How it was found

Dear GitLab bug bounty team,

Summary

GitLab allows users to export issues as a .csv file. By injecting a payload into an issue title an attacker could exfiltrate data or execute code on the target machine. For instance, by naming an issue =cmd|' /C calc'!A0 I am able to open up calc.exe on Windows.

Steps to reproduce

1. Create an issue with =cmd|' /C calc'!A0 as the title;
2. Export all issues (The file is sent as an email attachment);
3. Open the .csv file on a Windows machine.

Result: calc.exe pops up.

Fix

Prefix =, +, - and @ symbols with a ' in issues when exporting them to a .csv file.

If you require any further information, feel free to contact me.

Best regards, Ed