---
title: "CVE-2026-32871: FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-32871/
description: "CVE-2026-32871 (fastmcp (PyPI)): FastMCP is a Pythonic way to build MCP servers and clients. Prior to version 3.2.0, the OpenAPIProvider in FastMCP exposes…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-04-02
date_modified: 2026-07-15
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-32871"
kev: false
cvss: 10
epss: 0.01369
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-32871: FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 1.4% , percentile 72: FIRST’s model estimates a 1.4% chance of exploitation activity in the next 30 days, higher than 72% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes fastmcp (PyPI) < 3.2.0, fixed in 3.2.0 . Check your lockfile, including transitive dependencies.

## What it is

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 buildurl() method. When an OpenAPI operation defines path parameters (e.g., /api/v1/users/{userid}), the system directly substitutes parameter values into the URL template string without URL-encoding. Subsequently, urllib.parse.urljoin() resolves the final URL. Since urljoin() interprets ../ sequences as directory traversal, an attacker controlling a path parameter can perform path traversal attacks to escape the intended API prefix and access arbitrary backend endpoints. This results in authenticated SSRF, as requests are sent with the authorization headers configured in the MCP provider. This issue has been patched in version 3.2.0.

## Affected packages

- PyPI `fastmcp` < 3.2.0 → fixed: 3.2.0

## Affected products (CVE record)

- PrefectHQ fastmcp: < 3.2.0

## Severity

- GitHub_M CVSS 4.0: 10 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`
- redhat-SADP CVSS 3.1: 8.5 `CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H`
- GitHub CVSS 4.0: 10.0 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 1.37% probability of exploitation activity in the next 30 days; percentile 72.

## Sources

- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:36350)
- [GitHub Advisory GHSA-vv7q-7jx5-f767](https://github.com/advisories/GHSA-vv7q-7jx5-f767)
- [CVE.org record CVE-2026-32871](https://www.cve.org/CVERecord?id=CVE-2026-32871)
- [NVD entry CVE-2026-32871](https://nvd.nist.gov/vuln/detail/CVE-2026-32871)
- [github.com](https://github.com/PrefectHQ/fastmcp/security/advisories/GHSA-vv7q-7jx5-f767)
- [github.com](https://github.com/PrefectHQ/fastmcp/pull/3507)
- [github.com](https://github.com/PrefectHQ/fastmcp/commit/40bdfb6b1de0ce30609ee9ba5bb95ecd04a9fb71)
- [github.com](https://github.com/PrefectHQ/fastmcp/releases/tag/v3.2.0)
- [access.redhat.com](https://access.redhat.com/security/cve/CVE-2026-32871)
- [RHBZ#2454434](https://bugzilla.redhat.com/show_bug.cgi?id=2454434)
- [security.access.redhat.com](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-32871.json)

---
Source page: https://erroneo.us/security/cve/CVE-2026-32871/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt