CVE-2026-116684
Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource server
- State
- Published
- Severity
- 6.8 Medium
- Published
- Oct 27, 2026
- Updated
- Oct 27, 2026
- Reserved
- Oct 26, 2026
Description
The 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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 6.8 Medium | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N | GitHub_M |
Weaknesses
- CWE-863 Incorrect Authorization
Affected Products
| Product | Versions |
|---|---|
python-sdkmodelcontextprotocol |
|
References
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-w4fh-qvv9-3v23
- https://github.com/modelcontextprotocol/python-sdk/pull/3447
- https://github.com/modelcontextprotocol/python-sdk/pull/3451
- https://github.com/modelcontextprotocol/python-sdk/commit/0c9136841ff092987a20700ff9c2c9789bda2f40
- https://github.com/modelcontextprotocol/python-sdk/commit/8c2fa6eabacde869d75568e33b9d466b58c2f512
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0
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