Hi @ll,

the executable installers "TrueCrypt Setup 7.1a.exe" and
TrueCrypt-7.2.exe load and execute USP10.dll, RichEd20.dll,
NTMarta.dll and SRClient.dll 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> for "prior art"
about this well-known and well-documented vulnerability.


If an attacker places the above named 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 installers are 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:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(verified on Windows XP, Windows Vista, Windows 7, Windows Server
2008 [R2]; should work on newer versions too)

1. visit <http://home.arcor.de/skanthak/sentinel.html>, download
   <http://home.arcor.de/skanthak/download/SENTINEL.DLL> and store
   it as USP10.dll in your "Downloads" directory, then copy it as
   NTMarta.dll, RichEd20.dll and SRClient.dll;

2. download TrueCrypt-7.2.exe and "TrueCrypt Setup 7.1a.exe" and
   store them in your "Downloads" directory;

3. run TrueCrypt-7.2.exe and "TrueCrypt Setup 7.1a.exe" from your
   "Downloads" directory;

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

PWNED!


5. on Windows XP copy the downloaded USP10.dll as SetupAPI.dll (or
   create an empty file SetupAPI.dll), then rerun TrueCrypt*.exe
   from your "Downloads" directory.

DOSSED!


The denial of service from step 5. can easily be turned into an
arbitrary code execution with elevation of privilege too: add the
exports SetupDiOpenClassRegKey, SetupInstallFromInfSectionA,
SetupOpenInfFileA and SetupCloseInfFile to the SetupAPI.dll copied
to the "Downloads" directory.


For this well-known (trivial, easy to avoid, easy to detect and
easy to fix) beginner's error see
<https://capec.mitre.org/data/definitions/471.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>


See <http://seclists.org/fulldisclosure/2015/Nov/101>,
<http://seclists.org/fulldisclosure/2015/Dec/86> and
<http://seclists.org/fulldisclosure/2015/Dec/121> plus
<http://home.arcor.de/skanthak/sentinel.html> and the still unfinished
<http://home.arcor.de/skanthak/!execute.html> for more details and why
executable installers (and self-extractors too) are bad and should be
dumped.


stay tuned
Stefan Kanthak


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


Timeline:
~~~~~~~~~

2015-12-23    report sent to vendor

              NO ANSWER, not even an acknowledgement of receipt

2016-01-01    reports resent to vendor

              NO ANSWER, not even an acknowledgement of receipt

2016-01-08    report published