T1098.004.md

T1098.004 - SSH Authorized Keys

Description from ATT&CK

Adversaries may modify the SSH authorized_keys file to maintain persistence on a victim host. Linux distributions and macOS commonly use key-based authentication to secure the authentication process of SSH sessions for remote management. The authorized_keys file in SSH specifies the SSH keys that can be used for logging into the user account for which the file is configured. This file is usually found in the user's home directory under <user-home>/.ssh/authorized_keys.(Citation: SSH Authorized Keys) Users may edit the system’s SSH config file to modify the directives PubkeyAuthentication and RSAAuthentication to the value “yes” to ensure public key and RSA authentication are enabled. The SSH config file is usually located under /etc/ssh/sshd_config.

Adversaries may modify SSH authorized_keys files directly with scripts or shell commands to add their own adversary-supplied public keys. This ensures that an adversary possessing the corresponding private key may log in as an existing user via SSH.(Citation: Venafi SSH Key Abuse) (Citation: Cybereason Linux Exim Worm)

Atomic Tests

• Atomic Test #1 - Modify SSH Authorized Keys

Atomic Test #1 - Modify SSH Authorized Keys

Modify contents of /.ssh/authorized_keys to maintain persistence on victim host. If the user is able to save the same contents in the authorized_keys file, it shows user can modify the file.

Supported Platforms: macOS, Linux

Attack Commands: Run with bash!

if [ -f ~/.ssh/authorized_keys ]; then ssh_authorized_keys=$(cat ~/.ssh/authorized_keys); echo $ssh_authorized_keys > ~/.ssh/authorized_keys; fi;

Cleanup Commands:

unset ssh_authorized_keys