GHSA-89XV-2J6F-QHC8

Vulnerability from github – Published: 2026-03-19 16:42 – Updated: 2026-03-25 20:48
VLAI
Summary
Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk
Details

The Go SDK's Streamable HTTP transport accepted browser-generated cross-site POST requests without validating the Origin header and without requiring Content-Type: application/json. In deployments without Authorization, especially stateless or sessionless configurations, this allows an arbitrary website to send MCP requests to a local server and potentially trigger tool execution.

Impact:

A malicious website may have been able to send cross-site POST requests with Content-Type: text/plain, which due to CORS-safelisted properties would reach the MCP message handling without any CORS preflight barrier.

Fix:

The SDK was modified to perform Content-Type header validation for POST requests and introduced a configurable protection for verifying the origin of the request in commit a433a83. Users are advised to update to v1.4.1 to use this additional protection.

Note: v1.4.1 requires Go 1.25 or later.

Credits:

Thank you to Lê Minh Quân for reporting the issue.

Severity
7.1 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.4.0"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/modelcontextprotocol/go-sdk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.4.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33252"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-352"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-19T16:42:40Z",
    "nvd_published_at": "2026-03-24T00:16:30Z",
    "severity": "HIGH"
  },
  "details": "The Go SDK\u0027s Streamable HTTP transport accepted browser-generated cross-site `POST` requests without validating the `Origin` header and without requiring `Content-Type: application/json`. In deployments without Authorization, especially stateless or sessionless configurations, this allows an arbitrary website to send MCP requests to a local server and potentially trigger tool execution.\n\n#### Impact:\n\nA malicious website may have been able to send cross-site POST requests with `Content-Type: text/plain`, which due to CORS-safelisted properties would reach the MCP message handling without any CORS preflight barrier.\n\n#### Fix:\n\nThe SDK was modified to perform `Content-Type` header validation for POST requests and introduced a configurable protection for verifying the origin of the request in commit a433a83. Users are advised to update to v1.4.1 to use this additional protection.\n\nNote: v1.4.1 requires Go 1.25 or later.\n\n#### Credits:\n\nThank you to L\u00ea Minh Qu\u00e2n for reporting the issue.",
  "id": "GHSA-89xv-2j6f-qhc8",
  "modified": "2026-03-25T20:48:22Z",
  "published": "2026-03-19T16:42:40Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-89xv-2j6f-qhc8"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33252"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/go-sdk/commit/a433a831d6e5d5ac3b9e625a8095aa8eaa040dfc"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/modelcontextprotocol/go-sdk"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk"
}



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