Auth bypass in Modelcontextprotocol Python-Sdk
CVE-2026-116684
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.
Vulnerability class: Broken Access Control
Published .
CVSS v3 metric
CVSS v3 base score 6.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Modelcontextprotocol Python-Sdk — versions >= 1.10.0, < 1.30.0, >= 2.0.0, < 2.2.0
Weakness classification (CWE)
References
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-w4fh-qvv9-3…
- github.com/modelcontextprotocol/python-sdk/pull/3447
- github.com/modelcontextprotocol/python-sdk/pull/3451
- github.com/modelcontextprotocol/python-sdk/commit/0c9136841ff092987a20700ff9c2c…
- github.com/modelcontextprotocol/python-sdk/commit/8c2fa6eabacde869d75568e33b9d4…
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
- github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0
Frequently asked questions
- What is CVE-2026-116684?
- CVE-2026-116684 is a medium-severity vulnerability in Modelcontextprotocol Python-Sdk, classified under Incorrect Authorization. CVSS score: 6.8/10. Published 2026-10-27.
- How severe is CVE-2026-116684?
- Medium severity. CVSS v3 base score is 6.8 out of 10.