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For #4, wouldn't the only change when someone leaves the organization be to remove their key from authorized_keys for the shared account? Why would anyone else have to be updated?

It's a basic principle of security. Each account represents one person so that you have a full audit of who did what by watching the activity of a given user account. If everything is run as "devops" user for example, you have no idea who actually performed a given task. Was it Bill, or was it an automated job? PCI-DSS requirements also affect your model for user accounts (hint: shared users are often not compliant).

From the perspective of a sysadmin, this article has a lot of issues and it's inadvisable to follow its recommendations. Who doesn't use a hardware firewall? Who exposes ssh to the internet (requiring fail2ban) when a VPN server is much more secure and easier to use? Setting up an LDAP server is really easy and costs nothing. There's no excuse for shared accounts.

Why do you say a VPN server is more secure? Which one?

I, for one, trust ssh more than any other software wrt security, especially with password login disabled. Disclaimer: I am not a security expert.

I, also, trust SSH more than any other software. But it is still worth adding an additional layer of security in front of SSH to help protect from exploits.

Let's say that, hypothetically, a 0-day exploit was discovered in SSH which allowed remote code execution. A script kiddie begins trawling the internet for publicly accessible SSH servers to attack.

Your servers allow SSH from anywhere on the internet, and are eventually discovered and exploited. Mine, which will only allow SSH connections from my VPN bastion host, are effectively invisible to the attacker and will not get exploited (by this particular script kiddie, at least).

Adding a VPN server in front of SSH won't protect you from an APT, but it will protect you from 99% of the random, automated attacks that take place.

Your outermost server is the one where you should be most worried about having vulnerabilities - if you have a VPN as the outer layer that means the VPN server must be exposed to the public internet, and anyone who compromises it is in a pretty good position. And I'd rate the odds of a 0-day being found at higher for most VPN software than for SSH.

anyone who compromises [the VPN server] is in a pretty good position.

Sure. But without a VPN, anyone who compromises even one of your other hosts is in the same position. It's a lot easier to audit a single-purpose VPN server for possible security issues than it is to audit all the application code running on the rest of your production systems.

And I'd rate the odds of a 0-day being found at higher for most VPN software than for SSH.

I wouldn't. And even if you're right, getting a VPN login still doesn't get you anywhere. You still have to be able to ssh to the rest of the hosts. That's why we do security in layers.

Ok, just in case it wasn't clear: I am asking about the advantages of having a VPN server as a bastion host instead of another SSH server.

You would ssh to the bastion host, and from there to internal hosts.

With the appropriate ssh config at the client end, the tunneling through the bastion can be scripted away (using the ProxyCommand directive and RSA keys).

Routing transparency. Sure, you can script a bunch of tunnels, but it's nice to handle routing at a lower layer. Having worked with both setups, I vastly prefer the VPN solution for ease of setup, use, and maintenance.

Also, different attack surfaces. Two layers of the same security measure (ssh) is, all else equal, not quite as good as two layers involving two different measures (VPN, ssh).

Same question - which open source VPN solution would you recommend?

I liked the idea of adding VPN layer to SSH, so would like to get as much advice as possible :-)

I have experience with many open source VPN servers. The purpose is a bit different -- we provide a VPN service to home users to encrypt their internet traffic. But the same problems should apply.

OpenVPN is the most compatible with a variety of clients. OpenVPN runs in userspace, so the clients for each OS and mobile platform interoperate well. The downside is, it does require a client program to be installed and configured. It's considered very secure, using SSL. Since it's userspace, moving large amounts of traffic means more context switching and higher cpu usage. Despite that, I've found it to be faster and more stable than the alternatives.

L2TP/IPSec is built in to most clients -- Windows, OS X, mobile. But every implementation is different and it's hard to configure a server to work with all of them. There are also more moving parts -- an IPSec server (openswan, strongswan, or racoon), and L2TP server (openl2tpd, xl2tpd) and a PPP server (pppd). IPSec seems to be a secure protocol but it's very complicated. I tend to distrust complicated security.

Pure IPSec has many of the problems of L2TP/IPSec with the added problem of difficult to configure in Windows and OS X.

PPTP is not performant or very secure. Other than the fact that almost every client supports it, I see no reason to use it for a new VPN.

I've had success with OpenVPN. I don't know that I'd specifically recommend it over other options, as I don't have much experience with anything else.

Yes, I agree, I was just giving an example of how an additional layer can help protect against automated attacks, even for highly-secure services like SSH.

I also agree that SSH is less likely to have flaws than most VPN software. But on a properly configured bastion host, by-passing the VPN would just put you in a position where you can attack SSH. You would still need to by-pass SSH to access production servers.

Which open source VPN solution would you recommend?

> and anyone who compromises it is in a pretty good position.

You are assuming the VPN host is trusted any more than most people trusts random servers on the internet.

I am, just from my experience in real-life companies. It takes an awful lot of discipline to treat servers as if they were exposed to the public internet when you know full well that they're not.

This is just faulty logic.

openssh is one of the most secure projects. It's developed by the security obsessed (and I mean it in a kind way) folks at OpenBSD.

I, for one, am ready to place for more trust in openssh than in any VPN daemon. The most commonly used ones are propitiatory.

What if there is a 0-day vuln (not exploit) for these VPN daemons? That far more likely. "Securing" ssh with a VPN is just one step beyond of security by obscurity.

