CVE-2025-62800

MEDIUM

fastmcp < 2.13.0 - Reflected Cross-Site Scripting in OAuth Client Callback Page

Title source: llm

Description

FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0 have a reflected cross-site scripting vulnerability in the OAuth client callback page (oauth_callback.py) where unescaped user-controlled values are inserted into the generated HTML, allowing arbitrary JavaScript execution in the callback server origin. The issue is fixed in version 2.13.0.

References (1)

Core 1

Core References

Exploit, Third Party Advisory x_refsource_confirm

https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc

Scores

CVSS v3 6.1

EPSS 0.0005

EPSS Percentile 15.3%

Attack Vector NETWORK

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CISA SSVC

Vulnrichment

Exploitation poc

Automatable no

Technical Impact partial

Details

CWE

CWE-79

Status published

Products (2)

jlowin/fastmcp < 2.13.0

pypi/fastmcp 0 - 2.13.0PyPI

Published Oct 28, 2025

Tracked Since Feb 18, 2026