Re: Microsoft Security Advisory MS 03-007

From: Douglas R. Wilson (dallendoug@dallenhome.org)
Date: 03/18/03

  • Next message: Joseph Durnal: "Microsoft Security Advisory MS 03-007 - Problems"
    Date: Mon, 17 Mar 2003 23:17:11 -0500
    From: "Douglas R. Wilson" <dallendoug@dallenhome.org>
    To: Focus-MS <focus-ms@securityfocus.com>
    
    

    some additional notes from emails I have recieved --

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

    > Douglas,
    > You say "IIS servers are actively being compromised already,
    > before the bulletin was released" --- do you have any links to
    > documentation about this? I haven't heard of this.
    >
    > Also, besides IIS, what methods are available to exploit the
    > vulnerability in ntdll.dll ?"

    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:
    > >
    > >
    > > 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).
    >
    > But the MS advisory warns of SYSTEM access if compromised. Doesn't that
    > mean that whatever crashes happens before IIS switches user context?

    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,

    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" <dallendoug@dallenhome.org>
    To: "Focus-MS" <focus-ms@securityfocus.com>
    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
    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
    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
    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
    ----------------------------------------------------------------------
    ALERT: How a Hacker Uses SQL Injection to Steal Your SQL Data!
    It's as simple as placing additional SQL commands into a Web Form input
    box giving hackers complete access to all your backend systems!
    http://www.spidynamics.com/mktg/sqlinjection33
    ----------------------------------------------------------------------
    ALERT: How a Hacker Uses SQL Injection to Steal Your SQL Data!
    It's as simple as placing additional SQL commands into a Web Form input 
    box giving hackers complete access to all your backend systems! 
    http://www.spidynamics.com/mktg/sqlinjection33
    

  • Next message: Joseph Durnal: "Microsoft Security Advisory MS 03-007 - Problems"

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