Cyber101: De-Worming Windows

A reader asked earlier today:

“The news is talking about a new threat on Windows machines that can spread like the WannaCry attack did. Is it real, and what can I do about it?”

It’s very real. Microsoft released guidance via their TechNet website ([Prevent a worm by updating Remote Desktop Services (CVE-2019-0708) – MSRC] that detailed a newly discovered vulnerability in versions of Windows Server 2008 R2 and earlier as well as Windows 7 and earlier on the desktop side.  Here’s what you need to know:

The vulnerability concerns Remote Desktop services – basically a way to get to a Windows Server or desktop from somewhere other than a keyboard, mouse, and monitor plugged into the machine. This is very popular and used to remotely administer servers found in Cloud environments, virtual environments, datacenters that are in different physical locations, etc. It’s also used for remote administration and technical support for desktops where the IT staff may be physically in a different location than the user (like support for telecommuters and multiple office locations). Because of the usefulness of the Remote Desktop Protocol (RDP) system, most Windows Servers and a large number of desktops will have it turned on.

To be clear, the vulnerability isn’t in RDP itself. That set of services is still considered secure. The vulnerability is found in the process of accessing RDP, where the remote machine and the local machine communicate with each other before anyone is asked for a username and password. Due to the nature of this vulnerability, a threat actor can perform tasks like installing software or causing damage to systems even if they do not have a valid set of credentials (username/password/second factor) for the machine in question. The cybersecurity industry uses the term “wormable” to describe this kind of vulnerability, since not requiring credentials means that malware that leverages this flaw in the code could spread itself. We’ve seen some examples of this, such as with the WannaCry outbreak not that long ago, where the malware spread itself from system to system without any user interaction to make it happen. Once one system is infected, any other system the infected machine can communicate with becomes a target and, if the second machine is vulnerable, it becomes infected. This process continues until someone figures out how to stop the malware, or the malware runs out of infectable machines.

There are some indications that we may be seeing threat actors beginning to use this particular vulnerability already, so addressing it has become a vital concern. The good news is that there are steps you can take to protect your systems:

First, you should know that Microsoft has released a patch for no-longer-supported versions of Windows, specifically Windows XP and Windows Server 2003 and 2003 R2. This has only happened once before, and indicates that Microsoft is extraordinarily concerned that this vulnerability can and will be exploited – to the point where they feel the must correct the problem – even on Operating Systems they no longer support at all. Of course, patches are available for Windows 7 and Server 2008 and 2008 R2; which are still under support by Microsoft.  You should immediately patch all systems (see the link above to get the patches) that are vulnerable to this attack vector. Later versions of Windows desktop and Server (8 or higher on desktop, 2012 and higher on Server) are not impacted, but all earlier versions must be patched immediately.

If servers cannot be patched, for whatever reason, then the safest course of action is to disable RDP services on the servers that are vulnerable and to block networking port 3389 – the default digital connection point used to access RDP – at your network firewall. Reach out to your IT staff and/or your 3rd-party IT provider for help with this task.

This vulnerability is real, and very dangerous because it can allow an attack to propagate all by itself. It can be defended against, however, with patching wherever possible and blocking the attack vector by disabling RDP everywhere else. Please reach out to your SKOUT Security Operations Center and Customer Success Team members if you are a customer of SKOUT Cybersecurity, we’re more than happy to assist in keeping your systems safe from this threat.