CVE-2025-62801
📋 TL;DR
CVE-2025-62801 is a command injection vulnerability in FastMCP that allows attackers to execute arbitrary operating system commands on Windows hosts by manipulating the server_name field. This affects Windows systems running fastmcp install cursor with FastMCP versions before 2.13.0. Attackers who can influence the server_name parameter can achieve remote code execution.
💻 Affected Systems
- FastMCP
📦 What is this software?
Fastmcp by Jlowin
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining administrative privileges, data exfiltration, ransomware deployment, and persistent backdoor installation.
Likely Case
Unauthorized command execution leading to data theft, lateral movement within the network, and installation of malware or crypto-miners.
If Mitigated
Limited impact due to network segmentation, least privilege configurations, and proper input validation preventing successful exploitation.
🎯 Exploit Status
Exploitation requires ability to influence the server_name field, which typically requires some level of access or social engineering.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.13.0
Vendor Advisory: https://github.com/jlowin/fastmcp/security/advisories/GHSA-rj5c-58rq-j5g5
Restart Required: Yes
Instructions:
1. Stop all FastMCP services. 2. Update FastMCP to version 2.13.0 or later using 'pip install fastmcp>=2.13.0'. 3. Restart FastMCP services. 4. Verify the update with 'fastmcp --version'.
🔧 Temporary Workarounds
Input Validation for server_name
allImplement strict input validation and sanitization for the server_name field to prevent command injection.
# Implement server_name validation in your FastMCP application code
# Example: Validate server_name contains only alphanumeric characters and hyphens
import re
def validate_server_name(name):
return bool(re.match(r'^[a-zA-Z0-9\-]+$', name))
Network Segmentation
windowsIsolate FastMCP instances from critical systems and limit network access.
# Configure firewall rules to restrict FastMCP network access
# Example Windows firewall command:
netsh advfirewall firewall add rule name="Block FastMCP" dir=in action=block program="C:\path\to\fastmcp.exe" enable=yes
🧯 If You Can't Patch
- Implement strict input validation and sanitization for all user-controlled fields, particularly server_name.
- Run FastMCP with least privilege accounts and implement network segmentation to limit potential damage.
🔍 How to Verify
Check if Vulnerable:
Check FastMCP version with 'fastmcp --version'. If version is below 2.13.0 and running on Windows with 'fastmcp install cursor', the system is vulnerable.Check Version:
fastmcp --versionVerify Fix Applied:
Verify FastMCP version is 2.13.0 or higher with 'fastmcp --version'. Test server_name input with special characters to ensure they are properly sanitized.📡 Detection & Monitoring
Log Indicators:
- Unusual command execution patterns in Windows event logs
- FastMCP process spawning unexpected child processes
- Failed attempts to inject commands in server_name field
Network Indicators:
- Unexpected outbound connections from FastMCP hosts
- Command and control traffic patterns
SIEM Query:
source="windows_security" AND event_id=4688 AND (process_name="cmd.exe" OR process_name="powershell.exe") AND parent_process_name="fastmcp.exe"