T1098.004 - SSH Authorized Keys
Description from ATT&CK (opens in a new tab)
Adversaries may modify the SSH
authorized_keys
file to maintain persistence on a victim host. Linux distributions, macOS, and ESXi hypervisors commonly use key-based authentication to secure the authentication process of SSH sessions for remote management. Theauthorized_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
(or, on ESXi,/etc/ssh/keys-<username>/authorized_keys
).(Citation: SSH Authorized Keys) Users may edit the system’s SSH config file to modify the directivesPubkeyAuthentication
andRSAAuthentication
to the valueyes
to ensure public key and RSA authentication are enabled, as well as modify the directivePermitRootLogin
to the valueyes
to enable root authentication via SSH.(Citation: Broadcom ESXi SSH) 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. In cloud environments, adversaries may be able to modify the SSH authorized_keys file of a particular virtual machine via the command line interface or rest API. For example, by using the Google Cloud CLI’s “add-metadata” command an adversary may add SSH keys to a user account.(Citation: Google Cloud Add Metadata)(Citation: Google Cloud Privilege Escalation) Similarly, in Azure, an adversary may update the authorized_keys file of a virtual machine via a PATCH request to the API.(Citation: Azure Update Virtual Machines) 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) It may also lead to privilege escalation where the virtual machine or instance has distinct permissions from the requesting user.Where authorized_keys files are modified via cloud APIs or command line interfaces, an adversary may achieve privilege escalation on the target virtual machine if they add a key to a higher-privileged user.
SSH keys can also be added to accounts on network devices, such as with the
ip ssh pubkey-chain
Network Device CLI (opens in a new tab) command.(Citation: cisco_ip_ssh_pubkey_ch_cmd)
Atomic Tests
Atomic Test #1 - Modify SSH Authorized Keys
Modify contents of
Supported Platforms: Linux, macOS
auto_generated_guid: 342cc723-127c-4d3a-8292-9c0c6b4ecadc
Attack Commands: Run with sh
!
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