Hi,

putty-0.66-installer.exe loads and executes DWMAPI.dll or
UXTheme.dll from its "application directory".


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>,
<https://blog.acrossecurity.com/2012/02/downloads-folder-binary-planting.html>
and <https://seclists.org/fulldisclosure/2012/Aug/134> for
"prior art" about this well-known and well-documented vulnerability.


If an attacker places one of the above named DLL in the user's
"Downloads" directory (for example per "drive-by download"
or "social engineering") this vulnerability becomes a remote
code execution.


Proof of concept/demonstration:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1. visit <https://home.arcor.de/skanthak/sentinel.html>, download
   <https://home.arcor.de/skanthak/download/SENTINEL.DLL>, save it
   as UXTheme.dll in your "Downloads" directory, then copy it as
   DWMAPI.dll;

2. download putty-0.66-installer.exe and save it in your
   "Downloads" directory;

3. execute putty-0.66-installer.exe from your "Downloads"
   directory;

4. notice the message boxes displayed from the DLLs placed in
   step 1.

PWNED!


See <https://seclists.org/fulldisclosure/2015/Nov/101>,
<https://seclists.org/fulldisclosure/2015/Dec/86> and
<https://seclists.org/fulldisclosure/2015/Dec/32> plus
<https://home.arcor.de/skanthak/!execute.html> and
<https://home.arcor.de/skanthak/sentinel.html> for details about
this well-known and well-documented BEGINNER'S error!  


stay tuned
Stefan Kanthak


Timeline:
~~~~~~~~~

2015-12-24    sent vulnerability report to author

              NO REPLY, not even an acknowledgement of receipt

2016-01-02    resent vulnerability report to author

              NO REPLY, not even an acknowledgement of receipt

2016-03-01    report published