Terminal Server without VPN for remote access 3


Before I get going, please comment on this. I am wanting more information, so please share.

I was wondering, though, why use a vpn to tunnel a terminal server connection? Isn’t terminal server encrypted already? Here’s a couple things that I *think* are important:

1. The vpn connection is no more secure than the terminal server. Why, if a trogan program runs on your remote client, what difference is it that you have a vpn to cover your terminal server? The attacker has access to the remote client, they now can get into your network with either system.
2. The vpn connection opens up a whole mess of insecurity if your remote client is compromised. (of course, it does with terminal server as well)
3. The data is never on the client if you use a terminal server, but with vpn, you open up your network. OUCH!
4. This is the one that really get’s me… with a vpn, if your remote client gets a nasty virus, your whole corporate network will probably now have it too once that vpn connection is opened. Not so with terminal server.
5. At least with terminal server, you can totally restrict apps and printing and such, so nothing is ever on the client, it only receives the screen shot of the server.
6. Brute forcing usernames and passwords are vulnerable on both.
7. If you were really worried about security… YOU WOULDNT RUN ANYTHING ON THE INTERNET! You wouldnt run IIS, Email, or anything else that communicates on the internet, expecially remote access services!

So from where I sit, I can’t understand how using vpn to tunnel terminal server will make my remote access more secure, in fact, possibly less secure. Please tell me if I am missing something though.

Thanks.

Greg

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Edit: 3/28/05

I have been talking about this issue with friends on forums, and I wanted to share more thoughts based on some of my posts. And just so you keep this in mind, I am basing these thoughts in the context of a small business with less than 50 users which might not even have an IT staff. A company like this typically will not spend $10-$15 thousand dollars on a VPN solution, leaving us with only the built in Microsoft technologies (or linux).

— from a post on 3/21/05 —

I dont think that vpn is less secure really, its got a great security model. What I think is less secure, is using vpn with TS. I dont believe it offers any additional protection. Why encrypt an encrypted connection? Why give access to the whole network and all the servers, if you only want them to access a few apps on 1 server? And why I think it’s less secure to run it this way? That is because the reason you run Terminal Server is to allow the user access to certain apps that would not otherwise run on a vpn, AND to isolate the use of those apps and their data. You cant isolate the processing of data and its transmissions on a vpn. The vpn essentially extends the internal network to a remote system over a public network, right? Well a TS client does not do that. It only extends the keyboard, mouse and graphics. So the data never leaves the network, it cant even be printed remotely or cut&pasted on the remote client (if you set that up of course).

So it’s not that I think vpn is less secure, implemented properly, it’s great, but only for the right purposes. For my systems, vpn wont work. I have to run apps that just wont run over a vpn, or they will but be so damn slow it just isnt practical. I installed vpn originally aboot 5 years ago at my largest client. We ran into many hurdles running our main apps. I basically determined that unless you have at least a 10 Mbit connection, dont bother. That’s not to say that apps cant work on vpn, it just depends on if they were written for it for one thing, and if not, how their execution and data is transfered. I have ran several apps that are so called ‘network’ apps, and all they do is put on a short cut to a large exe that is downloaded locally and then executed. That just wont work on vpn. It’s WAYYY too slow! Try running a 100mb + ms access mdb from remote vpn client, that then connects to a 3Gb + sql server db. Even on the fastest broadband connections, it just isnt feasible. Terminal Server solves that problem.

Now, also keep in mind, mostly why I have the ts’s is to do remote admin. Some companies have this setup: 2 servers, both are AD servers. One runs Exchange and IIS, and has MS ISA firewall on the server to vpn into and proxy out. (I didnt set that up, nor do I maintain it, I would have set it up way differently) The other server is behind that firewall and runs only a sql server internally. In this scenario, they didnt setup a dedicated firewall, and consequently are vulnerable from other sources that would put the domain controller at risk. This is because, it’s way more likely that IF an attempt were to be made to crack that server, it would be most open to attack on the IIS services, or Exchange. Once in, the firewall is useless. So… why put in the vpn here? There are so many WAY more insecure elements involved. This is why I mention in the blog… “if you’re worried about security, dont get online.” I mean, obviously your not THAT worried, or you wouldnt setup the systems that way. And if you’re not THAT worried, why use the VPN?

