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Vulnerability · Published Mar 16, 2026 · Assigned by GitHub_M

CVE-2025-69196FastMCP OAuth Proxy token reuse across MCP servers

High 7.4

In plain English

A high-severity incorrect authorization in fastmcp from jlowin. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.4High
Exploit odds (30 days)0.4%top 67.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPIfastmcp2.14.2GHSA-5h2m-4q8j-pqpj
PyPIfastmcp2.14.2PYSEC-2026-2474

Affected products (as reported)

VendorProductVersions
jlowin fastmcp < 2.14.2

Weakness: CWE-863, CWE-1220 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

References