Microsoft Bypasses HOSTS File

whitehatlurker writes "Dave Korn announced on the Full Disclosure and Bugtraq security lists that Microsoft is bypassing local lookups for some hosts, meaning that you can't locally block some sites through your HOSTS file. All of these sites are MicroSoft controlled sites. The general feeling in the rest of the thread is that this was to obfuscate these hosts and prevent them from being blocked by malware. However, there are no non-MicroSoft hosts listed, giving a competitive advantage for MicroSoft's anti-malware tools over other brands."

Not a useful thing for MS to do

I would have thought that if you cant subvert the HOSTS file then all you have to do is to intercept any DNS lookup of these MS addresses and you would have the same effect.

If you are trying to stop MS software from talking to home, then just use an external firewall.

Michael

I couldn't reproduce this on Win2K.

I'm wondering if the behaviour will change if you just go into "services" and disable the DNS client.

I recommend this anyway. In theory it will increase the number of requests your machine does. But in practice it has saved me a lot of "try rebooting" calls.

Anyone out there with XP who can reproduce this?

Re:I couldn't reproduce this on Win2K.

Anyone out there with XP who can reproduce this?

Good idea, but no luck. Same result, though with one slight difference which might prove useful as a workaround - The first attempt timed out, meaning it really performs the query rather than having a hardcoded list of IP mappings. So if you ran a cacheing DNS proxy on your machine (ie, exactly what the built-in DNS service does, but one not containing a built-in Microsoft hack), pointed your machine's DNS to itself, and tell the proxy to use a bogus address for the sites in question, that should successfully block them.

Better to do this at the firewall, though (a real external hardware firewall, not Microsoft's "trust us, this works" crap).

Re:Not a useful thing for MS to do

What is there to stop a virus making edits to the dll binary? Changing the strings that presently correspond to the IP addresses of MS domains to some random, invalid address?

Re:Not a useful thing for MS to do

>What is there to stop a virus making edits to the dll binary? Changing the strings that presently
>correspond to the IP addresses of MS domains to some random, invalid address?

Yes, there is a mechanism built into Windows which uses digital signatures and a watchdog to prevent accidental (or deliberate) changes to sensitive DLLs. Any binary changes to any file will invalidate the signature on the DLL. This is more effective than tripwire or other such things whereby a checksum is held in another location since the DLL itself is signed using a PK and cannot be re-signed to hide the changes.

Windows File Protection: http://support.microsoft.com/?kbid=222193 [microsoft.com]

- Oisin

Is this necessarily a bad thing?

It helps prevent Malware. Sure, MS might have a slim advantage, but it also prevents otherwise botted PCs from accessing MS Updates against things like Blaster. I don't see this as being such a big deal.

It's a Big Deal because...

As mentioned in TFA's thread:

2) As far as I know, their malicious software removal tool didn't exist back when this behavior was created, so what good was keeping access to Microsoft open going to do an infected system? What good does it do to install a patch for a vulnerability that's already been exploited onto the computer of the archetypal "home user"?

MS hardcoded this in with WinXP SP2 & Win2k3 SP1.

Why? Maybe someone will get a comment from MS.

The point is that mucking around with the inner workings of the OS is BAD, unless it is documented appropriately. Now, documentation doesn't make it good, but if they're departing from the expected behavior, they should let people know.

Re:Is this necessarily a bad thing?

I agree. In addition, as much as I may think they should include other sites on that list, those other sites do not play into what MicroSoft sees as the "integrity" of their product. They're not out to make sure that you can get the latest update of Apache or OpenOffice or whatever; they want to make sure that you can update Windows to the latest version (one that might actually stop the malware they're trying to protect from) or get to a place where you can ask MicroSoft a question (which they may or may not answer, and if they do, the answer to which may or may not be helpful), or, heaven forbid, get to a place where you can order a new MicroSoft product (probably because you haven't realized it will have similar flaws to your current and older MS products).

Re:Is this necessarily a bad thing?

> I didn't even know about the hosts file until 5 minutes ago

and already you feel qualified to comment

Re:Is this necessarily a bad thing?

Absolutely, yes, it is a bad thing.

