive Info in YAML resources
● Using unencrypted ENV vars and secrets
● Insecure Network, Volume/mountPath configurations
● Lack of resource limits in place
● Privileged access to pods
● Extensive Kernel Capabilities

K8s CIS-Benchmark Checks
● Setup Authentication and Authorization
● Secure Data in Transit
● Secure Data at Rest
● Employ Least Privileges
● Additional Runtime Controls

CIS Best-Practices - kube-bench
● Checks if K8s deployment is secure by
running checks documented in CIS-K8s-
Benchmark.
● Checks can be performed on both Master
and Node machines
● Checks performed are stored as YAML specs,
making it easy to modify
● Results are given in Pass, Fail and Info format

Scanning K8s Cluster - kube-hunter
● Scans for security issues on K8s clusters
● Has three scanning options
○ Remote Scanning: kube-hunter.py --remote some.node.com
○ Internal Scanning : kube-hunter.py --internal
○ Network Scanning: kube-hunter.py --cidr 192.168.0.0/24
● For a more ‘Attack’ like scan, ‘--active’ flag can be used.
○ Exploits vulnerabilities found to explore further
○ kube-hunter.py --remote some.domain.com --active
■ Can change state of the cluster, which could be harmful

Demo: Kube-Hunter

Kubernetes CI/CD

K8s Security Pipeline
● Application Security Scans
● SAST
● SCA
● Docker Security Scans
● Clair
● Anchore
● Kubernetes Security Scans
● KubeSec
● KubeHunter
● Deploy Securely to K8s

Demo: K8s Security Pipeline
Bandit SAST Safety SCA Docker Build Clair Scan KubeSec
Deploy to K8s
cluster

Thank You!
@bondijois
https://linkedin.com/in/bondijois

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