GHSA-fcpm-6mxq-m5vv: Capsule tenant owners with "patch namespace" permission can hijack system namespaces label
SummaryA 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.DetailsThe 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:**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:**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 installedAuthenticated tenant user with basic RBAC permissions**Step 1: Environment Setup****Step 2: Label Injection Attack****Step 3: Exploitation via TenantResource****Step 4: Verification of Impact****Automated Testing Script:**
A complete vulnerability verification script is available that tests:Label injection into multiple system namespacesTenantResource exploitationCross-tenant resource access verificationImpact assessment and cleanupImpact**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 tokensModification or replication of critical system configurationsCross-tenant data access in shared clustersPotential 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.
CVSS v3.1: 9