Read the docs
TI-2026-21575 Aliases CVE-2026-27124GHSA-rww4-4w9c-7733

FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities

Priority HIGH 75CWE-441Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
None · High · None
Fix status
Partial Red Hat: 3 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat.

Summary

FastMCP is the standard framework for building MCP applications. Prior to version 3.2.0, while testing the GitHubProvider OAuth integration, which allows authentication to a FastMCP MCP server via a FastMCP OAuthProxy using GitHub OAuth, it was discovered that the FastMCP OAuthProxy does not properly validate the user's consent upon receiving the authorization code from GitHub. In combination with GitHub’s behavior of skipping the consent page for previously authorized clients, this introduces a Confused Deputy vulnerability. This issue has been patched in version 3.2.0.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00211 11th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Partial fastmcp (jlowin): 3.2.0fastmcp (PyPI): 3.2.0Red Hat: 3 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
jlowinfastmcpbefore 3.2.03.2.0Patch availableCNA
—fastmcp (PyPI)before 3.2.03.2.0Patch availableGHSA-rww4-4w9c-7733
  • fastmcp Vendorjlowin Affected before 3.2.0 Fixed in 3.2.0 Patch available CNA
  • fastmcp (PyPI) Vendor— Affected before 3.2.0 Fixed in 3.2.0 Patch available GHSA-rww4-4w9c-7733

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:*before 3.2.0Vulnerablejlowin
  • cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:* Versions before 3.2.0 Vulnerable ·jlowin

Remediation

  • Fix · CNA fastmcp (jlowin) Fixed in 3.2.0
  • Fix · GHSA-rww4-4w9c-7733 fastmcp (PyPI) Fixed in 3.2.0 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Developer Hub 1AffectedNo fix yet: Fix deferred
Red Hat OpenShift AI (RHOAI)AffectedNo fix yet: Fix deferred
Red Hat Satellite 6AffectedNo fix yet: Fix deferred

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-27124
  2. 2026-10-03 Alias added: GHSA-rww4-4w9c-7733
  3. 2026-10-27 Affected versions changed · Red Hat

References

Exploit 1

Advisory 1

Other 2

  • TI-2026-25332 FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability CVSS 4.0CRITICAL 10.0
  • TI-2025-39774 FastMCP has a Command Injection vulnerability - Gemini CLI CVSS 3.1HIGH 7.8
  • TI-2025-42650 FastMCP OAuth Proxy token reuse across MCP servers CVSS 4.0HIGH 7.4
  • TI-2025-38984 FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name CVSS 4.0MEDIUM 5.4
  • TI-2025-38983 FastMCP vulnerable to reflected XSS in client's callback page CVSS 4.0MEDIUM 5.3

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences