gcdRadar
archive/Patch now/AIR-2025-0360
closedclosed 29 Oct 2025Patch now2 Disclosed vulnerabilityAI

CVE-2025-62800: FastMCP reflected XSS in oauth callback page

FastMCP

A reflected cross-site scripting vulnerability was discovered in FastMCP due to improper escaping of user-controlled content in the OAuth callback page. No active exploitation has been reported.

disclosed CVENo confirmed exploitation, so this record is tracked as a disclosed vulnerability and not counted as an incident. It moves into the counts if CISA or the vendor confirms exploitation. Why

CVSS
5.3
EPSS
<0.01 · top 80% · 2026-11-13
EPSS scores by FIRST
fix status
Fix status unknown
first report
29 Oct 2025
last update
29 Oct 2025
CVE ids
CVE-2025-62800other records

Timeline · 1

  1. 29 Oct 2025CVE-2025-62800: FastMCP vulnerable to reflected XSS in client's callback page

Sources · 1

Advisories and databases

  1. 2025-10-29
    CVE-2025-62800: FastMCP vulnerable to reflected XSS in client's callback page
    GitHub Advisory Database · github.com/advisories/GHSA-mxxr-jv3v-6pgc

Titles and links belong to their publishers. The summary above is written by gcdRadar in its own words; data is CC BY-SA 4.0.

Classification

lane
Patch now
AI role
Attack on AI
categories
Infrastructure vulnerability
severity
2 · Disclosed vulnerability
fix status
Fix status unknown
targets
Framework / tooling
owasp llm top 10
LLM03:2025 Supply Chain
mitre atlas
no technique for these categories
tags
xssmcp
dates
happened 29 Oct 2025 · first reported 29 Oct 2025
origin
GitHub Advisory Database
Vulnerability record from NVD / the GitHub Advisory Database. This product uses the NVD API but is not endorsed or certified by the NVD.
record
confidence 0.95 · created 2026-10-18 07:00Z · updated 2026-10-18 07:00Z

Lane, AI role, categories and severity come from the classifier; the OWASP and ATLAS rows are derived from the categories. How these are assigned

Copy a brief

This record as a short Markdown brief, for a ticket, a chat or a coding agent.

the brief as text
# CVE-2025-62800: FastMCP reflected XSS in oauth callback page

https://gcdradar.vercel.app/incidents/cve-2025-62800-fastmcp-reflected-xss-in-oauth-callback-page · AIR-2025-0360 · closed 2025-10-29

- Lane: Patch now
- Severity: 2 (Disclosed vulnerability)
- Fix status: Fix status unknown
- First reported: 2025-10-29
- AI role: Attack on AI
- Products: FastMCP
- CVE ids: CVE-2025-62800
- CVSS: 5.3

## Summary

A reflected cross-site scripting vulnerability was discovered in FastMCP due to improper escaping of user-controlled content in the OAuth callback page. No active exploitation has been reported.

## What to do

No action recorded; read the sources below and the vendor's advisory.

## Latest updates

- 2025-10-29: CVE-2025-62800: FastMCP vulnerable to reflected XSS in client's callback page (https://github.com/advisories/GHSA-mxxr-jv3v-6pgc)

## Sources

- 2025-10-29 GitHub Advisory Database: CVE-2025-62800: FastMCP vulnerable to reflected XSS in client's callback page https://github.com/advisories/GHSA-mxxr-jv3v-6pgc

Verify against the vendor's advisory before changing production. Data CC BY-SA 4.0, https://gcdradar.vercel.app.

Related

  1. closed
    FastMCP FastMCP auth integration confused deputy issue

    Patch now · Disclosed · since 29 Oct 2025

    AI
  2. closed5.4
    FastMCP CVE-2025-62801: FastMCP command injection in Cursor installer

    Patch now · Disclosed · since 29 Oct 2025 · CVE-2025-62801

    AI
  3. closed10.0
    FastMCP CVE-2026-32871: FastMCP OpenAPI Provider SSRF and Path Traversal

    Patch now · Disclosed · since 31 Mar 2026 · CVE-2026-32871

    AI
  4. closed6.7
    FastMCP CVE-2025-64340: FastMCP Command Injection via Server Names

    Patch now · Disclosed · since 31 Mar 2026 · CVE-2025-64340

    AI
  5. closed8.2
    FastMCP CVE-2026-27124: FastMCP OAuth Proxy Lacks Consent Verification

    Patch now · Disclosed · since 31 Mar 2026 · CVE-2026-27124

    AI
  6. closed7.4
    FastMCP CVE-2025-69196: FastMCP OAuth Proxy Token Reuse

    Patch now · Disclosed · since 16 Mar 2026 · CVE-2025-69196

    AI