If I were to make the network more secure for remote admin I think I’d have to do this: Run a TS in a DMZ with admin rights to TS denied. (have to be a restricted use user acct.) Then, from the TS session, open another TS session to the specific server you want to administer. Your firewall can be set to allow communication on TS traffic to and from the dmz computer only. This way, no data is ever really sent to the remote pc, and the remote pc has not direct access to any internal system, but does have access to *view* information.

The insecurity I see, with both TS or VPN, is the client use and it’s vulnerabilities. They both suffer from the fact that IF some trojan is somehow executed and allows an unauth user remote control of the pc, that user could see all the data your company user can see. The advantage to TS in this situation, is that at least that ‘hacker’ would not have direct access to the whole network right from start. They could obviously run a keylogger and then log into that TS themselves, or from the remote pc. Same with the vpn. In my situation, the remote users use their own systems to remote into the company. They wont spend the money, nor do they have the administrative capability to maintain stringent policies and systems.

— Posted from 3/23/05 —

I found out that TS can be brute force attacked! (via password crack) (OH NO! VPN IS NEEDED!!) BUT!!!! Then I did a little more research and discovered that with my setup at my different clients, it aint gonna happen.

There is a program out there that can “dictionary attack” a Terminal Server. Not Brute Force it. There’s a difference. Dictionary attack uses a dictionary of words to test, brute force checks every letter combinatoin. That program must rely on the fact that the local “administrator” account always has local accees to the TS. And since it uses only a dictionary attack, dont use words for a password, it wont crack it. And since it relies on the admin account, rename the administrator to something else, problem solved.

Use of an 8 or more character password is also all that is needed to deter an actual brute force attack. Along with account lockout policies when logons fail, you can pretty much bet that you wont get brute force cracked. I read somewhere, that if you use 12 character passwords, and if they are only lower and uppercase, there are almost 400 BILLION BILLION combinations. And even if you could do 1 million attempts per second, it would take millions of years to crack! I am sure someone good at math can figure the details out. And this is all for just the password, YOU NEED A USERNAME TOO! Add lockouts to the mix, and it aint happening! Do some research on brute force cracking and you will see what I mean.

I read a post by someone who cracked a 6 character password with special characters in it, it was cracking something on the local machine (not networked then) and it took a day and a half to do it. Try doing that on network systems, where, if properly setup, will not allow millions of connection attempts like that.

I used to fear the “brute force” thing. Not now. And it’s not that it isnt possible, but properly configured networks/systems simply make it way too long to attempt it using current proccessing technology. that’s why higher bit encrytion is better. It takes way too much time to crack the encrypted key at 128 bits. By the time you did, the key would have changed.

Dictionary attacks are another thing, they can get a crack in minutes. But if you dont use dictionary words as passwords, then you are safe.

this all leads me to the essential wisdom of work, why do things the hard way. A hacker isnt going to try and crack something that is hard to get into, they will try the easiest route. TS and VPN are not easy to get into. They will look into which services provide the most exploits that are available to them. VPN and TS have very little exploits. (at least it was tough finding any) Try looking up exploits on your mail server or web server! I bet they’ll try getting in there way before an attempt on TS.

The amount of time involved to make these kind of attacks are huge. Script Kiddies or whatever arent going to spend that kind of time. The only way someone would do it is for money. And most likely a compititor might want the information and pay for the hacker, but holy cow, is that likely? I dont think so. It would be way easier to do some “social engineering” to infultrate the company and then get into the network.