Microsoft has:
        instituted not only License 6, but also "phone home" validation. At any time, MS may
        decide to shut down any business worldwide that uses their products, at their (or a
        malviolent government's) discretion;

        embraced and extended(tm) LDAP with kerberos authentication that is not industry-
        standard or cross-platform compatible;

        embraced and extended(tm) web browser standards that have made Internet and
        platform security a nightmare;

        implimented a software firewall (XP SP2) that doesn't actually control/restrict all
        incoming and outgoing packets, making the use of a third party (H/W?) firewall
        less redundant and more actually necessary;

        stripped nearly all OS improvements out of their upcoming flagship OS, excepting
        Digital Rights Restrictions -- which may also remotely disable or remove products
        and/or services which they choose to disallow for any reason.

Bypassing DNS and the hosts file on the OS platform is their "camel's nose under the
tent flap" for future modifications to the network stack, all in the name of their brand
of "security", which is (frankly) appalling. Given Microsoft's current product direction,
it is not outside the realm of possibility that the future average computer user's
experience will be some cross between a WebTV and an XBox.

So what?

People should know by now, when you go MS, you don't buy the horse, you buy the farm. You wanna segment and pick and choose on the MS platform? Good luck.

Re:So what?

No, no... You just *license* the farm. MS still owns it. For a nominal fee, they'll let you step in the cow pies every second Tuesday.

Ad blocking

Microsoft could also be using this to prevent users from blocking MSN messenger ad servers.

Permissions?

tom@localhost ~ $ ls -l /etc/hosts
-rw-r--r-- 1 root root 519 Oct 19 12:13 /etc/hosts

....

Why can't windows just make the host files read only.

Re:Permissions?

Yes, but the motivation to ignore the hosts file is because of viruses that could overwrite it.

So ... if a user level virus couldn't write to the host file ...

Think about it.

Tom

Re:Permissions?

So ... if a user level virus couldn't write to the host file ...

Which leads us back to the primordial Windows security problem: users running with admin priviledges.

In the example you provided in the previous post, /etc/hosts is writable only by root. If user runs as root all the time, then it's back to square one.

As far as I know Windows host file is only writable by Administrator level (dunno, I don't have a Windows machine with me right now). Is it otherwise?

Re:Permissions?

On Windows Server 2003 SP1:

C:\WINNT\system32\drivers\etc\hosts
BUILTIN\Users :R
BUILTIN\Power Users:R
BUILTIN\Administrators:F
NT AUTHORITY\SYSTEM:F

Normal and power users get read, Administrators and SYSTEM get full control, all inherited from the drivers directory.

You're absolutely right about the root problem as running everything as admin. Almost all the malware that I've seen fails miserably unless run as admin, and that which does run can't infect the entire system. I guess the users that know enough to run as a normal user are the same ones that avoid that crap in the first place.

Re:Permissions?

So ... if a user level virus couldn't write to the host file ...

Think about it.

Dear Tom,
this is Slashdot and the term "think" does not apply.

Re:Permissions?

Windows security is as effective as a screen door on a submarine.

It'd take the malware makers about an hour to find any of the what, probably 80 holes that would let them go around such windows security. A back-and-forth battle like that could easily go on for months if not years. In unix, security and permissions are the foundation, on top of which everything is built. In windows, security is a hack that was added on later with no due consideration during the initial design phase of windows. It's no wonder it's next to impossible to get it to work the way you want it to.

When you are designing security, the sad truth of it is, the user is the enemy. There's no nicer way to look at it. So it takes a great deal of care to design a security system that can withstand the assult of a user while at the same time being functional and serving the user. It's too late for windows to make those design considerations. They have errored on the side of functionality and sacrificed the security of the system. There is no fixing that.

Re:Permissions?

funny, I see write access by root there. And last I checked, when malware *owns* windows, it's local root, which means the permissions you speak of would amount to absolutely nothing... And btw, you can make it read only to normal users, but again, this would accomplish nothing.

conspiracy-theorists, start your engines!

Well, lucky I've got that brand new tinfoil-hat!

Potentially unfair...

The main problem is not that you can't block MS addresses, it is that MS is only preventing their addresses from being blocked. Since they are now getting into the security business, this gives them what could be seen as an unfair advantage.

Let us say that Joe User gets a piece of Malware, so he decides to visit a security company to find a solution to his problem. However, the malware has modified his hosts file to block security company web pages from being accessed, which is extremely typical. Joe User is not experienced enough to even know there is a hosts file that he could change back.

