Steve Riley on Security : wireless

Ethernet and WiFi and Bluetooth, oh my!

Steve Riley — Thu, 16 Oct 2008 00:16:48 GMT

Customers have long requested a way to configure a computer to automatically disable its wireless NIC when its Ethernet is in use. Many third-party utilities can do this for you, but neither XP nor Vista have a built-in way to accomplish this, nor will Windows 7. Although having both NICs enabled first appears to cause a security issue, in reality that would be true only if both of the following were also true:

The user is logged on as a local administrator
The user, or some code the user runs, enables IP routing

By default, all forms of IP routing (including NIC bridging) are disabled. Only local administrators (or group policy) can enable them. So the risk, actually, is minimal.

If you have a stroll through group policy, you'll discover this setting: "Prohibit installation and configuration of Network Bridge on your DNS domain network" (more here, here). This setting allows you turn a computer into a router that bridges two networks. The bridging works only when one of the interfaces is in the same DNS namespace it was in when the bridge setting was enabled, and it works only when the Windows firewall is disabled on both interfaces (never a good idea). Additionally, regardless of the group policy setting, the function doesn’t even appear as an option when the user is logged in as a non-admin. The group policy setting simply removes the option from people who are local admins of their computers. So here's a way you can remove the ability even for local admins to enable routing.

However, let me admit that I wish we did have a way to implement your request, but for an entirely different reason: IP address preservation. Consider what happens when I'm on my own corpnet in my office. I put my laptop in its dock, which is connected to the Ethernet. I never bother disabling my wireless (I'm lazy). So whenever I'm in my office I'm taking up two IP addresses: one on the Ethernet and one on the wireless. Such wasteful profligacy, I know! (Note this isn’t a problem for any Bluetooth adapter, which always uses APIPA in its default configuration; I can’t imagine a scenario where you’d want Bluetooth to use DHCP.)

If you agree with me that this is something we should address post Windows 7, not for "security" reasons but as a good general networking practice of being conservative with address allocation, please speak up. Now's the time for your input.

[OT rant] Are there any home WiFi routers that DON'T SUCK?

Steve Riley — Sat, 23 Aug 2008 03:12:38 GMT

Warning: rant ahead, and names named.

When I'm not traveling, I like to work from home some days rather than endure the trek from Seattle to Redmond (although it's much better now that our own employee transit service has expanded into my neighborhood -- the existence of which is sad commentary on the availability and reliability of Seattle's public transit companies).

This means, of course, that I need fast and stable network connections. Comcast with their PowerBoost is working very well for me. But I just can't find a decent wireless router at all. My Lenovo T61p (with Intel 4965abgn adapter) just won't stay connected to my D-Link DIR-628 and IT'S DRIVING ME CRAZY! (Yes, I've tried various driver versions, from both Lenovo and Intel.)

My house is in an area with a lot of wireless activity -- sometimes I can see nine or ten SSIDs. I'm running draft N on 2.4GHz (which occupies two non-adjacent channels, currently 1 and 4), and I suspect the problem is collision interference. I could shift the router to 5.2GHz, which I probably would help, but then the rest of the computers in my house won't connect. Why, you ask? Well get this: the DIR-628 is part of D-Link's RangeBooster N family. So I stayed in the family and got two DWA-542 adapters for the desktop computers. Yet they only do 2.4GHz! Silly me, I assumed that being in the same family means full support of the router's capabilities.

I'm very tempted to replace my router again -- and I'm thinking that the best option is to get one with dual radios. That way I can move my T61p to 5.2GHz and replace the desktop adapters, while still having single-channel 802.11b/g on 2.4GHz for the Wii and my PlayStation Portable.

Now my request: tell me about your experience with home routers. What do you really like, and why? What should I buy?

Myth vs. reality: Wireless SSIDs

Steve Riley — Tue, 16 Oct 2007 10:08:58 GMT

Do you ever wonder sometimes how it is that some ideas just won't die? Like the thought that not broadcasting your wireless network's SSID will somehow make you more secure? This is a myth that needs to be forcibly dragged out behind the woodshed, strangled until it wheezes its last labored breath, then shot several times for good measure.

Folks, there are fundamental differences between names, which are public claims of identities, and authenticators, which are secrets used to prove identities, and I've written extensively about this before. An SSID is a network name, not -- I repeat, not -- a password. A wireless network has an SSID to distinguish it from other wireless networks in the vicinity. The SSID was never designed to be hidden, and therefore won't provide your network with any kind of protection if you try to hide it. It's a violation of the 802.11 specification to keep your SSID hidden; the 802.11i specification amendment (which defines WPA2, discussed later) even states that a computer can refuse to communicate with an access point that doesn't broadcast its SSID. And, even if you think your SSID is hidden, it really isn't. Let me explain.

All 802.11 wireless networks, regardless of the kind of operating system or encryption you might use, also emit unencrypted frames at times. One kind of unencrypted frame is an association frame. This is what a client computer, or "supplicant" in the 802.11 protocol vernacular, emits when it wants to join a wireless network. Contained within the frame, in clear text of course (since the frame is unencrypted), is the SSID of the network the supplicant wants to join.

