CVE-2026-32871: FastMCP is a Pythonic way to build MCP servers and clients

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CRITICAL 10.0REMOTEUPGRADE

CVE-2026-32871 is a critical-severity flaw (CVSS 10.0) affecting fastmcp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

FastMCP is a Pythonic way to build MCP servers and clients. Prior to version 3.2.0, the OpenAPIProvider in FastMCP exposes internal APIs to MCP clients by parsing OpenAPI specifications. The RequestDirector class is responsible for constructing HTTP requests to the backend service. A vulnerability exists in the _build_url() method. When an OpenAPI operation defines path parameters (e.g., /api/v1/users/{user_id}), the system directly substitutes p

Why this priority

Critical severity
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	10.0 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.9% (top 40%)
CISA exploited list	No
Weakness	CWE-918
Published	2026-04-02
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: jlowin

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-02 15:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

jlowin fastmcp UPGRADE

Affected: < 3.2.0

Fixed in: 3.2.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy fastmcp || rpm -q fastmcp || fastmcp --version

2. UPGRADE to 3.2.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fastmcp

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fastmcp

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Exact fixes by distribution

Python (pip) · fastmcp · FIXED · 3.2.0 · vulnerable: < 3.2.0 · source

pip install --upgrade "fastmcp>=3.2.0" pip show fastmcp

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: github.com/PrefectHQ/fastmcp/security/advisories/GHSA-vv7q-7jx5-f767

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-32871?

fastmcp: upgrade to 3.2.0. Exact commands for each OS are on this page.

Is CVE-2026-32871 being exploited?

CVE-2026-32871 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-32871 affect?

CVE-2026-32871 affects fastmcp. Severity is critical (CVSS 10.0). FastMCP is a Pythonic way to build MCP servers and clients. Prior to version 3.2.0, the OpenAPIProvider in FastMCP exposes internal APIs to MCP clients by parsing OpenAPI specifications. The RequestDirector class is responsible for construc

How urgent is CVE-2026-32871?

Priority 63/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

References

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