CVE-2025-64340: CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') in jlowin fastmcp
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.
AI Analysis
Technical Summary
The vulnerability in jlowin fastmcp occurs because server names with shell metacharacters (such as &) are not properly neutralized when passed to the 'fastmcp install claude-code' or 'fastmcp install gemini-cli' commands on Windows. Although subprocess.run() is used with a list argument, the Windows command-line environment executes .cmd wrappers through cmd.exe, which interprets metacharacters in the flattened command string, enabling OS command injection. This issue was fixed in version 3.2.0 of fastmcp.
Potential Impact
Successful exploitation allows an attacker with limited privileges and user interaction to execute arbitrary commands on the Windows system where fastmcp is run. The impact includes full confidentiality, integrity, and availability compromise of the affected system as indicated by the CVSS vector (C:H/I:H/A:H). There are no known exploits in the wild at this time.
Mitigation Recommendations
Upgrade fastmcp to version 3.2.0 or later, where this vulnerability has been patched. Since the vendor advisory confirms the fix in version 3.2.0, applying this official update is the recommended remediation. Patch status is confirmed by the vendor advisory content.
CVE-2025-64340: CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') in jlowin fastmcp
Description
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.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in jlowin fastmcp occurs because server names with shell metacharacters (such as &) are not properly neutralized when passed to the 'fastmcp install claude-code' or 'fastmcp install gemini-cli' commands on Windows. Although subprocess.run() is used with a list argument, the Windows command-line environment executes .cmd wrappers through cmd.exe, which interprets metacharacters in the flattened command string, enabling OS command injection. This issue was fixed in version 3.2.0 of fastmcp.
Potential Impact
Successful exploitation allows an attacker with limited privileges and user interaction to execute arbitrary commands on the Windows system where fastmcp is run. The impact includes full confidentiality, integrity, and availability compromise of the affected system as indicated by the CVSS vector (C:H/I:H/A:H). There are no known exploits in the wild at this time.
Mitigation Recommendations
Upgrade fastmcp to version 3.2.0 or later, where this vulnerability has been patched. Since the vendor advisory confirms the fix in version 3.2.0, applying this official update is the recommended remediation. Patch status is confirmed by the vendor advisory content.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2025-10-30T17:40:52.030Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69cfdd290a160ebd923d52bd
Added to database: 4/3/2026, 3:30:49 PM
Last enriched: 4/3/2026, 3:45:53 PM
Last updated: 4/4/2026, 5:44:31 AM
Views: 8
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.