Message-ID: <4A60200518A14C9387F4741BA6FDC10C@celsius>
Date: Fri, 25 Jul 2014 19:12:48 +0200
From: "Stefan Kanthak" <stefan.kanthak@...go.de>
To: "Gynvael Coldwind" <gynvael@...dwind.pl>
Cc: "fulldisclosure" <fulldisclosure@...lists.org>,
  "Brandon Perry" <bperry.volatile@...il.com>, <bugtraq@...urityfocus.com>
Subject: Re: [FD] Beginner's error: import function of Windows Mail executes rogue program C:\Program.exe with credentials of other account

Gynvael Coldwind wrote:

> So reading the links you provided I semi-agree with you. I think the
> problem boils down to this part of your initial e-mail:
> 
>> PS: yes, it needs administrative privileges to write C:\Program.exe.
>>    BUT: all the user account(s) created during Windows setup have
>>    administrative privileges.
> 
> My point was (and it still stands) that if you have admin access, this
> isn't a privilege escalation, as there is no "escalation" part here.

Correct.
If only Microsoft would educate its users to exercise STRICT user
separation and use different accounts for administration and daily work.

This is where and why UAC chimes in (which answers your question below):
Joe Average uses the administrative account created during Windows setup,
but UAC strips the administrator rights.
Microsoft "sells" UAC as "Joe Average works with standard user rights"
or "Joe Average is not an administrator any more", neglecting that Joe
will happily approve almost every request for administrative rights (or
isnt asked at all when one of the about 70 Windows executables which are
exempt from the elevation prompt are auto-elevated).

> The links you provided use different wording, e.g.
> (http://blogs.technet.com/b/srd/archive/2013/07/09/assessing-risk-for-the-july-2013-security-updates.aspx):
> "To exploit the vulnerability addressed by this update, attacker must
> have permission to create a new file at the root of the system drive.
> (C:\malicious.exe)"
> 
> This makes of course more sense, though as I did mention above, it
> does seem to require deliberate action from the administrator to
> actually allow a non-admin user the WD (add file to directory)
> privilege on C:\, which is rather rare I would say.

Correct.
This argument holds as long as strict user separation is exercised.
But with UAC, Joe Average is both user and administrator, and isnt
really aware of his split personality.

> That being said, after thinking about it again I do see your point,
> which I interpret at: even if an administrator grants all users WD/AD
> on C:\, there should be no reason for him to worry, as there is no
> reason to suspect files placed in C:\ are going to auto-execute on
> certain events*.
> * let's leave autoexec.bat/config.sys out of this, as that branch of
> Windows is long dead and supported only FAT anyway
> 
> So let me change my initial e-mail to: Congratz on finding the bug :)
> 
> (BTW not sure why did you bring UAC into the discussion - did I miss
> something? or was it just an argument you've heard before and wanted
> to reply to it preventively?)
> 
> Cheers!

regards
Stefan


> On Fri, Jul 25, 2014 at 2:50 PM, Stefan Kanthak <stefan.kanthak@...go.de> wrote:
>> Gynvael Coldwind wrote:
>>
>>> Well it was discussed a couple of times recently on FD that this is a bug,
>>> but it's not a privilege escalation.
>>> If you are admin (and you did mention that it's a prerequisite) you can
>>> execute code as other users anyway - so there's no *escalation* here.
>>>
>>> Therefore it's not a security bug (unless you are using a super old version
>>> of Windows with incorrect ACLs on c:\, which sounds like a bug in itself),
>>> just a "normal" bug.
>>> Not sure if FD is the right place for non-security bugs tbh.
>>
>> If these bugs were no security bugs: why does Microsoft then publish fixes
>> for (at least some of) them via MSRC bulletins and Windows Update?
>>
>> See <https://technet.microsoft.com/library/security/ms13-058.aspx>
>> or <https://technet.microsoft.com/library/security/ms13-034.aspx>
>>
>> Or pulls drivers whose setup routines show these bugs from Windows Update?
>>
>> See <http://seclists.org/fulldisclosure/2014/May/40>
>>
>>
>> Also try to see these bugs as a blended threat:
>>
>> * during Windows setup Microsoft still creates all user accounts as
>>   administrators.
>>
>> * Microsoft sells its unsuspecting users UAC as a security feature, but does
>>   NOT inform them (or at least does not inform Joe Average) that UAC is not
>>   a security boundary and they should better use a restricted^Wstandard user
>>   account instead of the administrator account created during setup.
>>
>> * Joe Average will happily give consent to any program which presents an UAC
>>   prompt to him: he wants to get his work done, and this UAC prompt is just
>>   an annoyance. BTW: when Windows asks him for consent, this must be right?
>>
>> regards
>> Stefan
>>
>>> Cheers,
>>> On 25 Jul 2014 00:46, "Stefan Kanthak" <stefan.kanthak@...go.de> wrote:
>>>
>>>> Brandon Perry wrote:
>>>>
>>>> > So, I am very curious how you are finding these? Have you automated this
>>>> or
>>>> > is it manual hand work?
>>>>
>>>> All my Windows installations have
>>>> <http://home.arcor.de/skanthak/download/SENTINEL.EXE> and
>>>> <http://home.arcor.de/skanthak/download/SENTINEL.DLL> preinstalled as
>>>> C:\Program.exe and C:\Program.dll, so I'm notified when some poorly written
>>>> program tries to execute them.
>>>> The sentinels call MessageBox() with "MB_SERVICE_NOTIFICATION", so the
>>>> messages are recorded in the event log too where I can find them later.
>>>>
>>>> I also preinstall an APPINIT.DLL <https://support.microsoft.com/kb/197571>
>>>> which logs all command lines of programs linked to USER32.DLL to a file:
>>>> filtering for "C:\Program " at column 1 lists all the culprits.
>>>>
>>>> My third source is a SAFER.Log <
>>>> https://technet.microsoft.com/cc786941.aspx>
>>>> where every execution attempt is logged, including the executables caller:
>>>> filtering this for "\program.exe" or "\program.dll" lists all the culprits.
>>>>
>>>> So basically I just have to sit and wait...
>>>>
>>>> In case one of my customers was hit, and this did not happen during an
>>>> installation, I have to interrogate them what they did... and hope they can
>>>> remember with sufficient detail.
>>>>
>>>> But almost all hits occur during installations or the customization
>>>> following
>>>> an installation (here it was the import of existing mails into a new
>>>> account),
>>>> so these are not so difficult to reproduce.
>>>>
>>>> regards
>>>> Stefan
>>>>
>>>> PS: of course it helps if 8.3 names are disabled and "C:\Program Files\"
>>>> can't
>>>>     be aliased as C:\Progra~1\
>>>>     To achieve this just run FORMAT C: /FS:NTFS /S:Disable in Windows PE
>>>>     before you start the installation of Windows 7 and later.
>>>>     For Windows NT5.x you'll have to use \i386\MIGRATE.INF
>>>>
>>>> > On Wed, Jul 23, 2014 at 2:50 PM, Stefan Kanthak <stefan.kanthak@...go.de
>>>> >
>>>> > wrote:
>>>> >
>>>> >> Hi @ll,
>>>> >>
>>>> >> the import function of Windows Mail executes a rogue program
>>>> C:\Program.exe
>>>> >> with the credentials of another account, resulting in a privilege
>>>> >> escalation!
>>>>
>>>> [...]
>>>>
>>>> _______________________________________________
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>>>>
>>>
> 
> 
> 
> -- 
> Gynvael Coldwind

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