TypeScript SDK Vulnerability in Model Context Protocol by ModelContextProtocol

CVE-2026-111770

What is CVE-2026-111770?

The Model Context Protocol TypeScript SDK, particularly versions 2.0.0 to 2.3.0 of the @modelcontextprotocol/server, contains a cross-client delivery vulnerability. In scenarios where multiple clients utilize a single stateless HTTP transport or server instance, there's a risk of delivering responses and notifications to incorrect clients. This misrouting occurs because messages are identified solely by the JSON-RPC request identifier, which is reset to zero for each client, leading to potential collisions during standard operations. The vulnerability can be exploited if the HTTP endpoint is shared across multiple clients, and the server or transport is instantiated only once at startup rather than per request. Users must upgrade to @modelcontextprotocol/server version 2.3.0 to mitigate this issue, which may require code changes due to instance reuse failures. Notably, stdio servers and factory-created per-call servers remain unaffected by this flaw.

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