RDP and the Critical Server Attack Surface
MS12-020, a use-after-free discovered by Luigi Auriemma, is roiling the Information Security community something fierce. That’s somewhat to be expected — this is a genuinely nasty bug. But if there’s one thing that’s not acceptable, it’s the victim shaming.
As people who know me, know well, nothing really gets my hackles up like blaming the victims of the cybersecurity crisis. “Who could possibly be so stupid as to put RDP on the open Internet”, they ask. Well, here’s some actual data:
On 16-Mar-2012, I initiated a scan across approximately 8.3% of the Internet (300M IPs were probed; the scan is ongoing). 415K of ~300M IP addresses showed evidence of speaking the RDP protocol (about twice as many had listeners on 3389/tcp — always be sure to speak a bit of the protocol before citing connectivity!)
Extrapolating from this sample, we can see that there’s approximately five million RDP endpoints on the Internet today.
Now, some subset of these endpoints are patched, and some (very small) subset of these endpoints aren’t actually the Microsoft Terminal Services code at all. But it’s pretty clear that, yes, RDP is actually an enormously deployed service, across most networks in the world (21767 of 57344 /16′s, at 8.3% coverage).
There’s something larger going on, and it’s the relevance of a bug on what can be possibly called the Critical Server Attack Surface. Not all bugs are equally dangerous because not all code is equally deployed. Some flaws are simply more accessible than others, and RDP — as the primary mechanism by which Windows systems are remotely administered — is a lot more accessible than a lot of people were aware of.
I think, if I had to enumerate the CSAS for the global Internet, it would look something like (in no particular order — thanks Chris Eng, The Grugq!):
- HTTP (Apache, Apache2, IIS, maybe nginx)
- Web Languages (ASPX, ASP, PHP, maybe some parts of Perl/Python. Maybe rails.)
- TCP/IP (Windows 2000/2003/2008 Server, Linux, FreeBSD, IOS)
- XML (libxml, MSXML3/4/6)
- SSL (OpenSSL, CryptoAPI, maybe NSS)
- SSH (OpenSSH, maybe dropbear)
telnet (bsd telnet, linux telnet)(not enough endpoints)
- RDP (Terminal Services)
- DNS (BIND9, maybe BIND8, MSDNS, Unbound, NSD)
- SMTP (Sendmail, Postfix, Exchange, Qmail, whatever GMail/Hotmail/Yahoo run)
I haven’t exactly figured out where the line is — certainly we might want to consider web frameworks like Drupal and WordPress, FTP daemons, printers, VoIP endpoints and SMB daemons, not to mention the bouillabaisse that is the pitiful state of VPNs all the way into 2012 — but the combination of “unfirewalled from the Internet” and “more than 1M endpoints” is a decent rule of thumb. Where people are maybe blind, is in the dramatic underestimation of just how many Microsoft shops there really are out there.
We actually had the opposite situation a little while ago, with this widely discussed bug in telnet. Telnet was the old way Unix servers were maintained on the Internet. SSH rather completely supplanted it, however — the actual data revealed only 180K servers left, with but 20K even potentially vulnerable.
RDP’s just on a different scale.
I’ve got more to say about this, but for now it’s important to get these numbers out there. There’s a very good chance that your network is exposing some RDP surface. If you have any sort of crisis response policy, and you aren’t completely sure you’re safe from the RDP vulnerability, I advise you to invoke it as soon as possible.
(Disclosure: I do some work with Microsoft from time to time. This is obviously being written in my personal context.)