Vulnerability-Lookup

CVE-2026-111770 (GCVE-0-2026-111770)

Vulnerability from cvelistv5 – Published: 2026-11-05 21:28 – Updated: 2026-11-05 21:44

Title

Model Context Protocol TypeScript SDK: Shared transport or server instances delivered one HTTP client's messages to another

Summary

The Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 2.0.0 until 2.3.0 in @modelcontextprotocol/server, applications that shared one stateless HTTP transport or one McpServer or Server instance among multiple clients could deliver responses and notifications to the wrong client. The affected surface is an MCP server reached over HTTP by multiple clients. The trigger is reuse of one stateless transport or server instance. Messages were associated with a connection using only the JSON-RPC request identifier. SDK clients start request identifiers at zero, so collisions occur in normal operation. Cross-client delivery exposes one client's responses and notifications to another client. The issue requires an HTTP endpoint reachable by more than one client and an application that constructs the server or transport once at startup instead of once per request or session. stdio servers and factory-created per-call servers are not affected. Upgrading causes reused instances to fail and therefore requires an application code change. This issue is fixed in @modelcontextprotocol/server 2.3.0.

Severity

7.7 (High)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-11-05 21:44 UTC

CWE

CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 8081 records in the last 180 days details

References

5 references

URL	Tags
https://github.com/modelcontextprotocol/typescrip…	x_refsource_CONFIRM
https://github.com/modelcontextprotocol/typescrip…	x_refsource_MISC
https://github.com/modelcontextprotocol/typescrip…	x_refsource_MISC
https://github.com/modelcontextprotocol/typescrip…	x_refsource_MISC
https://github.com/modelcontextprotocol/typescrip…	x_refsource_MISC

Impacted products

2 products

Vendor	Product	Version	CPE status
modelcontextprotocol	typescript-sdk	Affected: < 1.32.0	guessed
@modelcontextprotocol	server	Affected: >= 2.0.0, < 2.3.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-111770

Vulnerability from fkie_nvd - Published: 2026-11-05 22:17 - Updated: 2026-11-05 22:17

Severity

7.7 (High) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/commit/84804c22e45a662675a198f853b7f00063838a8d
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/pull/2918
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/1.32.0
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontextprotocol/server@2.3.0
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-jm63-cq47-j5jp

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-362"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

GHSA-JM63-CQ47-J5JP

Vulnerability from github – Published: 2026-10-20 20:07 – Updated: 2026-10-20 20:07

Summary

MCP TypeScript server SDK: Shared transport or server instances delivered one HTTP client's messages to another

Details

Summary

In affected versions, an MCP server reached over HTTP could deliver one client's responses and notifications to another client. This happened when clients shared one stateless transport, or one McpServer or Server instance.

Messages were matched to a connection by JSON-RPC id alone. SDK clients number requests from 0, so ids collide in normal use.

Am I affected?

Yes, if more than one client can reach your HTTP endpoint and your code creates the transport or the server once at startup, instead of once per request or per session. Until this release, the README examples of @modelcontextprotocol/hono, express, fastify and node showed that pattern.

Affected versions: @modelcontextprotocol/server 2.0.0 through 2.2.0.

Not affected:

createMcpHandler() with a factory that builds a new server on every call
stdio servers
@modelcontextprotocol/sdk 1.26.0 and later

Fix

Upgrade to @modelcontextprotocol/server 2.3.0 or later.

You also need to change your code. The SDK now refuses to be shared, so an affected app fails requests after upgrading: a second connect() rejects with ALREADY_CONNECTED, and a stateless transport rejects its second request.

Change to one of these:

createMcpHandler(): pass a factory that builds a new McpServer on every call.
Per request: build a new McpServer and a new transport inside the request handler.
Per session: set sessionIdGenerator and keep one McpServer and one transport per session.

If you cannot upgrade yet, the same change fixes affected versions.

Severity

7.7 (High)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@modelcontextprotocol/server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-111770"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-362"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-20T20:07:29Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nIn affected versions, an MCP server reached over HTTP could deliver one client\u0027s responses and notifications to another client. This happened when clients shared one stateless transport, or one `McpServer` or `Server` instance.\n\nMessages were matched to a connection by JSON-RPC `id` alone. SDK clients number requests from 0, so ids collide in normal use.\n\n### Am I affected?\nYes, if more than one client can reach your HTTP endpoint and your code creates the transport or the server once at startup, instead of once per request or per session. Until this release, the README examples of `@modelcontextprotocol/hono`, `express`, `fastify` and `node` showed that pattern.\n\nAffected versions: `@modelcontextprotocol/server` 2.0.0 through 2.2.0.\n\nNot affected:\n\n- `createMcpHandler()` with a factory that builds a new server on every call\n- stdio servers\n- `@modelcontextprotocol/sdk` 1.26.0 and later\n\n### Fix\nUpgrade to `@modelcontextprotocol/server` 2.3.0 or later.\n\n**You also need to change your code.** The SDK now refuses to be shared, so an affected app fails requests after upgrading: a second `connect()` rejects with `ALREADY_CONNECTED`, and a stateless transport rejects its second request.\n\nChange to one of these:\n\n- **`createMcpHandler()`:** pass a factory that builds a new `McpServer` on every call.\n- **Per request:** build a new `McpServer` and a new transport inside the request handler.\n- **Per session:** set `sessionIdGenerator` and keep one `McpServer` and one transport per session.\n\nIf you cannot upgrade yet, the same change fixes affected versions.",
  "id": "GHSA-jm63-cq47-j5jp",
  "modified": "2026-10-20T20:07:29Z",
  "published": "2026-10-20T20:07:29Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-jm63-cq47-j5jp"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/pull/2918"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/commit/84804c22e45a662675a198f853b7f00063838a8d"
    },
    {
      "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:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "MCP  TypeScript server SDK: Shared transport or server instances delivered one HTTP client\u0027s messages to another"
}

Sightings

Author	Source	Type	Date	Other

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Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
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Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Action not permitted

CVE-2026-111770 (GCVE-0-2026-111770)

FKIE_CVE-2026-111770

GHSA-JM63-CQ47-J5JP

Summary

Am I affected?

Fix

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