FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name

Exploitation

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

CVSS 4.0

5.4 · CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2025-62801: 0.23% estimated exploitation activity in the next 30 days; percentile 13.54 (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.

Summary A command-injection vulnerability lets any attacker who can influence the servername field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor Details 1. generatecursordeeplink(servername, …) embeds servername verbatim in a cursor://…?name= query string. 2. opendeeplink() is invoked with shell=True only on Windows. That calls cmd.exe /c start <deeplink. 3. Any cmd metacharacter inside servername (&, |, , ^, …) escapes the start command and spawns an attacker-chosen process. PoC server.py then run in the terminal: fastmcp install cursor server.py Impact OS Command / Shell Injection (CWE-78) Every Windows host that runs fastmcp install cursor is at risk. Developers on their local workstations, CI/CD agents and corporate build machines alike.

Published by the source

29 Oct 2025, 15:39 UTC

Last modified by the source

7 Jul 2026, 17:56 UTC

Source last checked

26 Oct 2026, 13:35 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-rj5c-58rq-j5g5

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-rj5c-58rq-j5g5

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# Patch Next advisory brief: CVE-2025-62801

Advisory: FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name
IDs: CVE-2025-62801, GHSA-rj5c-58rq-j5g5
Record: https://patchnext.com/advisories/cve-2025-62801 (revision 3, source checked 26 Oct 2026, 13:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fastmcp 2.13.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI fastmcp: affected < 2.13.0; fixed in 2.13.0

## 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-rj5c-58rq-j5g5 (OSV record GHSA-rj5c-58rq-j5g5 lists affected ranges: PyPI fastmcp >=0 <2.13.0 (fixed))
- Verified: https://github.com/advisories/GHSA-rj5c-58rq-j5g5 (GitHub-reviewed advisory GHSA-rj5c-58rq-j5g5 lists affected ranges: PyPI fastmcp >=0 <2.13.0)

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