ScanSSH: Scanning the Internet for SSH Servers

SSH is a widely used application that provides secure remote login. It uses strong cryptography to provide authentication and confidentiality. The IETF SecSH working group is developing SSH v2, an improved SSH protocol that fixes cryptographic and design flaws in the SSH v1 protocol. SSH v2 compatible server software is widespread. Recently discovered security flaws make it critically important to find vulnerable SSH servers and update them. In this paper, we describe a method to determine with good precision how many servers supporting the various protocol versions have been deployed on the net. We describe the design and implementation of ScanSSH, a scanner that probes SSH servers for their software version, and discuss the results of scanning the Internet and our local networks for several months.