How to configure SSH Keys for Nessus

IRJ

Enjoy

Create Scan User and Scan Group

sudo useradd -m scan_user
sudo groupadd scan
sudo usermod -aG scan scan_user

Create .ssh directory and set permissions

sudo mkdir /home/scan_user/.ssh
sudo chown -R scan_user:scan_user /home/scan_user

Generate key and set permissions


sudo -u scan_user ssh-keygen -f /home/scan_user/.ssh/id_rsa -t rsa -N ''
sudo -u scan_user mv /home/scan_user/.ssh/id_rsa.pub /home/scan_user/.ssh/authorized_keys
sudo -u scan_user chmod 0600 /home/scan_user/.ssh/authorized_keys
sudo -u scan_user chmod 0700 /home/scan_user/.ssh

Enable Public Key Authentication

sudo echo '' >> /etc/ssh/sshd_config
sudo echo '' >> /etc/ssh/sshd_config
sudo echo '#***********************************************************' >> /etc/ssh/sshd_config
sudo echo '# Enable RSA Key Authentication ' >> /etc/ssh/sshd_config
sudo echo '#***********************************************************' >> /etc/ssh/sshd_config
sudo echo 'PubkeyAuthentication yes' >> /etc/ssh/sshd_config
sudo echo 'RSAAuthentication yes' >> /etc/ssh/sshd_config

Set minimum permissions for scanning

sudo echo '' >> /etc/ssh/sshd_config
sudo echo '' >> /etc/ssh/sshd_config
sudo echo '#***********************************************************' >> /etc/sudoers
sudo echo '# Set minimum permissions for scanning ' >> /etc/sudoers
sudo echo '#***********************************************************' >> /etc/sudoers
sudo echo '%scan    ALL= NOPASSWD:/usr/sbin/dmidecode, /bin/netstat, /bin/uname' >> /etc/sudoers

Restart SSH

sudo systemctl restart sshd

Copy key file to your PC for upload to Nessus
Commented out so you can run manually.

# sudo scp /home/scan_user/.ssh/id_rsa remoteusername@remoteserver:servername_scan_key

Test Logging in via SSH Key from your box.
Commented out so you can run manually.

# ssh -i servername_scan_key scan_user@server

IRJ

All cleaned up

IRJ

Updated for 100% automation. Tested on Ubuntu 18.04 and Ubuntu 16.04

travisdh1

Thanks for posting this. I know how interesting their instructions are thanks to your adventures yesterday.

IRJ

@travisdh1 said in How to configure SSH Keys for Nessus:

Thanks for posting this. I know how interesting their instructions are thanks to your adventures yesterday.

You think this would be super important to them. I guess everyone just uses password auth with sudo access :man_shrugging:

Or maybe they just use windows :man_facepalming:

DustinB3403

@IRJ said in How to configure SSH Keys for Nessus:

Or maybe they just use windows

Those licenses aren't that expensive compared to the 15 seconds it takes to setup key access, right?

IRJ

@DustinB3403 said in How to configure SSH Keys for Nessus:

@IRJ said in How to configure SSH Keys for Nessus:

Or maybe they just use windows

Those licenses aren't that expensive compared to the 15 seconds it takes to setup key access, right?

Sure, but it took me half a day with terrible documentation.

I can understand some kb articles that are outdated/broken, but you think account setup would be an extremely important article that is maintained and tested at least quarterly. Whoever wrote that article, did not only have incorrect information, but they seemed to have never made a blog post before.

Sometimes explanations came before or after the listed command, and some things had no explanations at all. It wasnt even consistent throughout the article.

DustinB3403

@IRJ said in How to configure SSH Keys for Nessus:

Sure, but it took me half a day with terrible documentation.

But you also didn't follow the KISS method and blindly followed that bad documentation. Rather than stepping back and saying "there is no f'ing way it's this difficult on linux"

DustinB3403

Isn't this step redundant?

sudo mkdir /home/scan_user/.ssh
sudo chown -R scan_user:scan_user /home/scan_user

As ssh-keygen will create these directories and set the ownership?

IRJ

@DustinB3403 said in How to configure SSH Keys for Nessus:

Isn't this step redundant?
sudo mkdir /home/scan_user/.ssh
sudo chown -R scan_user:scan_user /home/scan_user
As ssh-keygen will create these directories and set the ownership?

It could be extra steps, but we are not charged per command issued in the terminal

Especially since it was scripted.

IRJ

@DustinB3403 said in How to configure SSH Keys for Nessus:

Isn't this step redundant?
sudo mkdir /home/scan_user/.ssh

I think that one is needed, but you could do it like this without elevating priveleges.

sudo -u scan_user mkdir /home/scan_user/.ssh

JaredBusch

@DustinB3403 said in How to configure SSH Keys for Nessus:

Isn't this step redundant?
sudo mkdir /home/scan_user/.ssh
sudo chown -R scan_user:scan_user /home/scan_user
As ssh-keygen will create these directories and set the ownership?

It certainly does on Fedora.