Exploring SSH Key Rotation with Thycotic Secret Server

Everyone knows and should be aware of the huge security issues there are surrounding the Windows administrator account, and there is a ton of guidance on how to properly secure that particular account, how to avoid password compromises, and how to use alternatives. But there seems to be much less intense focus on securing privileged accounts on Linux, and especially the idea that SSH keys are much like passwords in their absolute need to be protected at all costs.

SSH keys start out the security race ahead of passwords because they require two parts that do not exist in the same location all the time—a private key, which is often protected by a passphrase, is compared with a public key, and cryptographic analysis is carried out to determine if a user is authenticated to a system. This avoids the wholesale compromise of credentials just by gaining access to a system, since all that system would have is the public keys for authorized users. The other half of the puzzle, those users’ private keys, does not exist on the system anywhere.

Unfortunately, out of convenience or perhaps at the time, sheer necessity, the same private keys are re-used across multiple machines. This might be to make it easier for developers and testers to connect to a farm of Linux or Unix machines before they are moved collectively into production, or it may be that a single administrator is responsible for all of them and feels that he can properly secure that one single, well-formulated private key. It may even be an artifact of cloning a bunch of new virtual machines from an existing “template” image, or a relic of being able to easily automate a bunch of actions across a number of different machines using a single private key.

But of course, there is more to it than just one unique individual private key per user per machine. Those keys ought to be rotated and changed out, just like passwords should. This is for a variety of reasons: first, systems that contain private keys can be compromised, or the passphrases that protect the private keys can be compromised. Especially as news breaks today that the WPA2 wireless encryption technology has been broken and unprotected resources behind a vulnerable access point could be compromised, it is more important than ever to never fully trust a static key, password, phrase, or anything else, and make sure that secret is changed regularly.

The process of rotating keys is simple, but carrying it out is definitely not easy. Essentially it is a four-part process: you need to generate new keys, install that key into the authorized_keys file on all of your machines, test that new key, and then remove the stale key from that same authorized_keys file.

Brave folks use Ansible to take care of system administration tasks like these in an automated way, but then you need to spend time thinking about playbooks and plays and trying to make all of those pieces play together nicely. That all works well enough, and for the smallest deployments with the most limited of budgets it is a reasonable solution. But what about when the powers that be want proof your Linux or Unix endpoints are correctly protected this way? What if you need to easily control who can access those keys from an administrative staffing perspective? You need a stronger tool, and the folks at Thycotic have a proposition: why not use software designed from the start to automate the protection of our most sensitive privileged accounts and let it take care of the dirty work for you?

Thycotic Secret Server to the Rescue

Enter their Secret Server product and specifically the SSH Key Management function. This program will generate new keys and rotate them out either on demand or on a previously determined schedule, control via a role-based access control scheme and robust permissions which users have access to which keys, and provide a complete audit trail of which keys were sent where and when and who used them to access which systems on what date and time. Cobbling that together with Ansible would be a lot tougher and not nearly as seamless.

Thycotic asked me to spend some time evaluating this aspect of Secret Server and share my thoughts on the product.

My objective: get SSH key rotation going among 25 different Ubuntu virtual machines I have running in Amazon Web Services as part of another project. I installed a trial version of Secret Server on a Windows Server 2012 R2 box and added Microsoft SQL Server 2014 Express at the prompting of the installer. After completing the setup wizard, which was reasonably simple (although I did have to close and restart it due to an HTTPS binding issue which it automatically fixed), I went to the console and popped my license information in and enabled the Remote Password Changing settings. Then, I set out to create a new secret in Secret Server. Reading the Quick Start guide, I went with the Unix Account (SSH Key Rotation) template. On the template screen, I entered a friendly name for an account on one of those 25 machines as well as its username and password. I uploaded the private key file in .PEM format and entered its passphrase. I clicked the button and then watched for the Last Heartbeat field to say “Success” with an associated timestamp – that told me I was ready to go. I also liked I could just launch Putty and get signed in with one click – very convenient.

After that, I went to the Remote Password Changing tab and clicked Change Password Remotely. I generated a random password and then clicked Generate New SSH Key to get a new key. I also clicked the Generate button next to the Next Private Key Passphrase field to get a new protective passphrase. I clicked Change at the bottom and that was it. The key was rotated.

I went ahead and added a few of the other machines I was working with on that project and it all worked the same way as the previous one – add the secret, kick off the change, be done. It was a little work to get it set up but now I have a tool where with, what, three clicks? Four clicks? I can rotate keys all from a single point of management.

Pretty neat tool.

