FastMCP has a Command Injection vulnerability - Gemini CLI

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.7 · CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

EPSS

• CVE-2025-64340: 0.75% estimated exploitation activity in the next 30 days; percentile 54.93 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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. PoC: On Windows, this opens Calculator via the &calc in the server name. Impact: Arbitrary command execution with the privileges of the user running fastmcp install. Affects Windows hosts where the target CLI (one of claude, gemini) is installed as a .cmd wrapper. Does not affect macOS/Linux, and does not affect config-file-based install targets (cursor, goose, mcp-json). Patched in #3522 by validating server names to reject shell metacharacters.

Published by the source

31 Mar 2026, 22:24 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:40 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m8x7-r2rg-vh5g

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-m8x7-r2rg-vh5g

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# Patch Next advisory brief: CVE-2025-64340

Advisory: FastMCP has a Command Injection vulnerability - Gemini CLI
IDs: CVE-2025-64340, GHSA-m8x7-r2rg-vh5g
Record: https://patchnext.com/advisories/cve-2025-64340 (revision 2, source checked 26 Oct 2026, 13:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fastmcp 3.2.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI fastmcp: affected < 3.2.0; fixed in 3.2.0

## Suggested inspection (read-only)
- `python -m pip show fastmcp`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fastmcp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-m8x7-r2rg-vh5g (OSV record GHSA-m8x7-r2rg-vh5g lists affected ranges: PyPI fastmcp >=0 <3.2.0 (fixed))
- Verified: https://github.com/advisories/GHSA-m8x7-r2rg-vh5g (GitHub-reviewed advisory GHSA-m8x7-r2rg-vh5g lists affected ranges: PyPI fastmcp >=0 <3.2.0)

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