CVE-2025-62800

Name: CVE-2025-62800
Creator: NVD / NIST
Published: 2025-10-28T22:15:36.983+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 0.25%

Last modified Jun 17, 2026

CVE-2025-62800 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. 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. EPSS estimates a 0.25% chance of exploitation in the next 30 days.

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

6.1/10

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

CVSS 4.0

5.3/10

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.25%

16.2th percentile

Probability of exploitation in the next 30 days. Learn more

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: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2025-62800?

How severe is CVE-2025-62800?

CVE-2025-62800 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.25% probability of exploitation in the next 30 days.

How do I fix CVE-2025-62800?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2025-62800?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST