CVE-2025-69196
Received Received - Intake
OAuth Token Misissuance in FastMCP Server Before

Publication date: 2026-03-16

Last updated on: 2026-03-18

Assigner: GitHub, Inc.

Description
FastMCP is the standard framework for building MCP applications. Prior to version 2.14.2, the server does not properly respect the resource parameter submitted by the client in the authorization and token request. Instead of issuing the token explicitly for the MCP server, the token is issued for the base_url passed to the OAuthProxy during initialization. This issue has been patched 2.14.2.
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Meta Information
Published
2026-03-16
Last Modified
2026-03-18
Generated
2026-06-16
AI Q&A
2026-03-16
EPSS Evaluated
2026-06-15
NVD
CVE-2025-69196
EUVD
EUVD-2025-208759
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
jlowin fastmcp to 2.14.2 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-863 The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
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Executive Summary

CVE-2025-69196 is a vulnerability in the FastMCP OAuth Proxy prior to version 2.14.2 where the server does not properly respect the resource parameter submitted by the client during authorization and token requests.

Instead of issuing tokens explicitly for the specific MCP server requested by the client, the OAuth Proxy issues tokens based on its own base_url configured during initialization. This means the tokens lack information about the intended MCP server resource.

As a result, MCP servers cannot verify if a token was legitimately issued for them, violating OAuth specifications and enabling attackers to set up malicious MCP servers that can steal tokens and reuse them to access other legitimate MCP servers.

Impact Analysis

This vulnerability allows an attacker to steal OAuth tokens by tricking users into authenticating with a malicious MCP server.

Because the tokens are not bound to a specific MCP server, the attacker can reuse stolen tokens to gain unauthorized access to other legitimate MCP servers that rely on the same OAuth Proxy.

This compromises the authentication integrity of MCP servers, potentially exposing sensitive tools and resources to unauthorized parties.

Compliance Impact

I don't know

Detection Guidance

I don't know

Mitigation Strategies

To mitigate this vulnerability, you should upgrade FastMCP to version 2.14.2 or later, where the issue has been fixed.

The fix involves modifying the OAuth Proxy to issue tokens specifically for the MCP server indicated by the `resource` parameter in the authorization URL. This ensures tokens are bound to the intended resource and prevents token theft and reuse across MCP servers.

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