CVE-2025-62800

MediumCVSS 6.1/10Last modified Oct 8, 2026

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.

Metrics

CVSS 3.1 6.1/10CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Weakness enumeration

CWE-79

Affected software

Vendor	Product	Versions
jlowin	fastmcp	< 2.13.0

References

https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgcExploit, Third Party Advisory
https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgcExploit, Third Party Advisory

Timeline

Published: Oct 28, 2025
Last modified: Oct 8, 2026
NVD status: Analyzed

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