If you are afraid of script-kiddies and scanners, let your sshd listen on a non-standard port.

Port scanners do generally scan non-standard ports too, you know...

I don't think that exposing SSH to the internet is that bad, but your argument is not sound - requiring a VPN does add security, because if there happened to be a vulnerability in it that allowed access, all it would do is expose SSH on the machines (I'm assuming you have proper firewalls set up), which you are advocating making public in the first place.

Saying it adds no security is false, because you'd require an unpatched vulnerability both in your VPN server and in the SSH server simultaneously. A zero-day in one is possible, but in both at the same time is far, far less likely.

> "Securing" ssh with a VPN is just one step beyond of security by obscurity.

You're not securing ssh with a vpn. You're adding another layer. ssh is still secured by all of ssh's existing protection.

ssh behind a vpn requires that someone both compromise the vpn _and_ compromise the ssh service to gain that access that, without a vpn, would require them to only compromise the ssh service.

Your servers allow SSH from anywhere on the internet, and are eventually discovered and exploited. Mine, which will only allow SSH connections from my VPN bastion host, are effectively invisible to the attacker and will not get exploited

So, just to see if I'm reading you right: you're using a VPN in the place of an SSH jump box, not making a judgement about the fitness or trust placed in your VPNd over your SSHd.

When someone advocates using a VPN, that doesn't mean not using SSH too. VPN + firewall just restricts who has the potential to try to SSH to you, and provides additional protection and central access control/management.

Agreed, anyone who has touched PCI DSS would agree you need to associate access with a human user. This would not work. If you look at the security logs it won't differentiate between which keys were used for that generic account.

It's a good idea to use fail2ban even if you use VPN.

If they have had access to a shared account, how much work are you willing to put in to verify that there's nothing in that shared account that will get executed by another user later that will quietly reinstate a key?

A reason to have separate accounts is that not only do you terminate access, you also have an easier time ensuring that less of what that person had access to could have been compromised. (This of course goes right out the window if said person has sudo/su access, in which case you have a much harder time, but even then giving them individual accounts means your opportunity to audit becomes so much greater)

After all, it's not the honest guy who'll never try to log in again you're primarily trying to protect against (in fact: for the honest people, a good security policy protects them by making them less likely to become potential suspects if/when something happens - it's in your own interest when you leave an organisation to ensure you get locked out), but the guy who might decide to try to do something later, or who might even be thinking about doing something before they leave.

But if you give people any access to any system surely this is a concern. As a software dev, maybe I've inserted something into one of the build scripts that quietly re-opens my backdoor to the source control server...

I haven't, but if you assume actually malicious users you're probably going to end up with something so locked down it's useless. Aren't you?

It's commonly stated that 9 out of 10 security threats come from employees or other insiders. You should assume malicious employees. Sooner or later you will hire the wrong person.

Now, you must also have a functioning system, and so you may take risks by leaving things more open than you would like if you don't have the resources to thoroughly lock everything down.

But wherever locking things down further costs you very little, you should take the opportunity. And elsewhere you should asses what level of protection you can afford. Ultimately it is a cost-benefit analysis. Many risks are not worth spending money protecting against. Others are vital.

But even disregarding malicious users: Individual user accounts is not just a protection against malicious users, but against careless users. When someone sets a password that gets guessed, you want to be in a position where exploiting that persons credentials is as hard as possible, and tracking down actions taken via the account is as easy as possible.

And yes, you could insert something into a build script. But if the build script is committed, and the commit was pushed from a named, individual account, you're now at the risk of going to jail. Creating deterrents is often a sufficient risk mitigation strategy to be acceptable.

Quite the contrary: You're probably going to end up with documented procedures for deploying software that are simplified, follow existing standards/best practices, and don't rely on complex stone soup build/init scripts concocted by inexperienced developers (and I've seen some doozies).

A developer is more likely to create better and more easily maintainable software if the target audience is assumed to be an ordinary user with no special system privileges. In my experience, when a developer has root and assumes everyone else does, deployment becomes a nightmare.

Not quite sure I understand what you're saying here, I'm not talking about the software being produced, but the systems used to produce it.

What I was trying to say was that there's not really any way for you (server admin guy) to know if I (software dev guy) have inserted something malicious into a script that all the other software folks run constantly (software build system, NOT server build/init script, NOT deployment script).

This is not about the end-user's privileges, or server set up, just how in a team-base software dev environment you're probably going to have to have a measure of trust for your employees.

I see, but I think the same principle applies, even in this narrow case. As a server admin guy or fellow software dev guy, I have to trust that any code you've written has been properly reviewed before checking it into a repository that I pull from. Fortunately, version control tools make this trivial, but you're right, the policy and infrastructure supporting it has to be in place, otherwise you're depending only on voluntary peer review.

Note that as an attacker, there's a high risk of exposure and identification in the scenario you describe, and that's a good thing. A well secured system shouldn't merely prevent attacks, it should also protect innocent users from suspicion (another reason why shared accounts are discouraged).

But they still would know the 'deploy' password needed for sudo access. And while you could be relatively sure that they couldn't get access, you still couldn't be completely sure since they did have sudo access to begin with. So, the best thing would be to change the shared password. That could be avoided with non-shared accounts.

Are you insinuating that the user could have used sudo access to install a backdoor of some sort? If so, changing the password won't stop them either. Am I missing something?

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