How secure is TeamViewer for simple remote support?

Question

I'm deploying a web-based ERP system for a customer, such that both the server and the client machines will be inside the customer's intranet. I was advised in another question not to use TeamViewer to access the server, using more secure means instead, and so did I. But now I'm concerned about whether or not TeamViewer would be appropriate for the client machines, which are not "special" to this system in particular, but nonetheless I don't want to lower their current security, neither I want to compromise the computer on my end.

My question, then, is whether or not TeamViewer is "good enough" for simple remote desktop support, where it will be used simply to assist the users in the usage of the system, and whether or not I must take additional measures (like changing the default settings, changing the firewall, etc) to reach a satisfactory level or security.

Some details:

1. I already read the company's security statement and in my non-expert opinion all's fine. However, this answer in that other question has put me in doubt. After some research, UPnP in particular does not worry me anymore, since the feature that uses it - DirectIn - is disabled by default. But I wonder if there are more things I should be aware of that's not covered in that document.

2. The Wikipedia article about TeamViewer says the Linux port uses Wine. AFAIK that doesn't affect it's network security, is that correct?

3. Ultimatly, the responsibility of securing my customers' networks is not mine, it's theirs. But I need to advise them about the possibilities of setting up this system, in particular because most of them are small-medium NGOs without any IT staff of their own. Often I won't be able to offer an "ideal" setup, but at least I wanna be able to give advice like: "if you're installing TeamViewer in this machine, you won't be able to do X, Y and Z in it, because I'll disable it"; or: "you can install TeamViewer in any regular machine you want, it's safe in its default configuration; only this one *points to server* is off-limits".

4. My choice of TeamViewer was solely because it was straightforward to install in both Windows and Linux machines, and it just works (its cost is accessible too). But I'm open for other suggestions. I'm low both in budget and specialized staff, so I'm going for the simpler tools, but I wanna make a conscious decision whatever that is.

Answer 1

There's a couple of differences between using a 3rd party supplier (such as teamviewer) and a direct remote control solution (eg, VNC)

Team Viewer has advantages in that it doesn't require ports to be opened on the firewall for inbound connections, which removes a potential point of attack. For example if you have something like VNC listening (and it isn't possible to restrict source IP addresses for connections) then if there is a security vulnerability in VNC, or a weak password is used, then there is a risk that an attacker could use this mechanism to attack your customer.

However there is a trade-off for this, which is that you're providing a level of trust to the people who create and run the service (in this case teamviewer). If their product or servers are compromised, then it's possible that an attacker would be able to use that to attack anyone using the service. One thing to consider is that if you're a paying customer of the service, you may have some contractual come-back if they're hacked (although that's very likely to depend on the service in question and a whole load of other factors)

Like everything in security it's a trade-off. If you have a decently secure remote control product and manage and control it well then I'd be inclined to say that that's likely to be a more secure option than relying on a 3rd party of any kind.

That said if the claims on TeamViewers website are accurate it seems likely that they're paying a fair degree of attention to security, and also you could consider that if someone hacks TeamViewer (who have a pretty large number of customers) what's the chance that they'll attack you :)

Answer 2

Take a look at this security analysis of TeamViewer. In short, it's definitely not secure on untrusted networks: https://www.optiv.com/blog/teamviewer-authentication-protocol-part-1-of-3

Conclusion:

It is my recommendation that TeamViewer not be used on an untrusted network, or with the default password settings. TeamViewer does support increasing the password strength to a configurable length, and using alphanumeric passcodes, but it’s unlikely that casual users will have changed this setting.Keep in mind that there is a substantial attack surface in TeamViewer that needs more analysis such as the unauthenticated, plaintext communication between client to server (over 100 commands are supported and parsed on the client side), as well as many peer-to-peer commands, routed through the gateway server. Despite the danger to this much exposed attack surface, the risk is somewhat mitigated by an extensive use of std::string and std::vector instead of C-style strings and arrays.