Simple precautions on the TS are all that is needed. As with any service. 1. dont show the last user logged on. 2. restrict access to only certain users, not domain admins. 3. lockout failed login attempts. 4. long passwords 5. Change the admin name.

So I am still back to my original thought, vpn would not make ts more secure. It would only add more maintenance and head ache. But, if I already had a good vpn solution, I would utilize it.

However, I have a new thought, I guess. VPN, in certain situations that dont have stringent policies and procedures, would make remote access less secure than TS. This is because that encrypted tunnel does not get filtered by a firewall or IDS and a virus or attacker can use that connection to directly affect the entire network. With TS it is at least not possible. That’s why you have to have IT setup the remote computer and on it, restrict user actions as well. This makes VPN unattractive to me.

— and another post on 3/23/05 —

So when adding a vpn to tunnel a TS, what you are saying is, “I have a vpn, I need to tunnel it through another vpn to be more secure.” That’s like saying, “I need 2 firewalls to double up on the packet filtering.”

The only thing I think a vpn will do, and only if I had a nice hardware appliance type one, is give me device authentication. If I use MS software based vpn, especially using pptp protocol, I am no better off. I would still need to authenticate in either system (ts or vpn) and the hardware solution probably allows for IP or other device authentication. Also, I think that to really be secure you would need to use a certificate or something of that sort to authenticate. TS cant do that, so I would see that as an advantage in vpn.

If I put in a vpn, I open my whole network up. And with no real IT staff to monitor it or the client machine, that opens a whole mess of problems. At least with TS I prevent any openning of the network, only that port on that server. (no data is transfered, just user IO)

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In my situations, as in small businesses remote administration, I do believe VPN is openning a hole in the network and making it a little less secure than to provide straight access to Terminal Services. So far I have not seen any evidence to tell me otherwise, but if anyone out there can give me specific reasons to give me some evidence, please do.

  • Kevin

    Can you elaborate on what the differences are between using a VPN and remote access software? What are the advantages/disadvantages of both…or is one just a more dressed up version of the other?

    • Using a VPN would require you to essentially “Dial-up” a connection to your remote network. For example, you might be at home, and your work network has software on their end allowing you to connect to them. Using that established connection, you basically become a remote node on their network. (that’s one of the main reasons I don’t like VPN’s.)

      Using a remote access solution is different, although technically they are still creating some sort of a tunnel for you to securely connect. The difference is, you are not connected as a remote computer on the work network, you are only making a very specific secure connection to a specific port and specific computer. Not the same as a VPN tunnel, where you basically open up all ports and re-route your communications to the work net. What I prefer is a program like GoToMyPC, or my favorite, LogMeIn.com. They act as a third party to “broker” a connection from your home system to the work system. They do this in an outbound-connection only scenario. What I mean by that is, you don’t open ports up on a firewall and re-route traffic to certain internal systems. (another security hole, possibly) In the LogMeIn setup, it makes an outbound connection without any inward firewall rules. You connect at home to LogMeIN, they know where the work computers is, and they create the connections between the two for you. IMHO, more secure that way.

      Does that help? I am not familiar with proxynetworks, but it looks like some similar connection methods as GoToMyPC or LogMeIn.

      I might add too, that even though you would still create an inward connection with a firewall rule, I would still greatly prefer an SSH tunnel to another internal system. Like creating your SSH connection with a port forward to RDP on your work desktop. (I wrote a program to do that actually!) But since I’ve discovered LogMeIn, I prefer that the most, it’s just way to easy, no servers and firewalls to manage at the work end. But no matter what, unless there is an actual practical requirement for using a VPN (and I can’t think of one that SSH can’t handle, in regards to remote access), I stay far away from VPN’s. That is, unless you desire to connect to remote networks, then sure, VPN sounds great.

  • James Roger

    “Who said VPN is not secured? VPN creates a private tunnel between you computer and organization which is secured and encrypted. However, VPN is costly as compared to remote access tools like logmein, R-HUB remote support server, teamviewer etc.”