gcdRadar
archive/Patch now/AIR-2026-0536
closedclosed 31 Mar 2026Patch now2 Disclosed vulnerabilityAI

CVE-2026-27124: FastMCP OAuth Proxy Lacks Consent Verification

FastMCP

A missing consent verification flaw in FastMCP's OAuth Proxy callback facilitates confused deputy vulnerabilities. The issue arises when combining previously authorized OAuth clients with unvalidated authorization codes.

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
8.2
EPSS
<0.01 · top 89% · 2026-11-13
EPSS scores by FIRST
fix status
Fix status unknown
first report
31 Mar 2026
last update
31 Mar 2026
CVE ids
CVE-2026-27124other records

Timeline · 1

  1. 31 Mar 2026CVE-2026-27124: FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities

Sources · 1

Advisories and databases

  1. 2026-03-31
    CVE-2026-27124: FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities
    GitHub Advisory Database · github.com/advisories/GHSA-rww4-4w9c-7733

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
confused-deputy
dates
happened 31 Mar 2026 · first reported 31 Mar 2026
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-2026-27124: FastMCP OAuth Proxy Lacks Consent Verification

https://gcdradar.vercel.app/incidents/cve-2026-27124-fastmcp-oauth-proxy-lacks-consent-verificatio · AIR-2026-0536 · closed 2026-03-31

- Lane: Patch now
- Severity: 2 (Disclosed vulnerability)
- Fix status: Fix status unknown
- First reported: 2026-03-31
- AI role: Attack on AI
- Products: FastMCP
- CVE ids: CVE-2026-27124
- CVSS: 8.2

## Summary

A missing consent verification flaw in FastMCP's OAuth Proxy callback facilitates confused deputy vulnerabilities. The issue arises when combining previously authorized OAuth clients with unvalidated authorization codes.

## What to do

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

## Latest updates

- 2026-03-31: CVE-2026-27124: FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities (https://github.com/advisories/GHSA-rww4-4w9c-7733)

## Sources

- 2026-03-31 GitHub Advisory Database: CVE-2026-27124: FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities https://github.com/advisories/GHSA-rww4-4w9c-7733

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

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