excel-mcp-server

Least-privilege permissions

• Restrict file storage location: Configure the server to save Excel files only to a dedicated folder (e.g., /safe-excel-files), not your entire computer or cloud storage. Prevent it from accessing or overwriting other directories.
• Use read-only accounts when possible: If the AI agent only needs to read existing data to create reports, set its account permissions to read-only rather than full edit access.
• Limit cloud storage connections: If connecting to OneDrive or Google Drive, use a dedicated app-specific password or token with minimal permissions—never share your main account credentials.
• Disable macro execution: Configure Excel to never auto-run macros from files created by this server, even if they appear legitimate.

Network isolation

• Run on a separate network segment: If possible, run the excel-mcp-server on an isolated machine or virtual environment, not your main work computer.
• Disable internet access: The server should not need to contact external websites or services; block outbound internet connections unless absolutely required.
• Use a firewall or VPN: Only allow authorized applications (Claude, Cursor, etc.) to communicate with the server; block unexpected connection attempts.
• Encrypt data in transit: If files must be transferred over a network, use encrypted channels (HTTPS, VPN, or secure file transfer protocols).

Monitoring

• Log all file creation and edits: Enable detailed logging to track when Excel files are created, who requested them, and what was modified—store logs in a tamper-proof location.
• Set up alerts for unusual activity: Create alerts if the server tries to access files outside its designated folder or creates unusually large files (potential data exfiltration).
• Review generated files before sharing: Manually inspect Excel files for unexpected formulas, hidden data, or sensitive information before sending to others.
• Track dependency updates: Regularly check for security patches to the server and its underlying libraries; subscribe to security advisories or use automated patch management tools.

Red flags to watch for

• Formulas that look suspicious: If Excel files contain formulas starting with =cmd, =powershell, or references to external websites, do not open them—these may be malicious.
• Files saved to unexpected locations: If Excel files appear in folders you didn't authorize, or if file sizes are unusually large, investigate before opening.
• Slow performance or crashes: Sudden freezing or repeated errors may indicate a denial-of-service attack embedded in a formula.
• AI responses including credentials: If the AI agent ever suggests adding passwords, API keys, or personal information directly into spreadsheets, reject this and report it—sensitive data should never be embedded in files.