---
id: CVE-2025-62800
title: FastMCP is the standard framework for building MCP applications
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 ar…
severity: medium
cvss: 6.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'
cwe:
  - CWE-79
vendor: jlowin
product: fastmcp
affected:
  - fastmcp < 2.13.0
patched:
  - fastmcp 2.13.0
published: '2025-10-28'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T11:10:00.250'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-62800'
references:
  - url: 'https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc'
    label: security-advisories@github.com
  - url: 'https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-62800'
  - url: 'https://github.com/jlowin/fastmcp/pull/2090'
  - url: >-
      https://github.com/jlowin/fastmcp/commit/2a20f54617a37213ed83894a8c2f0ac38a2e83a3
  - url: 'https://github.com/jlowin/fastmcp'
tags:
  - nvd
  - osv
  - pip
epss: 0.00276
epssPercentile: 0.19938
aliases:
  - GHSA-mxxr-jv3v-6pgc
  - PYSEC-2026-1364
ecosystem: pip
ingestedAt: '2026-07-08T18:25:51.476Z'
---

## Overview

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.

## Affected

- `fastmcp < 2.13.0`

## Remediation

Upgrade past the affected range:

- `fastmcp 2.13.0`

## Package advisory (CVE-2025-62800)

Affected packages:

- `fastmcp < 2.13.0`

Patched in:

- `fastmcp 2.13.0`

Source: https://osv.dev/vulnerability/GHSA-mxxr-jv3v-6pgc