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I'm trying to figure out the risks of running RDP over the internet, using two windows 10 professional stations, and if a VPN is absolutely necessary to achieve good security.

From the information I found so far on the net, a leak was discovered in 2012 that allowed the creation of exploits to intercept an RDP session. I understand this leak was closed in the meantime and that you were always protected if you used Network Level Authentication (NLA).

Most other security issues seem to be focused on the client side, i.e. when connecting to an untrusted RDP session with the main purpose of stealing a user's credentials.

If we assume the following situation:

  • Windows 10 Professional used on host and client side
  • Host side with fixed IP, no DNS involved to establish connection
  • NLA used
  • Strong passwords used, changed monthly, Administrator account not active
  • Host machine contains confidential information

Would you not feel comfortable enough? Where do you see the biggest risk as opposed to a connection over VPN? And is there a way to increase security of the RDP connection without resorting to VPN?

  • Can you give us a sense of why you don't want to use a VPN? – Graham Hill Nov 14 '15 at 19:05
  • It's not that I specifically don't want to have VPN, I would just like to understand the difference in security and if this difference justifies the installation and maintenance of additional tools. – vic Nov 14 '15 at 21:24
  • main practical risk is likely to be account lockout (assuming predictable usernames), or password re-use (one of your "strong" passwords gets used by a user at another site), + the risk of 0-day/unpatched issues in RDP. Whether these are a realistic concern likely depends on your threat model... – Rоry McCune Nov 16 '15 at 12:42
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    Thanks. Considering that you could have a 0-day risk with VPN, too, and the other two points wouldn't bother me too much, I guess I would not be overly concerned. – vic Nov 16 '15 at 12:52
  • ooh I forgot there's also a small info. leak inevitably when you put RDP on the Internet , which is it'll expose the valid login contexts for the system (e.g. the local system name, the AD domain) – Rоry McCune Nov 16 '15 at 13:01
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I advise against exposing internal servers directly to the Internet.

Remote code execution vulnerabilities crop up too frequently for comfort and direct exposure of internal hosts.

That said you can mitigate the risks somewhat with a few steps (these are not alternatives, they are layered complementary defenses):

  1. Perimeter firewall enforcing white list of source IPs specifically to tcp/3389 on the Windows host or hosts
  2. Windows firewall on each of the Windows hosts enforcing white list of source IPs specifically to tcp/3389 on localhost
  3. Either: use Remote Desktop Gateways as bastion hosts in your DMZ that are on a separate domain and put the similar restriction to 1 and 2 between DMZ and internal
  4. OR: use SSH bastion hosts and port forwarding as above if RDG isn't a good option

These steps substantially reduce the exposure to reconnaissance or attack

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    I would replace #3 with: using RD Gateway, and this is not optional or a bonus: This is super-important. A whole nice set of security policies can be applied to it, isolate internal hosts properly, good restrictions, etc. This give much of the value of a VPN, without actually using a VPN. @vic should definitely use a RDG, and have the perimeter firewall restrict access to that server alone. – AviD Nov 16 '15 at 21:12
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    Problem in my specific case is that my server infrastructure is all *nix, so while I'd love to use a RDG, it doesn't seem possible at the time. – vic Nov 16 '15 at 21:24
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    @Alain O'Dea - What would your views be on limiting IP addresses that can access services via RDP? How easy or difficult would it be to spoof these? – Motivated Apr 13 '16 at 18:06
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    @Alain O'Dea - What do you mean by 'close in'? – Motivated Apr 14 '16 at 5:01
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    @Alain O'Dea - Thanks. You mentioned that ` IP spoofing isn't very practical with TCP protocols like RDP unless the attacker is close in`. Is there an authoritative sources that describes this further? I am attempting to convey this to senior management as there is plenty of FUD regarding it. – Motivated Apr 14 '16 at 17:37
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There are a few ways to protect RDP.

  • Best practice is don't use public port #3389. Translate it to something different. Is the best way to decrease hack attempts.
  • Allow only certain IPs(or range of IPs) address to public IP. Use smart routers. I use mikrotik (http://wiki.mikrotik.com/wiki/Bruteforce_login_prevention) or Cisco.
  • Configure firewall blocking to many attempts. I use third party tools to block the traffic. A free tools is from www.bfguard.com. There are several more but I like this one because it free. This tool analyzes event logs for failed logins and then add IP to windows firewall for blocking.
  • Last as it is more complex but not bad is to setup a VPN. There is few ways to do so.
    1. Use built in windows VPN server
    2. Use your router's functionality. Most of betters routers has it built in to.
    3. Setup separate access server like OpenVPN, Mikrotik, or some linux based....
  • Consider to encrypt your sensitive data using secondary password with bitlocker on secondary drive which could be virtual disk stored on primary disk.
  • Use random username with strong password. You can check your password and username leaked passwords list
  • The link you just added gives me a Could not connect: Network is unreachable error message. – kasperd Nov 26 '16 at 11:52
  • Turns out wiki.skullsecurity.org responds with RST on port 443. But because the domain is dual stack I got a misleading error message from the browser. It never told me about the RST from the server, which is the real problem. – kasperd Nov 26 '16 at 12:11

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