Hi @ll,

the executable installer QNAPQsyncClientWindows-4.2.1.0602.exe,
available from <https://www.qnap.com/en/download>, has (like
almost all executable installers) multiple vulnerabilities:


#1: arbitrary (remote) code execution WITH escalation of privilege
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On a fully patched Windows 7 SP1 it loads and executes the following
Windows system DLLs from its "application directory" instead the
"system directory" %SystemRoot%\System32\:
    Version.dll, UXTheme.dll, WinMM.dll, SAMCli.dll, MSACM32.dll,
    SFC.dll, SFC_OS.dll, DWMAPI.dll, MPR.dll, ShFolder.dll,
    NTMARTA.dll

On other versions of Windows this list changes, but the vulnerable
executable installer always loads and executes some DLLs from its
"application directory".

This weakness is well-known and well-documented:
see <https://cwe.mitre.org/data/definitions/426.html>
and <https://cwe.mitre.org/data/definitions/427.html>
plus <https://capec.mitre.org/data/definitions/471.html>.

See <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> for
mitigations of this beginner's error.

For software downloaded with a web browser the "application
directory" is typically the user's "Downloads" directory: see
<https://insights.sei.cmu.edu/cert/2008/09/carpet-bombing-and-directory-poisoning.html>,
<http://blog.acrossecurity.com/2012/02/downloads-folder-binary-planting.html>
and <http://seclists.org/fulldisclosure/2012/Aug/134>

If an attacker places one of the DLLs named above in the users
"Downloads" directory (for example per drive-by download, social
engineering, ...) this vulnerability becomes a remote code
execution WITH escalation of privilege.

Thanks to its "installer detection" Windows' user account control
requests administrative rights for the executable installer, the
DLLs entry points are called with administrative rights -> PWNED!

Demonstration:

1. download <http://home.arcor.de/skanthak/download/SENTINEL.DLL>
   and save it as Version.dll in your "Downloads" directory, then
   copy it as UXTheme.dll and NTMARTA.dll there too;

2. download
   <https://eu1.qnap.com/Storage/Utility/QNAPQsyncClientWindows-4.2.1.0602.exe>
   and save it your "Downloads" directory;

3. execute QNAPQsyncClientWindows-4.2.1.0602.exe from your
   "Downloads" directory;

4. notice the message boxes displayed from ShFolder.dll etc. placed
   in step 1.


#2: unsafe %TEMP% directory
~~~~~~~~~~~~~~~~~~~~~~~~~~~

It creates a subdirectory ns<letter><random_hex_value>.tmp in %TEMP%
where it extracts multiple DLLs to and executes them.
This subdirectory inherits the access rights of its parent %TEMP%,
so an unprivileged attacker^Wuser can replace the DLLs between their
creation and execution, again resulting in arbitrary code execution
with escalation of privilege.

See <https://cwe.mitre.org/data/definitions/377.html> and
<https://cwe.mitre.org/data/definitions/379.html> for this
well-known and well-documented weakness.

Demonstration:

create the following batch script

:WAIT
@If Not Exist "%TEMP%\ns*.tmp" Goto :WAIT
For /D %%! In ("%TEMP%\ns*.tmp") Do Set foobar=%%!
For %%! In ("%foobar%\*.dll") Do Copy /Y "%USERPROFILE%\Downloads\Version.dll" "%%!"

and start it, then rerun QNAPQsyncClientWindows-4.2.1.0602.exe


Additionally see <http://seclists.org/fulldisclosure/2015/Dec/32>,
<http://seclists.org/fulldisclosure/2015/Oct/109>,
<http://seclists.org/fulldisclosure/2015/Nov/101> and
<http://seclists.org/fulldisclosure/2015/Dec/86>,
plus <https://skanthak.homepage.t-online.de/!execute.html>
and <https://skanthak.homepage.t-online.de/sentinel.html>


FIX:
~~~~

* DON'T build executable installers at all!

* Provide either a *.MSI or a *.CAB plus an *.INF

* NEVER use executable installers at all!

* Add the NTFS ACE "(D;OIIO;WP;;;WD)" meaning
  "deny execution of files in this directory and all subdirectories"
  to the NTFS ACL of every %TEMP% directory!

  JFTR: when execution in %TEMP% is denied, the defective
        installer display a dialog box with the blatant lie

        "QSync is running.
         Click [OK] to close QSync and continue the installation,
         or [Cancel] to terminate the process."

        and repeats it after clicking [OK], over and over again.
        The only way to exit this loop is [Cancel]


stay tuned
Stefan Kanthak


Timeline:
~~~~~~~~~

2017-07-29    vulnerability report sent to vendor

              automated response from vendor:
              "Our team will get back to you as soon as possible."

              no more reaction from vendor

2017-08-07    vulnerability report resent to vendor

              automated response from vendor:
              "Our team will get back to you as soon as possible."

              no more reaction from vendor
            
2017-08-16    report published