gcdRadar
archive/Patch now/AIR-2026-1491
closedclosed 23 Oct 2026Patch now2 Disclosed vulnerabilityAI

GHSA-vqqp-x5qm-5qp4: FastMCP OAuth client provider issuer binding vulnerability

fastmcp, fastmcp-slim

FastMCP client wrappers construct M2M OAuth providers without issuer binding, allowing untrusted servers to redirect client secrets. The vulnerability affects stable versions 4.0.0 through 4.1.1 and has been patched.

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

fix status
Fix status unknown
first report
23 Oct 2026
last update
23 Oct 2026

Timeline · 1

  1. 23 Oct 2026GHSA-vqqp-x5qm-5qp4: FastMCP MCP client wrappers construct M2M OAuth providers without issuer binding — client secret redirectable to attacker-advertised…

Sources · 1

Advisories and databases

  1. 2026-10-23
    GHSA-vqqp-x5qm-5qp4: FastMCP MCP client wrappers construct M2M OAuth providers without issuer binding — client secret redirectable to attacker-advertised…
    GitHub Advisory Database · github.com/advisories/GHSA-vqqp-x5qm-5qp4

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
ghsa-vqqp-x5qm-5qp4fastmcpoauthmcp
dates
happened 23 Oct 2026 · first reported 23 Oct 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 2026-10-24 05:11Z · updated 2026-10-24 05:11Z

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
# GHSA-vqqp-x5qm-5qp4: FastMCP OAuth client provider issuer binding vulnerability

https://gcdradar.vercel.app/incidents/ghsa-vqqp-x5qm-5qp4-fastmcp-oauth-client-provider-issuer-bin · AIR-2026-1491 · closed 2026-10-23

- Lane: Patch now
- Severity: 2 (Disclosed vulnerability)
- Fix status: Fix status unknown
- First reported: 2026-10-23
- AI role: Attack on AI
- Products: fastmcp, fastmcp-slim

## Summary

FastMCP client wrappers construct M2M OAuth providers without issuer binding, allowing untrusted servers to redirect client secrets. The vulnerability affects stable versions 4.0.0 through 4.1.1 and has been patched.

## What to do

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

## Latest updates

- 2026-10-23: GHSA-vqqp-x5qm-5qp4: FastMCP MCP client wrappers construct M2M OAuth providers without issuer binding — client secret redirectable to attacker-advertised… (https://github.com/advisories/GHSA-vqqp-x5qm-5qp4)

## Sources

- 2026-10-23 GitHub Advisory Database: GHSA-vqqp-x5qm-5qp4: FastMCP MCP client wrappers construct M2M OAuth providers without issuer binding — client secret redirectable to attacker-advertised… https://github.com/advisories/GHSA-vqqp-x5qm-5qp4

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

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