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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.

PUBLISHED Reserved 2025-10-22 | Published 2025-10-28 | Updated 2025-10-29 | Assigner GitHub_M




MEDIUM: 5.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Problem types

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Product status

< 2.13.0
affected

References

github.com/...astmcp/security/advisories/GHSA-mxxr-jv3v-6pgc

cve.org (CVE-2025-62800)

nvd.nist.gov (CVE-2025-62800)

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