Disclosure summary
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.
Source-reported weakness categories
CWE-79
Source-specific records & product guidance
Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.
NIST National Vulnerability Database · NVD-CVE-2025-62800
Open original source · Updated Oct 08, 2026
Only CPE matches marked vulnerable=true are indexed. AND/OR platform conditions must be checked in the original NVD record.
| Vendor | Product / association | Version / bounds |
|---|---|---|
| jlowin | fastmcp | * {"versionEndExcluding":"2.13.0"} |
Original records & references
- NIST NVD record
- CVE Program record
- github.com — Exploit, Third Party Advisory
- github.com — Exploit, Third Party Advisory
PUBLISHED 2025-10-28T18:15:36-04:00
MODIFIED 2026-10-08T07:10:00-04:00
INGESTED 2026-10-08T12:35:13-04:00