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Re: Microsoft Security Advisory MS 03-007

From: Douglas R. Wilson <dallendoug(at)dallenhome.org>
Date: Mon Mar 17 2003 - 23:17:11 EST

some additional notes from emails I have recieved --

-=-=-=-=-=-=-=-=-

> Douglas,

I must admit, I don't want to be scaremongerish. One published article that is low on details is at
http://www.iss.net/issEn/delivery/xforce/alertdetail.jsp?oid=22029

"It is possible for remote attackers to run arbitrary code on vulnerable Web servers. This vulnerability is currently being exploited in the wild, and X-Force has verified the existence of a functional exploit tool. This vulnerability is in itself very serious, but the existence of robust exploits in the wild dictates that fixes or temporary workarounds should be applied immediately."

I also have some internal/proprietary information that I can't discuss that makes me believe similar.
I will also admit that I have not seen firsthand evidence of a working compromise yet.

> On Mon, 2003-03-17 at 16:02, Douglas R. Wilson wrote:
> > The following test can be used:

Do you need help?X

What I meant was as follows --

the normal path of the exploit would be (very approximated -- I'm guessing here)

  • Anonymous request to webdav provider (httpext.dll)
  • permissions are checked on httpext.dll to see if Anonymous request using Anonymous context can be proccessed
  • internal request from httpext.dll to ntdll.dll (somewhere in the processing)
  • ntdll.dll has buffer overflow condition

On a server that has been "locked down," because the anonymous request doesn't have permission to execute a call to the httpext.dll, the process is stopped.

However, if you are using basic and/or NT authentication, the web request is in the context of the user. so, the process would then be:

  • User request to webdav provider (httpext.dll)
  • permissions are checked on httpext.dll to see if User request using User context can be proccessed
  • internal request from httpext.dll to ntdll.dll (somewhere in the processing)
  • ntdll.dll has buffer overflow condition

Please note that in the second instance, the second step doesn't stop the process if anonymous user permissions are removed. The request would go through, and if it carried the exploit, compromise could occur. I wasn't envisioning a switch in context -- the person would be doing the exploit in the context of the user directly in the exception I envisioned. (i.e., a user logs into a website, and then, while logged in, feeds the overflow (or, more likely, a compromised account is used to do this to get around the lockout on anonymous)

-=-=-=-=-=-=-=-

I appreciate the comments so far! keep them coming!

Thanks,

Do you need more help?X

Doug 

--

Douglas R. Wilson

dallendoug@dallenhome.org

--

"the biologist will tell you that progress is the result of
mutations. mutations are another word for freaks. for god's
sake let's have a little more freakish behavior- not less .
. .
Maybe 90 per cent of the freaks will just be freaks,
ludicrous and pathetic and getting nowhere but into
trouble. . .
Eliminate them, however- bully them into conformity- and
nobody in america will ever be really young any more and
we'll be left standing in the dead center of nowhere."

-- Tennessee Williams


----- Original Message -----
From: "Douglas R. Wilson" 
To: "Focus-MS" 
Sent: Monday, March 17, 2003 5:02 PM
Subject: Microsoft Security Advisory MS 03-007


I developed this for my work environment -- however, I
believe that it isn't proprietary, and am forwarding it to
the list for comment and/or informative values. Hopefully
there are no glaring errors.

Please realize that any information contained in here
should be verified and tested independently before you
apply the process to any environment you are responsible
for. I take no responsibilty for any modifications anyone
makes to their system based on what I put down here.

--

I have done some research today, as many people have asked
the "are my web servers vulnerable/need to be patched, et
al" question in response to the latest MSFT advisory (MS
03-007). It's likely that most servers that can be patched
should be, BUT only after testing, as this may be a much
more impactual problem than first realized, as well as all
the other innate problems inherent with rolling patches out
on production systems.



Microsoft has handled this somewhat differently than a
standard bulletin, and the conjecture on that could easily

Can we help you?X

be a separate discussion. Initially, however, it points to
the fact that this vulnerability is with ALL Windows 2000
servers, period, and they have come out with this patch at
this time because IIS servers are actively being
compromised already, before the bulletin was released, to
deal with an active attack vector. This implies that they
may have rushed the patch out the door, and that the
problems may involve a lot more parts of windows . . .

