CVE-2025-64340: FastMCP has a Command Injection vulnerability - Gemini CLI
Affects fastmcpSource GCVE Database
Not known to be exploited · CVSS 6.7 Medium : upgrade to 3.2.0 when convenient.
Data as of 30 Oct 2026, 07:30 UTC
- Patch
- Available – fixed in 3.2.0
CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 3 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
Upgrade fastmcp to 3.2.0.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Homebrewfastmcppkg:brew/fastmcpOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
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: ```python from fastmcp import FastMCP mcp = FastMCP(name="test&calc") @mcp.tool def roll_dice(n_dice: int) -> list[int]: """Roll `n_dice` 6-sided dice and return the results.""" return [random.randint(1, 6) for _ in range(n_dice)] ``` ``` fastmcp install claude-code server.py # or: fastmcp install gemini-cli server.py ``` 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.
References
- github.com/PrefectHQ/fastmcp/security/advisories/GHSA-m8x7-r2rg-vh5g (opens in a new tab)
- github.com/jlowin/fastmcp/security/advisories/GHSA-m8x7-r2rg-vh5g (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2025-64340 (opens in a new tab)
- github.com/PrefectHQ/fastmcp/pull/3522 (opens in a new tab)
- github.com/PrefectHQ/fastmcp (opens in a new tab)