WS-2026-0089
Published:September 28, 2026
Updated:October 07, 2026
In mcp (MCP Python SDK) 1.9.1 through 1.29.1 and 2.0.0a1 through 2.1.1, the OAuth client (mcp.client.auth) did not validate the authorization server metadata issuer on every discovery path and did not bind stored or pre-provisioned client credentials to their authorization server. A malicious or compromised MCP server could direct the client to a token endpoint of its choosing and receive the client_secret, authorization code and PKCE code_verifier (or a signed client assertion) meant for the real authorization server. Fixed in 1.30.0 and 2.2.0.
Affected Packages
mcp (CONDA):
Affected version(s) >=2.0.0 <2.2.0Fix Suggestion:
Update to version 2.2.0https://github.com/modelcontextprotocol/python-sdk.git (GITHUB):
Affected version(s) >=v2.0.0 <v2.2.0Fix Suggestion:
Update to version v2.2.0https://github.com/modelcontextprotocol/python-sdk.git (GITHUB):
Affected version(s) >=1.15.0 <v1.30.0Fix Suggestion:
Update to version v1.30.0mcp (PYTHON):
Affected version(s) >=1.9.1 <1.30.0Fix Suggestion:
Update to version 1.30.0mcp (PYTHON):
Affected version(s) >=2.0.0 <2.2.0Fix Suggestion:
Update to version 2.2.0Related Resources (4)
Do you need more information?
Contact UsCVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
NONE
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE
Weakness Type (CWE)
Insufficiently Protected Credentials