Model Context Protocol TypeScript SDK: Server bearer authentication accepted tokens issued for another service

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-111771
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-05 21:18:35 UTC
Updated2026-11-05 21:18:35 UTC
DescriptionThe Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 1.6.0 until 1.32.0 in @modelcontextprotocol/sdk, from 2.0.0 until 2.3.0 in @modelcontextprotocol/server, from 2.0.0 until 2.0.2 in @modelcontextprotocol/express, and from 2.0.0 until 2.3.1 in @modelcontextprotocol/server-legacy, server-side bearer authentication could accept a valid access token issued for a different service because the SDK did not enforce the token audience. The affected surface is server-side HTTP bearer authentication. The trigger is a valid token whose audience names another service. The authorization server must issue tokens for multiple services, and the application's verifyAccessToken() must not independently validate aud. Applications already validating aud inside verifyAccessToken() are not affected. An attacker with a token for another service could authenticate to the MCP server and obtain the confidentiality and integrity capabilities granted to an authenticated caller. Upgrading alone leaves the new audience validation disabled. Operators must enable audience validation and provide the token audience together. Enabling only the expected audience check causes every request to receive HTTP 401. This issue is fixed in @modelcontextprotocol/sdk 1.32.0, @modelcontextprotocol/server 2.3.0, @modelcontextprotocol/express 2.0.2, and @modelcontextprotocol/server-legacy 2.3.1.

Risk And Classification

Primary CVSS: v3.1 6.8 MEDIUM from [email protected]

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

Problem Types: CWE-863 | CWE-863 CWE-863: Incorrect Authorization

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
3.1CNADECLARED6.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Modelcontextprotocol Typescript-sdk affected >= 1.6.0, < 1.32.0 Not specified
CNA @modelcontextprotocol Sdk affected >= 1.6.0, < 1.32.0 Not specified
CNA @modelcontextprotocol Server affected >= 2.0.0, < 2.3.0 Not specified
CNA @modelcontextprotocol Express affected >= 2.0.0, < 2.0.2 Not specified
CNA @modelcontextprotocol Server-legacy affected >= 2.0.0, < 2.3.1 Not specified

References

ReferenceSourceLinkTags
github.com/modelcontextprotocol/typescript-sdk/commit/5a1867390b91b8836f... [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontex... [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/releases/tag/1.32.0 [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/pull/2952 [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/commit/40f8f4e229d963cd7f... [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontex... [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-... [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/commit/5a0724d14cf34a27a3... [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/pull/2929 [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontex... [email protected] github.com
github.com/modelcontextprotocol/typescript-sdk/pull/2930 [email protected] github.com
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