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.
Exploitability
AV:NAC:HPR:LUI:NScope
S:UImpact
C:HI:HA:N6.8/CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:NAccess Control