SFTP Large File Transfer Exfiltration

Darshan Thummar@Mighty

•updated Jun 10, 2026•0•0•1

This rule detects potential Secure File Transfer Protocol (SFTP) large file exfiltration attempts. It triggers an alert when a TCP connection on port 22 (SFTP) from the home network to any destination transfers a large amount of data (greater than 65000 bytes) to the server. A threshold of 20 such transfers within 60 seconds from the same source IP is set to reduce false positives. The rule specifically looks for the SFTP protocol magic bytes '|00 00 00|' within the first 4 bytes of the payload.