What is CVE-2025-64340?

CVE-2025-64340 is a medium-severity vulnerability in Jlowin Fastmcp, classified under OS Command Injection. CVSS score: 6.7/10. Published 2026-04-03.

How severe is CVE-2025-64340?

Medium severity. CVSS v3 base score is 6.7 out of 10.

RCE in Jlowin Fastmcp

CVE-2025-64340

FastMCP is the standard framework for building MCP applications. Prior to version 3.2.0, server names containing shell metacharacters (e.g., &) can cause command injection on Windows when passed to fastmcp install claude-code or fastmcp in…

Vulnerability class: Command Injection (OS Command Injection)

EPSS: 0.000 (1.1th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.7 (Medium). Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H.

Affected products

Jlowin Fastmcp — versions < 3.2.0

Weakness classification (CWE)

CWE-78 — OS Command Injection

References

https://github.com/PrefectHQ/fastmcp/security/advisories/GHSA-m8x7-r2rg-vh5g (x_refsource_CONFIRM)
https://github.com/PrefectHQ/fastmcp/pull/3522 (x_refsource_MISC)

Frequently asked questions

What is CVE-2025-64340?: CVE-2025-64340 is a medium-severity vulnerability in Jlowin Fastmcp, classified under OS Command Injection. CVSS score: 6.7/10. Published 2026-04-03.
How severe is CVE-2025-64340?: Medium severity. CVSS v3 base score is 6.7 out of 10.