Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource server

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-116684
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-27 20:17:13 UTC
Updated2026-10-27 20:17:13 UTC
DescriptionThe Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.10.0 until 1.30.0 and 2.2.0, server-side bearer authentication configured through AuthSettings with token_verifier accepts a valid token issued for another service when the authorization server serves multiple resources and the TokenVerifier does not independently validate the aud audience. This resource-confusion flaw lets a token holder authenticate to the wrong MCP server and exercise that token's resulting access. This issue is fixed in versions 1.30.0 and 2.2.0.

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 Python-sdk affected >= 1.10.0, < 1.30.0 Not specified
CNA Modelcontextprotocol Python-sdk affected >= 2.0.0, < 2.2.0 Not specified

References

ReferenceSourceLinkTags
github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/commit/0c9136841ff092987a2070... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/pull/3451 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/commit/8c2fa6eabacde869d75568... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-w4fh... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/pull/3447 [email protected] github.com
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