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Mcp Typescript SdkApplication · Lfprojects

CVE-2026-25536

HIGH · 7.1 CVSS v3.1 Published 2026-02-04
Fix available
A fix is available. Upgrade to 1.26.0 or later.
See remediation →
77/100
Remediation priority · High
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. From version 1.10.0 to 1.25.3, cross-client response data leak when a single McpServer/Server and transport instance is reused across multiple client connections, most commonly in stateless StreamableHTTPServerTransport deployments. This issue has been patched in version 1.26.0.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

The MCP TypeScript SDK versions 1.10.0 through 1.25.3 contain a vulnerability where response data can leak between different client connections when a single McpServer/Server and transport instance is reused across multiple clients. This is most commonly exploited in stateless StreamableHTTPServerTransport deployments where server instances are shared.

MitigationUpgrade the MCP TypeScript SDK to version 1.26.0 or later, which contains the patch for this vulnerability. Review any stateless deployments to ensure proper instance isolation per client connection.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Mcp Typescript SdkApplication
Affected:>= 1.10.0, < 1.26.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed MCP TypeScript SDK version
    Check your package.json or node_modules/@modelcontextprotocol/typescript-sdk/package.json for the version field, or run 'npm list @modelcontextprotocol/typescript-sdk'
    Affected if The installed version is >= 1.10.0 and < 1.26.0
  2. Determine if server instance is reused across connections
    Review your server initialization code to see if a single McpServer or Server instance is being reused for multiple client connections instead of creating a new instance per connection
    Affected if A single server instance handles multiple clients without per-connection instantiation
  3. Check for shared transport instances
    Examine your code to see if StreamableHTTPServerTransport is instantiated once and reused across different client connections
    Affected if One transport instance serves multiple clients
  4. Identify stateless deployment pattern
    Review your deployment configuration to determine if you are using StreamableHTTPServerTransport in a stateless manner (e.g., serverless function, containerized service with connection pooling)
    Affected if StreamableHTTPServerTransport is deployed statelessly with shared server instances

You are affected if your MCP TypeScript SDK version is between 1.10.0 and 1.25.3 AND you reuse a single server or transport instance across multiple client connections, particularly in stateless StreamableHTTPServerTransport deployments.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.26.0 or later
Fixed in 1.26.0
Interim mitigation

Upgrade the MCP TypeScript SDK to version 1.26.0 or later, which contains the patch for this vulnerability. Review any stateless deployments to ensure proper instance isolation per client connection.

Recommended fix High confidence

1.26.0

  1. Identify the current Mcp TypeScript SDK version in your package.json or package-lock.json
  2. Update the @modelcontextprotocol/server package version to 1.26.0 in your package.json dependencies
  3. Run 'npm update' or 'npm install @modelcontextprotocol/[email protected]' to install the fixed version
  4. Verify the installation was successful by checking the installed version
  5. Test your application to confirm the cross-client response data leak is resolved

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Mcp Typescript Sdk Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing4.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,540
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,464.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-25536 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
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