VM SSH Keys

The One-Time SSH Password (OTP) SSH secrets engine type allows a Vault server to issue a One-Time Password every time a client wants to SSH into a remote host using a helper command on the remote host to perform verification.

An authenticated client requests credentials from the Vault server and, if authorized, is issued an OTP. When the client establishes an SSH connection to the desired remote host, the OTP used during SSH authentication is received by the Vault helper, which then validates the OTP with the Vault server. The Vault server then deletes this OTP, ensuring that it is only used once.

Since the Vault server is contacted during SSH connection establishment, every login attempt and the correlating Vault lease information is logged to the audit secrets engine.

See Vault-SSH-Helper for details on the helper.

This page will show a quick start for this secrets engine. For detailed documentation on every path, use vault path-help after mounting the secrets engine.

Drawbacks

The main concern with the OTP secrets engine type is the remote host's connection to Vault; if compromised, an attacker could spoof the Vault server returning a successful request. This risk can be mitigated by using TLS for the connection to Vault and checking certificate validity; future enhancements to this secrets engine may allow for extra security on top of what TLS provides.

Mount the secrets engine

CLIUI

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$ vault secrets enable ssh
Successfully mounted 'ssh' at 'ssh'!

Go to the Secrets engine tab, click Enable new engine + , then select SSH to enable a new ssh engine.

Create a role

Create a role with the key_type parameter set to otp. All of the machines represented by the role's CIDR list should have helper properly installed and configured.

CLIUI

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$ vault write ssh/roles/otp_key_role \
    key_type=otp \
    default_user=username \
    cidr_list=x.x.x.x/y,m.m.m.m/n
Success! Data written to: ssh/roles/otp_key_role

Create a credential

Create an OTP credential for an IP of the remote host that belongs to otp_key_role.

CLIUI

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$ vault write ssh/creds/otp_key_role ip=x.x.x.x
Key             Value
lease_id        ssh/creds/otp_key_role/73bbf513-9606-4bec-816c-5a2f009765a5
lease_duration  600
lease_renewable false
port            22
username        username
ip              x.x.x.x
key             2f7e25a2-24c9-4b7b-0d35-27d5e5203a5c
key_type        otp

1. Click on the role.

1. Fill in the user name and IP address to generate SSH credentials.

Establish an SSH session

$ ssh username@x.x.x.x
Password: <Enter OTP>
username@x.x.x.x:~$

Automate it!

A single CLI command can be used to create a new OTP and invoke SSH with the correct parameters to connect to the host.

$ vault ssh -role otp_key_role -mode otp username@x.x.x.x
OTP for the session is `b4d47e1b-4879-5f4e-ce5c-7988d7986f37`
[Note: Install `sshpass` to automate typing in OTP]
Password: <Enter OTP>

The OTP will be entered automatically using sshpass if it is installed.

$ vault ssh -role otp_key_role -mode otp -strict-host-key-checking=no username@x.x.x.x
username@<IP of remote host>:~$

Note: sshpass cannot handle host key checking. Host key checking can be disabled by setting -strict-host-key-checking=no.