Answer in brief
CVE-2026-111770 records a High severity (CVSS 7.7) vulnerability in MCP TypeScript server SDK: Shared transport or server instances delivered one HTTP client's messages to another. The current sources do not mark it as known exploited. The current feed maps @modelcontextprotocol/server (npm). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps @modelcontextprotocol/server (npm). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| @modelcontextprotocol/servernpm | >=2.0.0,<2.3.0 | 2.3.0 |
Published upstream
Oct 20, 2026
Evidence: source:ghsa:source_dates:source-dates:recordSource modified
Oct 20, 2026
Evidence: source:ghsa:source_dates:source-dates:recordFirst seen by HOL
Oct 20, 2026
### 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.
Quoted source text, attributed separately from HOL analysis.