GHSA-6PRH-2H8M-C8CW

Vulnerability from github – Published: 2026-10-20 18:26 – Updated: 2026-10-20 18:26
VLAI
Summary
MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies
Details

Summary

In affected versions, the SDK's HTTP client transports and OAuth requests followed redirects to any origin.

If an MCP server or authorization server redirected a request to another origin, that origin received custom request headers (such as an X-API-Key set in requestInit.headers) and the mcp-session-id header. On a 307 or 308 it also received the request body, including OAuth token requests with their refresh_token and client_secret.

On current runtimes fetch already drops the Authorization header across origins.

Am I affected?

Yes, if your application uses StreamableHTTPClientTransport, SSEClientTransport, or the SDK's OAuth client functions such as auth(). stdio clients are not affected.

Affected versions:

  • @modelcontextprotocol/sdk all versions through 1.31.0
  • @modelcontextprotocol/client 2.0.0 through 2.2.0

Fix

Upgrade to:

  • 1.x: @modelcontextprotocol/sdk 1.32.0 or later
  • 2.x: @modelcontextprotocol/client 2.3.0 or later

Redirects are now followed only within the same origin, and not at all in browsers. If your MCP server or authorization server redirects to another origin on purpose, configure the final URL instead. Setting redirectPolicy: 'follow' on a transport restores the old behaviour and the exposure.

If a redirect may have reached a host you do not control, rotate the API keys and client_secret your application held and revoke its tokens.

If you cannot upgrade yet, pass a fetch that refuses redirects, for example (url, init) => fetch(url, { ...init, redirect: 'error' }).

Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@modelcontextprotocol/sdk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.32.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "@modelcontextprotocol/client"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-111769"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-200"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-20T18:26:30Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\nIn affected versions, the SDK\u0027s HTTP client transports and OAuth requests followed redirects to any origin.\n\nIf an MCP server or authorization server redirected a request to another origin, that origin received custom request headers (such as an `X-API-Key` set in `requestInit.headers`) and the `mcp-session-id` header. On a `307` or `308` it also received the request body, including OAuth token requests with their `refresh_token` and `client_secret`.\n\nOn current runtimes `fetch` already drops the `Authorization` header across origins.\n\n### Am I affected?\nYes, if your application uses `StreamableHTTPClientTransport`, `SSEClientTransport`, or the SDK\u0027s OAuth client functions such as `auth()`. stdio clients are not affected.\n\nAffected versions:\n\n- `@modelcontextprotocol/sdk` all versions through 1.31.0\n- `@modelcontextprotocol/client` 2.0.0 through 2.2.0\n\n### Fix\nUpgrade to:\n\n- 1.x: `@modelcontextprotocol/sdk` 1.32.0 or later\n- 2.x: `@modelcontextprotocol/client` 2.3.0 or later\n\nRedirects are now followed only within the same origin, and not at all in browsers. If your MCP server or authorization server redirects to another origin on purpose, configure the final URL instead. Setting `redirectPolicy: \u0027follow\u0027` on a transport restores the old behaviour and the exposure.\n\nIf a redirect may have reached a host you do not control, rotate the API keys and `client_secret` your application held and revoke its tokens.\n\nIf you cannot upgrade yet, pass a `fetch` that refuses redirects, for example `(url, init) =\u003e fetch(url, { ...init, redirect: \u0027error\u0027 })`.",
  "id": "GHSA-6prh-2h8m-c8cw",
  "modified": "2026-10-20T18:26:31Z",
  "published": "2026-10-20T18:26:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-6prh-2h8m-c8cw"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/pull/2901"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/pull/2902"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/commit/30bfe5139f4b0825c90cd725f9a7e3f9af5e120d"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/commit/433eb413dc305ebeb93b8ebcde0095a8fc0d5fa0"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies"
}



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