Points to consider:

·         This may not be something that is an immediate
threat to a lot of the servers if you only consider the IIS
attack vector, if they have been deployed with the IIS
lockdown tool in most configurations. CERTAIN
CONFIGURATIONS OF THE IIS LOCKDOWN TOOL DO LEAVE WEBDAV
ENABLED -- other methods should be employed there. There is
a list of these profiles that I have found at the end of
this.

·         The servers in question may have other things
impacted by the patch, as a core system dll is what is
being replaced by this hotfix.

·         The servers in question may not be able to be
rebooted right away in keeping with SLA?s/production
schedules.



This is an issue with a core dll, ntdll.dll, which (I
believe) is currently being addressed because an exploit
exists that can be injected using IIS as its attack vector.

MSFT recommends the IIS lockdown tool as one specific
solution. However, some people are not sure they have
applied the tool properly, and some people have made
modifications and/or installed other applications since
then (like Cold Fusion) that may add/modify application
mappings, and thus change settings done by the IISLockdown
tool.

I have derived one result from my research as a way to
detect one form of "protection" from the exploit. This only

Can't find what you're looking for?X

addresses nailing down the IIS based attack vector, and
only on certain boxes. However, the only true way to know
for sure is if you have the exploit tool, and try using it,
and it fails.


WebDAV requests are processed in the httpext.dll. This is
NOT the dll that the buffer overflow exists in, but it is
the dll that initially would handle WebDAV requests, and it
is that dll which the IISLockdown tool "locks down."


So, if a windows 2000 server is running IIS 5.0, and it has
had either:

·         Service Pack 3 for windows 2000 installed, or

·         Service Pack 2 and MS02-018: April 2002
Cumulative Patch for Internet Information Services
installed, or later cumulative patches installed,



The following test can be used:


If the C:\winnt\system32\inetsrv\httpext.dll file has ACL?s
on it such that anonymous web context accounts cannot
execute it, the server in question is very likely not
vulnerable to this exploit. (Obviously, if you start
considering the concept of NT Authentication, and various
user accounts accessing the httpext.dll, the scope varies).



Older versions of the lockdown tool will simply deny the
Everyone Group?s permissions to execute -? as long as the
anonymous users haven?t been put in any privileged group,
this is fine. Newer versions of the lockdown tool will
create specific groups for web users, and then specifically
deny permissions on these files.



The reason the service pack level is important is before
MS02-018, some WebDAV requests could get around the
httpext.dll, due to another issue, which is patched in
either MS02-018 or SP3.



There may be some way of scripting up a tool that will
check for the above parameters on servers, to do quick spot
checking, if someone has not already developed a
vulnerability testing tool. As I said before, however, the
only true way to make sure is to attempt the exploit, and

Don't know where to look next?X

have it fail.

IIS Lockdown 2.1 Profiles that leave WebDAV enabled:

Small Business Server 2000
Exchange 2000 (OWA, PF, IM, SMTP, NNTP)
Share Point Portal Server
BizTalk Server 2000
Commerce Server 2000


Initial public release as pertains to Windows 2000:
http://www.microsoft.com/security/security_bulletins/ms03-007.asp



The full bulletin, as pertains to IIS:
http://www.microsoft.com/technet/treeview/?url=/technet/security/bulletin/MS
03-007.asp



Article on WebDAV getting around httpext.dll in earlier
versions:
http://support.microsoft.com/default.aspx?scid=kb%3Ben-us%3B307934



IIS Lockdown Tool 2.1
http://download.microsoft.com/download/iis50/Utility/2.1/NT45XP/EN-US/iisloc
kd.exe

--

Douglas R. Wilson

dallendoug@dallenhome.org

--

"the biologist will tell you that progress is the result of
mutations. mutations are another word for freaks. for god's
sake let's have a little more freakish behavior- not less .
. .
Maybe 90 per cent of the freaks will just be freaks,
ludicrous and pathetic and getting nowhere but into
trouble. . .
Eliminate them, however- bully them into conformity- and
nobody in america will ever be really young any more and
we'll be left standing in the dead center of nowhere."

-- Tennessee Williams

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----------------------------------------------------------------------
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Received on Tue Mar 18 09:38:54 2003

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