Answer 3

I just want to add an answer which I think hasn't been touched upon yet. When you connect via teamviewer to another computer, you share your clipboard with that computer (by default).

Therefore, everything you copy onto your clipboard is also copied onto the clipboard of the computer you are connected to. By installing a clipboard tracking application such as ClipDiary, on the host computer, you can keep a record of everything copied onto the clipboard by the person connecting to you.

Most of the answers here are focusing on the security of the computer being used as the host, but this is also a potential security issue for the computer connecting to the host, especially if you use a password management tool such as KeePass, as the host computer could potentially have a record of usernames and passwords (and potentially URL's if you also copy the URL from KeePass to your browser) on the clipboard history after your session is over.

Answer 4

I don't know enough about TeamViewer to give you an assessment of its risks or whether it is a good choice for your situation. But I'm going to re-iterate a comment from @Lie Ryan. If you deploy TeamViewer for this purpose, one potential way to reduce the risk of remote attacks is to set up a firewall (on both endpoints) which blocks all access to the TeamViewer ports except from authorized machines.

Answer 5

About TeamViewer, there are a couple things that I think you should keep in mind:

• You can't easily look at the source and verify its security, and it's a network-facing attack surface. That's not so nice – if you're able to make an OpenSSH server with password-based auth deactivated the internet-facing part instead, do that. (You might want to give the user a method to start/stop the server.) Through the OpenSSH tunnel, you could just use localhost-bound VNC to connect to the display. Of course, this method doesn't work so well if the PCs in question are behind a NAT/overzealous Firewall and you don't have a way to get behind that firewall. Ideas to get around it:
  • You could use a hack like http://samy.pl/pwnat/ to open them up to connections from the internet.
  • You could do the SSH tunnel in the reverse direction: When they want support, they start a script that makes an SSH tunnel to your support server and connects a TCP connection to the VNC server to the SSH connection. Your support server has the client's public key in its authorized_keys file with a forced command that connects the client to your reverse VNC client.
• If you use it, make sure to never have a system running with that stupid 4-digit passcode system. Yes, they do have exponential lockout times, but first thing, you don't want support to be locked out that easily and second thing, well, what if someone just tries one random combination on 100000 PC running teamviewer? He'll get ~100 established connections without running into any lockout, I think – afaik, the lockout is completely client-side.

Answer 6

Teamviewer is not secure period. Think about it. Teamviewer can be configured to always use the same Partner ID and password. Similar code can be created and launched just by the user clicking on an email. Great tool? Absolutely..for guys like me who support a large bunch of remote users who can't tell a colon from a semi-colon. But secure? No way No how. Teamviewer allows remote access to a PC and can circumvent Cisco VPN or any other VPN security. This crap about the end user having to give out the partner ID and pass is just that...crap. This can be gotten around very easily. Don't get me wrong. I like Teamviewer. But don't kid yourself, it's not secure at all.

Answer 7

I would suggest a native solution such as VNC, enabling you to omit such workarounds as TeamViewer in WINE etc, as well as using the local operating systems package management utility to ensure that the solution stays up to date. For security, use an SSH tunnel. This ensures that all VNC communications are encrypted, including the initial VNC auth/password handshake. This is especially important as a lot of VNC implementations are rather insecure.

In addition as another respondant suggested, use IP filtering to ensure that only those at certain addresses are able to communicate with the VNC server.

Answer 8

One way we handle it: if client requests TeamViewer availability, user starts TeamViewer on demand and admin kills it upon tasks completion. Another solution we once deployed in such a case, is that TeamViewer is started from an SSH session by the admin. Alternatively, you might look into "invite-me" desktop sharing tools. Or my favorite: mirroring the Xsession via SSH to your desktop.

Answer 9

Teamviewer gives the computer user the ability to give a remote session to is PC to anyone in the internet. So, the security of the network passes to the end-user! That's a no-go. I advise you to use VNC.