CVE-2022-24817: Github.com/fluxcd/flux2 Improper Kubeconfig Validation Allows Arbitrary Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vvmq-fwmg-2gjc",
  "modified" : "2022-05-26T20:07:54Z",
  "published" : "2022-05-16T18:13:51Z",
  "aliases" : [ "CVE-2022-24817" ],
  "summary" : "Improper kubeconfig validation allows arbitrary code execution",
  "details" : "Flux2 can reconcile the state of a remote cluster when provided with a [kubeconfig](https://kubernetes.io/docs/concepts/configuration/organize-cluster-access-kubeconfig/#file-references) with the correct access rights. `Kubeconfig` files can define [commands](https://kubernetes.io/docs/reference/access-authn-authz/authentication/#client-go-credential-plugins) to be executed to generate on-demand authentication tokens. A malicious user with write access to a Flux source or direct access to the target cluster, could craft a `kubeconfig` to execute arbitrary code inside the controller’s container.\n\nIn multi-tenancy deployments this can also lead to privilege escalation if the controller's service account has elevated permissions.\n\n### Impact\n\nWithin the affected versions range, one of the permissions set below would be required for the vulnerability to be exploited:\n- Direct access to the cluster to create Flux `Kustomization` or `HelmRelease` objects and Kubernetes Secrets.\n- Direct access to the cluster to modify existing Kubernetes secrets being used as `kubeconfig` in existing Flux `Kustomization` or `HelmRelease` objects.\n- Direct access to the cluster to modify existing Flux `Kustomization` or `HelmRelease` objects and access to create or modify existing Kubernetes secrets.\n- Access rights to make changes to a configured Flux Source (i.e. Git repository).\n\n### Patches\n\nThis vulnerability was fixed in kustomize-controller [v0.23.0](https://github.com/fluxcd/kustomize-controller/releases/tag/v0.23.0) and helm-controller [v0.19.0](https://github.com/fluxcd/helm-controller/releases/tag/v0.19.0), both included in flux2 [v0.29.0](https://github.com/fluxcd/flux2/releases/tag/v0.29.0). Starting from the fixed versions, both controllers disable the use of command execution from `kubeconfig` files by default, users have to opt-in by adding the flag `--insecure-kubeconfig-exec` to the controller’s command arguments. Users are no longer allowed to refer to files in the controller’s filesystem in the `kubeconfig` files provided for the remote apply feature.\n\n### Workarounds\n\n- The functionality can be disabled via Validating Admission webhooks (e.g. OPA Gatekeeper, Kyverno) by restricting users from being able to set the `spec.kubeConfig` field in Flux `Kustomization` and `HelmRelease` objects.\n- Applying restrictive AppArmor and SELinux profiles on the controller’s pod to limit what binaries can be executed.\n\n### Credits\n\nThe Flux engineering team found and patched this vulnerability.\n\n### For more information\n\nIf you have any questions or comments about this advisory please open an issue in the [flux2 repository](http://github.com/fluxcd/flux2).\n",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/fluxcd/flux2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.1.0"
      }, {
        "fixed" : "0.29.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/fluxcd/kustomize-controller"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.1.0"
      }, {
        "fixed" : "0.23.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/fluxcd/helm-controller"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.2.0"
      }, {
        "fixed" : "0.19.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fluxcd/flux2/security/advisories/GHSA-vvmq-fwmg-2gjc"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2022-24817"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fluxcd/flux2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-94" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-05-16T18:13:51Z",
    "nvd_published_at" : "2022-05-06T00:15:00Z"
  }
}