Executable installers are vulnerable^WEVIL (case 32): Comodo's installers allow arbitrary (remote) code execution WITH escalation of privilege

["Stefan Kanthak" <stefan.kanthak () nexgo de>]

Hi @ll,

the executable installers cispro_30day_installer_1150_8d.exe,
cispremium_installer_6100_08.exe, cav_installer_5951_60.exe,
cav_installer.exe and cfw_installer.exe available from
<http://www.comodo.com> load and execute several DLLs from
their "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>,
<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 these DLLs in the users "Downloads"
directory (for example per drive-by download or social engineering)
this vulnerability becomes a remote code execution.

Due to the application manifest embedded in the executables which
specifies "requireAdministrator" the executable installer is run
with administrative privileges ("protected" administrators are
prompted for consent, unprivileged standard users are prompted for
an administrator password); execution of the DLLs therefore results
in an escalation of privilege!


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

1. visit <http://home.arcor.de/skanthak/sentinel.html>, download
   <http://home.arcor.de/skanthak/download/SENTINEL.DLL> and save
   it as UXTheme.dll in your "Downloads" directory, then copy it
   as DWMAPI.dll, RichEd20.dll, ClbCatQ.dll and ProfAPI.dll;

2. download any of the executable installers provided by Comodo
   and save them in your "Downloads" directory;

3. run the executable installers from the "Downloads" directory;

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

PWNED!


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


stay tuned
Stefan Kanthak


PS: I really LOVE (security) software with such trivial beginner's
    errors. It's a tell-tale sign to better stay away from it!


Timeline:
~~~~~~~~~

2016-01-21    sent report to vendor

              NO ANSWER, not even an acknowledgement of receipt

2016-01-28    resent report to vendor

2016-01-28    Vendor acknowledges receipt

2016-02-29    Vendor informs:
              "update ready, schedule for release during the week of
               March 14"

2016-03-22    Vendor releases updates; see the release notes
              <https://cdn.download.comodo.com/cis/download/installs/updates/release/inis_4055/release_notes.html>

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