If you’re an enterprise IT administrator, chances are you’ve been asked to investigate unknown or rogue SSH keys on your network. This can be daunting, given the potential for hundreds or even thousands of keys floating around. But don’t worry—we’re here to help. This blog post will walk you through a few best practices for dealing with unknown or rogue SSH keys and how you can remedy them with an SSH key manager.

What Are Rogue SSH keys?

First, let’s start with a definition. Unknown or rogue SSH keys are unlicensed, unauthorized keys that have been added to your server without your knowledge or consent. These keys can come from various sources, including employees who use them for work purposes, contractors who have access to your servers, and even malicious actors who may have gained access to your network through other means. 

Whatever the source, it’s essential to find and remove these keys as soon as possible. Not only do they pose a security risk, but they can also lead to compliance issues if you’re subject to regulations like PCI DSS or HIPAA. So how can you find and remove unknown or rogue SSH keys? Read on to find out.

How to Find Unknown or Rogue SSH Keys

The first step in dealing with unknown or rogue SSH keys is finding them. This can be tricky, depending on the size and complexity of your network. However, there are a few tools and techniques that can help:

Use key fingerprinting

When an SSH key is generated, it is assigned a unique fingerprint. This fingerprint can be used to identify the key and its corresponding owner. Use a tool like ssh-keygen to create fingerprints for all of the keys on your server, then compare those fingerprints against a database of known keys. Any fingerprints that don’t match up could belong to unknown or rogue keys.

Scan logs

Look through your server’s log files for any mention of SSH activity. If you see any suspicious activity—for example, login attempts from unrecognized IP addresses—there’s a good chance that someone is trying to access your server with an unknown or rogue key. 

How To Remove Rogue Keys

Once you’ve identified some potential unknown or rogue keys, it’s time to remove them from your system. Here are a few tips for doing so:

Modify your firewall rules

If you know the IP addresses associated with the unknown or rogue keys, you can block those addresses from accessing your server using firewall rules. This is a quick and easy way to mitigate the risk posed by those keys without having to delete them outright. Just be sure to add the new firewall rules before removing the old ones; otherwise, you could create an opening that malicious actors could exploit.

Revoke existing user accounts

Another option is to revoke the user accounts associated with the unknown or rogue SSH keys. This will prevent anyone from using those keys to gain access to your server in the future. Be sure to take this step carefully; if you accidentally revoke a legitimate user account, it could cause significant problems for your business. 

Delete the offending keys

Finally, if you’re sure that the keys in question are indeed unknown or rogue, you can delete them from your system entirely. This is a more extreme measure, but it may be necessary if the keys are used maliciously. As always, back up your data before taking this step.

SSH Key Management

The best way to deal with unknown or rogue SSH keys is to prevent them from being added to your system in the first place. This can be done with a tool known as an SSH key manager.

An SSH key manager is a software application that centrally stores and manages SSH keys. It can generate new keys, revoke existing ones, and assign permissions to specific keys. This allows you to tightly control who has access to your servers and what they can do once logged in.

A good SSH key manager will also include features like auditing and event logging, which can be invaluable for tracking unknown or rogue keys. 

Picking the Right SSH Key Manager

There are many SSH key managers on the market, so how do you know which one is right for your business? Here are a few factors to consider:

Ease of use

The SSH key manager should be easy for your staff to use. It should have a user-friendly interface and well-documented instructions.

Compatibility

Ensure the SSH key manager you choose is compatible with your operating system. 

Security

Above all, the SSH key manager should be secure. It should encrypt keys and offer other features like two-factor authentication to keep your data safe.

Pricing

Don’t overspend on an SSH key manager; there are plenty of affordable options on the market. 

The Bottom Line

Unknown or rogue SSH keys can pose a severe security risk to your business. But by taking simple precautions—like using an SSH key manager—you can help keep your data safe.