[ale] nasty UPNP bug allows EXTERNAL hackers INTERNAL access

Thu Feb 7 18:06:57 EST 2013

Thanks, Ron! Our main network was fine, but the little D-Link wireless 
router we have hanging outside the firewall for guest Internet access 
did have the flaw. I had to both update the firmware, and then I had to 
completely disable UPnP.  I still couldn't just disable the external 
UPnP. Of course, in our case we don't really want guests modifying the 
config on the router anyway, but it's disgusting that there's still no 
fix to just block external UPnP to this day.

Scott

On 2/7/2013 3:06 PM, Ron Frazier (ALE) wrote:
> Hi all,
>
> I wanted to let you know about a nasty bug in the UPNP implementation 
> of millions of routers.  This could allow an external hacker free and 
> open access to your internal network.  I think this mainly applies to 
> home and small office routers, but this could apply to commercial ones 
> as well.
>
> UPNP stands for Universal Plug and Play.  It is a feature of almost 
> all routers that is usually on by default.  It allows things INTERNAL 
> to your network, like XBox game systems, Skype, DVR's and other things 
> to OPEN HOLES for incoming communications through your firewall, 
> usually without your knowledge or permission, and sometimes without 
> your ability to monitor or control it.  This is designed to allow 
> gamers, for example, to instantly participate in network gaming 
> without configuring the router.  It generally doesn't require 
> authentication, and assumes anyone making a UPNP request from within 
> your network is trustworthy.  This, in itself, is somewhat of a 
> security risk, and I've had UPNP turned off for years on my routers.  
> It's one of the first things I disable when I set up a router, since I 
> have no need for it.
>
> They discussed the new issue, which is much much worse, on the last 
> two Security Now podcasts.
>
> http://twit.tv/sn
> http://twit.tv/show/security-now/389
> https://www.youtube.com/watch?v=wEa43qM4JjQ#t=09m44s  (Youtube video 
> of 389.  Relevant part starts at 09:44.)
> http://media.grc.com/sn/sn-389.mp3 - MP3 audio of 389.
> http://twit.tv/show/security-now/390
> http://www.grc.com/securitynow.htm  (Episode 390 hasn't been posted 
> here yet, but should be shortly.)
>
> UPNP was always intended to be used only on your INTERNAL LAN.  It was 
> never intended to be exposed on the Internet on the WAN.  A group of 
> security researchers at Rapid7 spent months last year using bots to 
> probe EVERY routable IPv4 address on the Internet. They sent UDP UPNP 
> discovery packets to every address several times.  The results of the 
> probes were both surprising and very disconcerting.
>
> They found that 2.2% of ALL IPv4 routers exposed to the internet 
> responded to UPNP discovery requests.  This corresponds to 81 MILLION 
> routers.  This means that they are exposing the UPNP service to the 
> EXTERNAL internet at large.  This is a MAJOR security flaw.  Of those, 
> 20%, or 16.2 MILLION are exposing their SOAP API to the EXTERNAL 
> internet at large.
>
> This means that a REMOTE cracker, just by sending a few UDP packets to 
> your router's EXTERNAL address, can punch holes in your firewall and 
> break into your INTERNAL LAN just as though he was your XBOX sitting 
> in your house.  It requires no authentication or decryption on the 
> cracker's part, and is trivially easy.
>
> This is very bad news for the 81 million people, most of which, don't 
> even know they are vulnerable.
>
> For years, Steve Gibson has been operating the Shields Up service on 
> his website.  It provides a way to scan your network from the outside 
> to see if net bios is being exposed, or if common TCP service ports 
> are being exposed.  In light of these events, he has added testing for 
> the UPNP vulnerability.
>
> I would recommend that each person reading this make use of Steve's 
> port scanner to test your router's external IPv4 address to determine 
> if you are vulnerable to the UPNP attack vector. Here's how.
>
> Go to the Shields Up main page at: https://www.grc.com/x/ne.dll?bh0bkyd2
>
> You will probably have to trust grc.com in noscript, etc. for 
> everything to work.  Read what it says there and click proceed. Keep 
> in mind, some of the verbiage is a decade old, but the site is still 
> very useful.  The stuff related to UPNP is new.
>
> Once you're on the second page, you will get to a screen with some 
> menu buttons on it.
>
> Click the orange GRC's Instant UPNP Exposure Test button.
>
> His server will query the UPNP ports for your external IPv4 address.  
> It will then report back as to whether your router didn't respond at 
> all (PREFERABLE), actively rejected the remote request (OK), or did 
> respond to the UPNP discovery request (BAD). The result page also 
> contains verbiage explaining the results.
>
> Note that a simple port scan, like from nmap, will not do the trick 
> here.  First, you have to send the scan from outside your router, on 
> the internet side.  Second, the UPNP discovery request is a 
> specifically formatted UDP packet, not just a simple ping. Since it's 
> UDP, the source address can be spoofed by a cracker.
>
> If your router is in the category that did respond, you are 
> potentially vulnerable to attack.  At the very least, a cracker could 
> find out that your UPNP service is listening on the WAN, and it will 
> probably tell him which UPNP stack you have in its reply. This may 
> give him the info he needs to attack you.  If your router is among the 
> 1 in 5 (of the 81 million) that exposes its SOAP API to the WAN, you 
> are vulnerable to immediate attack.  If your router responds to an 
> external UPNP request, which it NEVER should, you should find a way to 
> turn off that functionality and retest it.  If you cannot turn it off, 
> you should discontinue using this router.
>
> While you're there on the Shields Up page, you can select other 
> buttons as follows:
>
> File Sharing - tests to see if your router is exposing any net bios 
> file sharing ports to the WAN.
> Common Ports - tests to see if certain commonly used TCP service ports 
> are listening on the WAN.
> All Service Ports - tests to see if the first 1056 TCP service ports 
> are listening on the WAN
> User Specified Custom Port Probe - used to test a specific TCP port 
> number after entering it into the blank.
> Lookup Specific Port Information - used to lookup data about what 
> certain port numbers are commonly used for.
>
> Here are other resources that Steve provides relative to the UPNP 
> problem so you can research it:
>
> https://community.rapid7.com/servlet/JiveServlet/download/2150-1-16596/SecurityFlawsUPnP.pdf 
>
> http://toor.do/DEFCON-19-Garcia-UPnP-Mapping-WP.pdf
> http://www.upnp-hacks.org/upnp.html
> http://toor.do/upnp.html
> http://www.h-online.com/security/news/item/Millions-of-devices-vulnerable-via-UPnP-Update-1794032.html 
>
>
> I recommend that you test your internet facing IPv4 addresses for UPNP 
> vulnerability immediately.  If your router responds to the external 
> UPNP inquiry, I suggest turning off UPNP from its control panel and 
> retesting.  If it still responds, consider upgrading the firmware and 
> retesting, or removing and replacing the router.
>
> I hope you find this information useful.
>
> Sincerely,
>
> Ron
>
>