Live › vulnerability › CVE-2026-111770
Go to dashboardThe MCP TypeScript server SDK matched responses to HTTP clients by JSON-RPC id alone, so when one transport or server instance was shared, one client could receive another client's responses and notifications. An attacker who can reach the endpoint can read other clients' MCP traffic.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 19:11 UTC. All times on this page are UTC.
| Product | Ecosystem | Affected | Fixed in |
|---|
| @modelcontextprotocol/server | npm | >= 2.0.0, < 2.3.0 | 2.3.0 |
npm ls @modelcontextprotocol/server Affected versions are @modelcontextprotocol/server 2.0.0 through 2.2.02.3.0 or later, then change code so a new McpServer and transport are built per request, per session (with sessionIdGenerator), or via a createMcpHandler() factoryEach row is the first time that source carried this signal. The analyst’s rows are its own findings.
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.
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@modelcontextprotocol/sdk 1.26.0 and laterUpgrade 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.McpServer and a new transport inside the request handler.sessionIdGenerator and keep one McpServer and one transport per session.If you cannot upgrade yet, the same change fixes affected versions.
This page as .md · .json · in your agent: get_signal("CVE-2026-111770")
GitHub Advisory Database, CC-BY 4.0. Posts quoted belong to their authors.