Not ratedCVE-2026-111770

    Server: Race Condition (CVE-2026-111770)

    Published Sources: OSV, Hersteller

    What is affected, what to do

    Update Server to version 2.3.0.

    Affected
    • Server *..>= 2.0.0, < 2.3.0
    • Server 2.0.0..*
    Fixed in
    • Server 2.3.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

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    Priority

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    CVSS v3

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    EPSS score

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    Severity
    Not rated
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    30.00 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

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    no public PoC known
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

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    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-362

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

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    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

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    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

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    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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.

    Source: OSV (Open Source Vulnerabilities), GitHub Security Advisories

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    npm@modelcontextprotocol/server
    • 2.0.0
    • >= 2.0.0, < 2.3.0
    • 2.3.0
    • 2.3.0

    Weakness classes (CWE)

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

      Class

      The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

      Entry at MITRE CWE-362

    References & sources

    • github.commodelcontextprotocol/typescript-sdk/security/advisories/GHSA-jm…web
    • github.commodelcontextprotocol/typescript-sdk/pull/2918web
    • github.commodelcontextprotocol/typescript-sdk/commit/84804c22e45a662675a1…web
    • github.commodelcontextprotocol/typescript-sdkpackage
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