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 install gemini-cli. These install paths use subprocess.run() with a list argument, but on Windows the target CLIs often resolve to .cmd wrappers that are executed through cmd.exe, which interprets metacharacters in the flattened command string. This issue has been patched in version 3.2.0.
Vulnerability class: Command Injection (OS Command Injection)
EPSS: 0.007 (50.7th 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)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Patch, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC, Issue Tracking)
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.