If your Python application offers CSV export of user-generated data, that user-generated data might contain malicious payloads that might trigger vulnerabilities in the spreadsheet software of the user that downloads the file (i.e. MS Excel or LibreOffice).

This library tries to mitigate that by prepending all cells starting with @, +, -, =, | or % with an apostrophe ' and additionally replacing all | characters in these cells with \|. This will of course change the resulting CSV files, but Excel will not display the ' character to the user.

Tested with Python 3.8 to 3.10.

This library acts as a drop-in replacement for the standard library's csv module. You can use it by just replacing import csv with from defusedcsv import csv in your code.

• CSV Injection Software Attack | OWASP Foundation
• Comma Separated Vulnerabilities | Context Information Security
• CSV Injection Mitigations & Dangers | ZeroSec - Adventures In Information Security

The code in this repository is published under the terms of the Apache License. See the LICENSE file for the complete license text.

This project is maintained by Raphael Michel <[email protected]>. See the AUTHORS file for a list of all the awesome folks who contributed to this project.