Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource server

{
  "id": "bef26a42b800ca57b47e80bed15e2f04a7d8ba307fe1e1b3ec2fa75f01fc91cf",
  "url": "https://www.cve.org/CVERecord?id=CVE-2026-116684",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource server",
    "summary": "The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.10.0 until 1.30.0 and 2.2.0, server-side bearer authentication configured through AuthSettings with token_verifier accepts a valid token issued for another service when the authorization server serves multiple resources and the TokenVerifier does not independently validate the aud audience. This resource-confusion flaw lets a token holder authenticate to the wrong MCP server and exercise that token's resulting access. This issue is fixed in versions 1.30.0 and 2.2.0.",
    "evidence": "cve:CVE-2026-116684",
    "products": [
      {
        "name": {
          "value": "python-sdk",
          "evidence": "/containers/cna/affected/0/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-116684",
      "aliases": [
        "CVE-2026-116684"
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "scope": "UNCHANGED",
            "version": "3.1",
            "baseScore": 6.8,
            "attackVector": "NETWORK",
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N",
            "integrityImpact": "HIGH",
            "userInteraction": "NONE",
            "attackComplexity": "HIGH",
            "availabilityImpact": "NONE",
            "privilegesRequired": "LOW",
            "confidentialityImpact": "HIGH"
          }
        }
      ],
      "affected": [
        {
          "vendor": "modelcontextprotocol",
          "product": "python-sdk",
          "versions": [
            {
              "status": "affected",
              "version": ">= 1.10.0, < 1.30.0"
            },
            {
              "status": "affected",
              "version": ">= 2.0.0, < 2.2.0"
            }
          ]
        }
      ],
      "modified": "2026-10-27T19:12:24.255Z",
      "provider": "cve",
      "references": [
        "https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-w4fh-qvv9-3v23",
        "https://github.com/modelcontextprotocol/python-sdk/pull/3447",
        "https://github.com/modelcontextprotocol/python-sdk/pull/3451",
        "https://github.com/modelcontextprotocol/python-sdk/commit/0c9136841ff092987a20700ff9c2c9789bda2f40",
        "https://github.com/modelcontextprotocol/python-sdk/commit/8c2fa6eabacde869d75568e33b9d466b58c2f512",
        "https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0",
        "https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0"
      ],
      "provider_metadata": {
        "cna": {
          "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
          "shortName": "GitHub_M",
          "dateUpdated": "2026-10-27T19:12:24.255Z"
        }
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-116684",
        "evidence": "/cveMetadata/cveId"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/containers/cna/metrics"
  },
  "source_id": "core-cve",
  "document_id": 398111,
  "published_at": "2026-10-27T19:12:24.255+00:00"
}