%windir%\temp\sso\ssoexec.dll (or: how trustworthy is Microsoft's build process)

["Stefan Kanthak" <stefan.kanthak@xxxxxxxx>]

Hi @ll,

the system image "\Setup\WIM\setup.wim" on the "POSReady 2009 eval CD",
available from the Microsoft Download Center under
<http://www.microsoft.com/downloads/en/details.aspx?FamilyID=1e077ece-3f19-4c41-b219-6fcc821fb5fc>,
contains the following registry entries:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows 
NT\CurrentVersion\Winlogon\Notify\SSOExec]
"Asynchronous"=dword:00000001
"Impersonate"=dword:00000001
"Logoff"="SSOReset"
"Unlock"="SSOExec"
"Lock"="SSOReset"
"DLLName"="%windir%\\temp\\sso\\ssoexec.dll"


The directory "%windir%\temp" in the system image is but empty.


The presence of these registry entries is evidence that (one of) the
system(s) used to build and capture the POSReady 2009 evaluation system
image were infested with malware, and that either the infestation was not
detected at all (bad) or the infestation was detected, but incompletely
(or accidentially, when "%windir%\temp" was cleared) "removed" and a
compromised system used to build the system image (worse).

JFTR: MSFT initiated their "trustworthy computing" about 10 years ago!


To complete the picture: the ACLs on the directory "%windir%\temp" in
systems installed from this image/CD allow unprivileged users to create
a subdirectory "sso" in "%windir%\temp" and then the "ssoexec.dll",
allowing them to have their code run under every (other) user account
used to log on afterwards, resulting in a privilege escalation.


Timeline
~~~~~~~~

2012-02-03    informed vendor

2012-02-03    vendor replies:
              "The registry key and DLL are part of the Windows embedded
               software package and their existence is expected."

.oO(OUCH! they must be joking...)

2012-02-04    informed vendor that SSOEXEC.DLL is NOT part of any Windows
              software package

2012-02-06    vendor replies:
              "we are still looking and hope to provide clarification soon."

2012-02-06    vendor replies:
              "this reference in no way indicates there is or ever was a
               virus on our build systems."

2012-02-08    asked vendor to consider that both
              <http://www.bing.com/search?q=ssoexec> and
              
<https://encrypted.google.com/search?num=100&safe=off&q=%22ssoexec%22+OR+%22ssoreset%22>
              only find hits that show problems with malware

2012-03-04    no more answer from vendor, report published


Stefan Kanthak