Both Windows XP and Vista work best when your access points broadcast their SSIDs. XP really doesn't behave well at all with nonbroadcasting SSIDs. Vista has some added smarts to improve this a bit. Normally, Vista continually sends probe requests for nonbroadcasting networks. These probes are similar to unencrypted 802.11 association frames, and will generate clear-text responses from the access points if a nonbroadcasting network is present. You can reduce, but not entirely eliminate, these probes by configuring the wireless client to probe only for automatically-connected nonbroadcasting networks.

Both these behaviors make it very easy for an attacker to discover your SSID. The bad guy, perhaps a contractor or a guest in your facility, could run one of many wireless sniffer programs and simply capture the hundreds of association frames or probes that litter your air. No amount of "hiding" configured in your access points can prevent this kind of traffic interception.

So there you have it, simple SSID discovery. The old axiom remains true: security by obscurity is no security at all. Hiding an SSID will not hide a wireless network, so ignore any such advice -- and it's amazing how often I continue to see this. By the way, also ignore any advice that says to use MAC address filtering. It's amazingly trivial to spoof the MAC address of an allowed supplicant -- simply sniff the traffic, look at the MAC addresses, and use the neat little SMAC utility to change your MAC to one that's permitted.

Nonbroadcasting networks are not secure networks. The right way to secure a wireless network is to use protocols that are designed specifically to address wireless network threats. If you're still using WEP, either static or dynamic, I encourage you to move to WPA2 as soon as possible. For those of you at home running XP and have kept it updated, or if you're running Vista, then, you simply need to enable WPA2. We've got some additional guidance for home/small offices and for enterprise networks with certificate services or without. If you have hardware that's more than two years old and you can't upgrade it, check to see whether it supports WPA (an interim specification released before WPA2 was ratified). Both WPA and WPA2 are built on sound cryptographic principles, they're proven in the field, and they'll keep the bad guys out -- even when you're broadcasting your SSID to the world.

What motivates a journalist?

Steve Riley — Thu, 19 Jan 2006 02:52:00 GMT

OK, I have to unload a burden here.

I often interact with the tech press in various places throughout the world. I've had wonderful, productive meetings with many fine journalists. New Zealand and Malaysia particularly stand out in my memory. However, a thing has happened today that, while not affecting my relationships with individual journalists, irritates me about tech reporting in general.

Take a look at this: "Windows Wi-Fi patch could be a long time in coming." It describes a "vulnerability" recently reported by a researcher at a security conference. c|net also wrote about this two days ago.

I'm disappointed at the seemingly superficial reporting here. Mark Loveless (the researcher) has discovered a way to confuse unsuspecting people simply by taking advantage of a feature in Windows. He has not discovered a vulnerability. There's no error in either code or the default configuration here.

Today's article implies that a bad guy can get access to any system he wants to. Thing is, the default configuration won't permit that. You have to run as local admin and deliberately misconfigure your wireless settings for a bad guy to connect to your computer -- and when you do this, Windows warns you multiple times about potential threats.

It saddens me that, rather than truly analyzing the researcher's report, the journalist simply chose to report "yet another vulnerability."

How to secure your wireless network

Steve Riley — Sat, 12 Nov 2005 10:43:00 GMT

I'm now a contributing editor for TechNet Magazine. Everyone with a TechNet subscription automatically receives it; if you don't have one, you can still get the magazine free. The magazine's published three issues so far: Winter 2005, Spring 2005, and November-December 2005. You'll especially enjoy the "Hacking" series in the first issue, where Jesper writes up his "Anatomy of a hack" conference session that always seems to score a hundredth of a point or so higher than me! (LOL) Good news: the magazine is increasing its frequency; it'll be bimonthly through June 2006, then monthly after that.

Anyway, in the November-December 2005 issue, I've co-written (note I don't say "co-authored"; "author" is not a verb!) with Kathryn Tewson an article on wireless security for the Security Watch column. We describe the threat, some wireless security basics, how not to secure a wireless network (hint: bogus advice regarding SSIDs and MAC addresses figures prominently here), and details on access control and encryption. We also describe three common scenarios.

Read through the article for information on the various technologies and our recommendations -- which is pretty simple these days: WPA or WPA2 are really the only logical choices. While you're at it, subscribe to the magazine, too. I think you'll enjoy it. Look for more articles of mine in the magazine over time; for the January-February 2006 issue, I'll have an article describing VPN quarantine (just sent it to the editors today, actually).

August article: 802.1X on wired networks considered harmful

Steve Riley — Thu, 11 Aug 2005 20:55:00 GMT

Several months ago I learned from Svyatoslav Pidgorny, Microsoft MVP for security, about a problem in 802.1X that makes it essentially useless for protecting wired networks from rogue machines. Initially I was a bit skeptical, but the attack he described is in fact true -- I've seen it myself now. So I've been explaining the attack at conferences lately and have also included information about it in the book. However, I don't believe the danger presented by wired 802.1X is getting enough reach, so I've written about it in the August security management column.

As you read the article, remember that the vulnerability enabling the attack is a fundamental weakness in the protocol -- it authenticates only upon connection establishment and assumes all traffic after authentication is legitimate. The vulnerabiliy exists in wired networks because there's no follow-on packet authentication. You really should be using domain isloation with IPsec to thwart rogue machines, and at the article's end are links to information about that. Also, understand this particular vulnerability isn't present in 802.1X-protected wireless networks, because the authenticators and supplicants have established authentication and encryption keys that protect individual 802.11 frames.