BugTraq
Defense in depth -- the Microsoft way (part 8): execute everywhere! Aug 24 2013 09:32PM
Stefan Kanthak (stefan kanthak nexgo de) (1 replies)
Re: [Full-disclosure] Defense in depth -- the Microsoft way (part 8): execute everywhere! Aug 24 2013 10:33PM
Jeffrey Walton (noloader gmail com) (3 replies)
Hi Stefan,

> ... administrative rights for every user account
Hmmm... XP/x64 appears to have a bug such that the second user also
needs to be admin (perhaps XP/x86, too). XP does not recognize the
first account as admin, so the second account cannot be limited (at
least on my test box).

Vista and above make the first user admin, but others users default to standard.

Jeff

On Sat, Aug 24, 2013 at 5:32 PM, Stefan Kanthak <stefan.kanthak (at) nexgo (dot) de [email concealed]> wrote:
> Hi,
>
> since it's start about 20 years ago Windows NT supports (fine grained)
> ACLs, including the permission "execute file".
>
> In their very finite wisdom Microsoft but decided back then to have
> this permission set on EVERY file a user creates (and assumes it is
> set on local and remote file systems which dont support ACLs).
>
> The result: on Windows, malware can run everywhere (and since CWD
> alias "." is in the path, can be started everywhere)!
>
>
> These fundamental errors, combined with two other fundamental errors
> (NO ACLs on %SystemRoot% and %ProgramFiles% to prevent write access
> for non-administrative user accounts, and administrative rights for
> every user account) turned Windows NT into the same unsafe, insecure
> and vulnerable system its predecessors MS-DOS and Windows 3.x were
> and enabled miscreants to abuse internet-connected Windows systems
> to distribute SPAM, launch DDoS attacks, spread malware, etc.
>
>
> For a company that puts "compatibility" above all other criteria this
> decision might have looked reasonable ... BUT: it was NOT!
>
>
> Windows NT introduced the Win32-API, which is/was INCOMPATIBLE to the
> existing DOS- and Win16-API. To run existing applications written for
> the old APIs Windows NT introduced NTVDM (the "Virtual DOS Machine")
> and WoW (the "Windows on Windows" subsystem); only these Windows NT
> components had to be made compatible (and "unsafe" enough to run old
> applications).
>
> There was ABSOLUTELY no need to sacrifice the safety and security of
> Windows NT and the Win32-API for the sake of "compatibility": the
> Win32-API was new, no existing applications had to be supported!
>
>
> Then sloppy developers started to build their applications for the
> Win32-API of this unsafe/insecure environment ... and expected their
> unsuspecting victims^Wusers to have write access to %SystemRoot% and/or
> %ProgramFiles% to write their *.INI files, for example, or to run their
> crapware with administrative or power-user rights.
>
>
> JFTR: since many years Microsoft makes many (almost futile) attempts
> to mitigate the effect of their wrong design decision(s), for example:
>
> * <http://support.microsoft.com/kb/269049> alias
> <http://technet.microsoft.com/security/bulletin/ms00-052>
>
> * <http://support.microsoft.com/kb/306850>
>
> * <http://support.microsoft.com/kb/905890>
>
> * <http://support.microsoft.com/kb/953818> alias
> <http://technet.microsoft.com/security/advisory/953818>
>
> * <http://support.microsoft.com/kb/959426> alias
> <http://technet.microsoft.com/security/bulletin/ms09-015>
>
> * <http://support.microsoft.com/kb/2264107>
>
> * <http://support.microsoft.com/kb/2269637> alias
> <http://technet.microsoft.com/security/advisory/2269637> PLUS the
> 28(!) security bulletins listed there
>
> but NEVER tackled the source of the problem!
>
>
> Instead they introduced things like the "security theatre" UAC: with
> Windows 8 the user account(s) created during setup still have
> administrative rights. And Windows 7 introduced the "silent" elevation
> for about 70 of Microsoft own programs...
>
>
> stay tuned
> Stefan Kanthak
>
>
> PS: if you want to mitigate the wrong design decision that every file
> is "executable": add and propagate an inheritable-only "deny" ACE
> with "execute file" permission for the user group "WORLD\Everyone"
> alias "S-1-1-0", "(D;OIIO;WP;;;WD)" in SDDL notation, at least for
> "%USERPROFILE%" and "%ALLUSERSPROFILE%" alias "%ProgramData%".
>
> On Windows NT 6.x, consider to add another "deny" ACE which prevents
> the directories/objects owner from changing/removing that permission:
> "(D;;WDAC;;;OW)" in SDDL notation.
>
> Since this mitigation will stop "Administrators" and "LocalSystem"
> to run files in their user profiles (to be precise: in "%TEMP%"
> alias "%USERPROFILE%\Local Settings\Application Data\TEMP" resp.
> "%USERPROFILE%\AppData\TEMP" where self-extracting installers will
> typically unpack and execute their payload) you'll have to remove
> the user environment variables TEMP and TMP of these user accounts
> (setting the system environment variables TEMP and TMP which point
> to %SystemRoot%\TEMP into effect).
>
>
> See the script <http://home.arcor.de/skanthak/download/~EXECUTE.INF>
> for a POC (targetting Windows NT 5.x). It sets the "deny" ACE also
> on subordinate directories which are exempt from ACL inheritance,
> as well as some of the user-writable subdirectories of %SystemRoot%
> which dont host executable files.
>
> WARNING: unfortunately the (only) Microsoft utility which allows to
> add the specific ACEs, ICACLS.EXE, used in this script has but a
> serious bug; cf. <http://seclists.org/fulldisclosure/2012/May/109>

[ reply ]
Re: [Full-disclosure] Defense in depth -- the Microsoft way (part 8): execute everywhere! Aug 26 2013 03:16PM
James Lay (jlay slave-tothe-box net) (1 replies)
Re: [Full-disclosure] Defense in depth -- the Microsoft way (part 8): execute everywhere! Aug 25 2013 12:07AM
Stefan Kanthak (stefan kanthak nexgo de)


 

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