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Vulnerabilities

Vulnerability · CVE-2026-32871

FastMCP is a Pythonic way to build MCP servers and clients.

Published Apr 2, 2026 · catalog updated Jul 15, 2026 · FastMCP is a Pythonic

Check if you run it

No confirmed exploitation is on record for CVE-2026-32871. EPSS is 1.37%. Act only if a listed version of FastMCP is a Pythonic is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (FastMCP is a Pythonic).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Critical10.0
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
1.37%
Remediation
Advisory link
Affected products
cpe jlowin/fastmcp

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 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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe jlowin/fastmcpversion unspecified

How to fix CVE-2026-32871

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-32871. EPSS is 1.37%. Act only if a listed version of FastMCP is a Pythonic is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-918: Server-Side Request Forgery (SSRF). EPSS 1.37%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 2, 2026 · NIST NVD

    Detected

    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/u

  2. Jul 15, 2026 · NIST NVD

    Updated

    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/u

Sources

  • CVE.orgVulnerability recordCVE-2026-32871

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-32871

    30-day exploitation probability 1.4%

    first.org
  • NIST NVDVulnerability recordCVE-2026-32871

    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 servic

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.