Joe User's first attempt would likely be to norton.com, symantec.com (both go to Symantec's main page), or mcafee.com, since these names are pretty much synonymous with antivirus software. However, all of those are blocked and he can't access them.

However, if he goes to microsoft.com, he can go there since the hosts file is subverted in the OS. Since he can't spend the time to figure out why he can't access the others, he purchases Microsoft's AV solution.

Yet Another Band-Aid?

Hmm. This seems a bit ass-backwards to me.

Rather than having to ignore the HOSTS file because it may be malicious, shouldn't the solution be to prevent HOSTS from getting mangled in the first place?

(oh, and on an unrelated note: why on earth is the Win32 HOSTS file buried away under C:\Windows\System32\Drivers\etc\? I mean.... 'drivers'?!!? Bizarre.

Re:Yet Another Band-Aid?

The solution exists. Running as standard user in Windows XP will prevent changes to the hosts file.

Re:Yet Another Band-Aid?

I've always found the /etc/ to be the funniest part of that path.

This is one of the telltale remaints of the BSD-derived [kuro5hin.org] TCP/IP stack that NT/XP uses.

Although the stack itself has been heavily modified, using /etc/ as the location for the hosts file still remains, along with other little hints -- ftp.exe is almost identical to the BSD FTP utility. BSD also gets properly credited in the XP copyright notice [microsoft.com]

MSN

The only thing that troubles me is the inclusion of MSN.com in the list.

The other hosts are used in Microsoft's patch distribution network and honestly is not something the average user would ever need to block. It is, however, something a virus/spyware program would love to block. So, if you want to block those hosts, buy a firewall, they're down to about $20.

As for MSN, my only guess is that they don't want to block updates for MSN messenger.

What we have to remember is that these sites are required to fix a broken system, so I don't view this as just an advantage for MS antispyware.

How is this a competitive advantage?

so...how is this a competitive advantage? why can't the competitors just use IP addresses instead of DNS?

Smart move from M$

How long before somebody poisons these adresses in the DNS servers ?

An automatic update of WMP and your PC gets owned, and nothing can be done to prevent it!

Would be ok...

...if Microsoft had documented this behavior. Yet still, I fail to see what the big deal is. So you can't force an IP address to a domain with hosts.txt for some sites that microsoft controls. If you need to do that, for example for some corporate filter or updating solution, you could just modify your own dns server. Home users on the other hand get more reliable access to windows update, which is very important. Otherwise it would be trivial for malware to block the computer from recieving updates, and the automatic updates would silently fail.

Cheers, Fogger

Route to null

If the adware can change your hosts file then this is pretty useless anyway. Now all the software has to do is run a script that does the following

nslookup whatever.microsofts.domains
takes the list of return addresses and
route ADD destination MASK mask INVALID INVALID INVALID foreach

and your traffic to MS wont even leave the network card.

Interference with my sig!

How nasty of MS to interfere with my sig!
Now I'll have to include a disclaimer...

Just another reason to continue using a more robust system :)

Sensationalism

Who cares?

Nothing prevents you from not using the operating system's resolver. Its trivial to implement your OWN DNS client in your programs, bypassing any HOSTS settings and other DNS resolver issues.

I've never seen so many people who were so clueless and misinformed about the technical issues involved here.

Sensationalist Junk

If they removed other sites from the host file then there would be an article on Slashdot about how XYZ site can't be blocked in the host file and about how that is some nefarious evil plot by Microsoft. Microsoft did just what they should logically do: Removed their own sites from host lookups.

The problems with this

The real problem with this is that: 1. It wasn't documented, so people had to discover this non-intuitive exception. 2. It defeats the purpose of the hosts file. Had they also included the other AV vendors in the list and made the function public it may have seemed like a practical band aid to the hosts file hijacking problem. Instead they made it M$ only and hid it so it looks slimy. The issue is being addressed is also PEBKAC related.. If Windows users weren't logged in as admin the hosts file would be off limits.

Hotels on Park Place

How come the Department of Justice, supposedly "closely monitoring" Microsoft's monopoly abuse, isn't stopping this? How come Microsoft isn't afraid to pull this Internet bundling stunt, illegally leveraging its monopoly, after the "landmark decision" against them 6 years ago?