If another IP address shows up with the public key of a known host, the user logging on is alerted. This file captures IP address and host public key information to ensure authentication happens properly at the system level before a user logs on via SSH. Once an administrator begins a SSH session to a remote system for the first time, they’ll notice that an entry is added to the known_hosts file of the current user. That said, if an adversary gains access to the private key associated with this key-based authentication relationship, they can authenticate to a system via SSH without knowing any additional passwords. After changing a few lines in the SSH daemon configuration file, the service is hardened to prevent simple brute-force intrusion. To do this, administrators may use ssh-keygen to generate a key-pair before using ssh-copy-id to deploy the generated public key as appropriate to the authorized_keys file of a remote system’s user. To mitigate this, SSH sessions are often authenticated using public key cryptography. If administrators have chosen a non-complex password for well-known user accounts, brute-force attacks will likely succeed. Especially on the internet, attackers attempt to brute force access to systems via SSH. The usernames and passwords are the same ones used for logging on to a system at the keyboard, and it quickly becomes problematic when the SSH daemon’s port (22) is exposed on a network. When using SSH, administrators usually start out using the ssh command with a username and password combination. It’s a de facto standard of modern administration of Unix-like systems. SSH is versatile as a network protocol and can encapsulate other protocols to help secure them with encryption. The OpenSSH project also contains scp (Secure Copy) to replace an older unencrypted copy utility and sftp to replace older unencrypted uses of ftp. It’s best known for its association with the OpenSSH project and the ssh command that administrators use for text-based administration similar to Telnet. SSH is an encrypted network protocol that facilitates remote management of systems that are usually Unix-like. This time, I want to discuss a lesser publicized lateral movement technique: malicious use of Secure Shell (SSH) services. Scores of other blogs discuss Server Message Block (SMB) and Remote Desktop Protocol (RDP) lateral movement at great length. We’ve written a ton about this topic over the years, covering PsExec and other tools that enable adversaries to move laterally between systems. Lateral movement is a nearly ubiquitous attack tactic, as adversaries hardly ever gain initial access to the exact system that holds their objective.
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