A Ransomware Removal Guide

An edited version of this article ran on the Netwrix blog on June 29, 2017. Credit: Netwrix

Ransomware is one of the biggest scourges we face as Internet citizens today. What happens when you have been struck by it? The most obvious option is to pay the ransom. If you did, you would not be alone: even large companies and non profits have had to pay up or at least negotiate a ransom payment. But should that be your first option? Hardly. Here are some tips about how to initially recover from a ransomware attack.

Have good backups

It just so happens that the best defense is a good offense and in this case, a good offense happens to also be the best defense after a ransomware attack infects your network: having good backups. This can come in a couple of forms:

  • Shadow copies. You may be familiar, if you are a Windows administrator, with the Volume Shadow Copy Service, a piece of software first introduced in Windows Server 2003 that takes snapshots of data on specifically configured volumes at predetermined points in time. This service informs the Previous Versions feature in Windows client, where if you do something stupid in a spreadsheet, for example, you can right-click the file on disk and choose to open a previous version made before your mistake. If you catch a ransomware infection early, chances are shadow copies are a good way to restore an unencrypted version of your files. If you are not using shadow copies, configure them today. Unfortunately, some variants of ransomware have caught on to this procedure and during their silent infection process, prior to encrypting files, they delete all shadow copies found on a disk.
  • Regular backups that you restore from tape or archive disk. You are taking regular backups of your storage system, right? And you are regularly testing those restores so that you are able to verify you backed up good files and can restore them intact? If not, then stop reading right now and go configure a backup scheme. If you are, then rest a little easier. The worst case for a ransomware infection is to wipe your machines and put data back on them from restored backups. Sure, it is an investment of time, but you absolutely do not need to pay any ransom, and you just might be seen as a hero.

See if a free decryptor is available

If you do find yourself on the other end of a ransomware attack that has completed, you have a couple of options that don’t involve paying the ransom.

As governments and security researchers continue to make progress against the ransomware threat, these parties have managed to break the encryption schemes used by some variants of ransomware. It is important to keep in mind that not every variant of ransomware has been “broken” by the good guys, so you should not rely solely on the promise that some of these encryption schemes have been foiled and rest on your laurels when it comes to building defenses against this type of attack.

But if you have already been victimized, then head over to The No More Ransom Project at https://www.nomoreransom.org and look for the variant you have been hit with. (This site is sponsored jointly by the European Cybercrime Center, Politie, Kaspersky Lab, and Intel Security. On the site, there are currently decryptor tools available for the following variants:

  • Crysus
  • Marsjoke/Polyglot
  • Wildfire
  • Chimera
  • Teslacrypt
  • Shade
  • Coinvault
  • Rannoh
  • Rakhni

These folks are working on breaking other variants as well, but of course breaking good encryption takes time, and the malware creators also have a perverse incentive to make their encryption stronger and even more unbreakable. It is an unfortunate dance, but for now, you might be able to save yourself with the decryptor tools on the site. A big red flashing warning here, though, to beware of tools from other places—they may actually be ransomware disguised as a prevention tool.

Use the File Server Resource Manager to catch bad actors

Even if you have been infected by ransomware, it is not too late to prevent further damage. You will likely have some encrypted files, but the sooner you stop the spread of the infection, the fewer files end up being held hostage, and the easier your cleanup task is. We have covered using a built in tool within Windows Server, called the File Server Resource Manager, on this blog before to catch ransomware attacks at they happen. Essentially you create a honeypot share with a dollar sign in front of the name to fool ransomware into starting with that particular share in its efforts to encrypt files. You let the group Authenticated Users have full control of this share so that any process that wants to write to that share can (although you do not publicize this share to users; this is only to catch things that should not be on your systems, not a drop box for other files). There is no legitimate use of the honeypot share, so when the File Server Resource Manager file screen notices write activity happening within that share, it can safely assume that someone has been infected, and it will cut off that user’s access to any share to stop the spread of the encryption attack in its tracks. There is a simple PowerShell script that can be fired by the File Server Resource Manager in order to accomplish this:

Get-SmbShare -Special $false | ForEach-Object { Block-SmbShareAccess -Name $_.Name -AccountName ‘[Source Io Owner]’ -Force }

 

Once permissions have been removed, the ransomware has no files it can access to encrypt, and it basically just stops. You then could clean the malware off, restore the files that were written to in that timeframe, and move on with your life.

For much more detail on this way to stop a pending attack, or an attack that is just beginning, check out Ransomware Protection Using FSRM and PowerShell [https://blog.netwrix.com/2016/04/11/ransomware-protection-using-fsrm-and-powershell/] on our blog.