Date: Mon, 21 Dec 2015 12:13:31 +0100
From: "Stefan Kanthak" <stefan.kanthak@...go.de>
To: <fulldisclosure@...lists.org>
Cc: bugtraq@...urityfocus.com
Subject: [FD] Executable installers are vulnerable^WEVIL (case 13): ESET
	NOD32 antivirus installer allows remote code execution with
	escalation of privilege

Hi @ll,

the executable installer [°] of ESET's NOD32 antivirus,
eset_nod32_antivirus_live_installer_.exe, loads and executes
(at least) the rogue/bogus/malicious Cabinet.dll and DbgHelp.dll
eventually found in the directory it is started from ['] (the
"application directory").

For software downloaded with a web browser this is typically the
"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 Cabinet.dll or DbgHelp.dll get planted in the users "Downloads"
directory per "drive-by download" (or "social engineering") this
vulnerability becomes a remote code execution.

Due to the application manifest embedded in the executable which
specifies "requireAdministrator" the installer is started with
administrative privileges ("protected" administrators are prompted
for consent, unprivileged standard users are prompted for an
administrator password); execution of Cabinet.dll or DbgHelp.dll
then 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 Cabinet.dll in your "Downloads" directory, then copy it as
   DbgHelp.dll;

2. download eset_nod32_antivirus_live_installer_.exe and store it in
   your "Downloads" directory;

3. run eset_nod32_antivirus_live_installer_.exe from your "Downloads"
   directory;

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

PWNED!


Unsuspecting users who follow the guidance on ESET's web site
<http://www.eset.com/int/download/thank-you-eset-nod32-antivirus/file/13934/>

| (1) Download the .exe file to your computer and double-click
| it to start installation.

are the typical victims!

JFTR: I REALLY love (especially snakeoil) companies which don't
      protect or at least warn their customers from even the most
      trivial handling errors!


See <http://seclists.org/fulldisclosure/2015/Nov/101> 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.


Mitigation(s):
~~~~~~~~~~~~~~

0. DON'T USE EXECUTABLE INSTALLERS [°]!

   If your favourite applications are not distributed in the native
   installer package format of the resp. target platform: ask^WURGE
   their vendors/developers to provide native installation packages.
   If they don't: dump these applications, stay away from such cruft!

1. Turn off UAC's privilege elevation for standard users and installer
   detection for all users:

   [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System]
   "ConsentPromptBehaviorUser"=dword:00000000 ; Automatically deny elevation requests
   "EnableInstallerDetection"=dword:00000000

   See <https://technet.microsoft.com/en-us/library/dd835564.aspx#BKMK_RegistryKeys>

2. NEVER execute files in UNSAFE directories (like "Downloads" and
   and "%TEMP%")!

3. Deny execution (at least) in the "Downloads" directories and all
   "%TEMP%" directories and their subdirectories:

   * Add the NTFS ACE "(D;OIIO;WP;;;WD)" meaning "deny execution of
     files in this directory for everyone, inheritable to all files
     in all subdirectories" (use CACLS.EXE /S:<SDDL> for example);

   * Use "software restriction policies" resp. AppLocker.

   Consider to apply either/both to every "%USERPROFILE%" as well as
   "%ALLUSERSPROFILE%" alias %ProgramData%" and "%PUBLIC%": Windows
   doesn't place executables in these directories and beyond.

   See <http://home.arcor.de/skanthak/safer.html> as well as
   <http://mechbgon.com/srp/> plus
   <http://csrc.nist.gov/itsec/SP800-68r1.pdf>,
   <https://www.nsa.gov/ia/_files/os/win2k/application_whitelisting_using_srp.pdf>
   or <https://books.google.de/books?isbn=1437914926> and finally
   <http://www.asd.gov.au/infosec/top35mitigationstrategies.htm>!


stay tuned
Stefan Kanthak


[°] Self-extracting archives and executable installers are flawed^W
    b(rainde)ad in concept and dangerous in practice.

    DON'T USE SUCH CRUFT!
    ALWAYS use the resp. target platforms native package and archive
    format.

    For Windows these are .INF (plus .CAB) and .MSI (plus .CAB),
    introduced 20 years ago (with Windows 95 and Windows NT4) resp.
    16 years ago (with Office 2000).

    Both .INF and .MSI are "opened" by programs residing in
    %SystemRoot%\System32\ which are therefore immune to this kind
    of "DLL and EXE Search Order Hijacking" attack.
    Since both .INF and .MSI access the contents of .CAB directly
    they eliminate the attack vector "unsafe temporary directory"
    too.

['] A well-known and well-documented (trivial, easy to exploit and
    easy to avoid) vulnerability: 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>


Timeline:
~~~~~~~~~

2015-11-30    report sent to vendor

              NO answer, not even an acknowledgement of receipt

2015-12-12    report resent to vendor

              NO answer, not even an acknowledgement of receipt

2015-12-21    report published


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