Deep Inside Malicious PDF documents

When we start to check the PDF files that exist in our Pc or Laptop we may use antivirus scanner but in this days it seems not good enough to detect malicious PDF that counties a shell code because, as attacker mostly encrypt it’s count -ant to bypass the antivirus scanner and in many times target a zero day vulnerability that exit in Adobe Acrobat reader or in updated version.
Before we start analyze malicious PDF we going to have a simple look at PDF structures as to understand how the shell code work and where it locate.

PDF components
PDF Header
The first line of pdf show the pdf format version the most important line that give to you the basic information of the pdf file for example “%PDF-1.4 means that file fourth version.

PDF Body
The body pdf file consist of objects that compose contents of the document, these objects include fonts, images, annotations, text streams and user can put invisible objects or elements, this objects can interactive with pdf features like animation, security features. The body of the pdf supports two types of numbers (integers, real numbers).

The Cross-Reference Table (xref table)
The cross- reference counties links of all objects and elements that exist on file format, you can use this feature to see other pages contents (when the
users update the PDF the cross-reference table gets updated automatically).

The Trailer
The trailer contains links to cross-reference table and always ends up with %%EOF to identify the end of a PDF file the trailer enables a user to navigate to the next page by clicking on the link provided.

Malicious PDF through Metasploit
Now after we have talking a tour inside PDF file format and what it contains we will start to install old version of Adobe Acrobat reader 9.4.6 and 10 through to 10.1.1 that will be vulnerable to Adobe U3D Memory Corruption Vulnerability. This exploit are exist in Metasploit framework so we going to create the malicious PDF and analysis it in KALI Linux distribution. Start opens the terminal and type msfconsole. We going to setting some Metasploit variables to be sure that everything is working fine.

*After choosing the exploit type we going to choose the payload that will execute during exploitation in the remote target and open Meterpreter session. The file has been saved on /root/.msf4/local.

So we going to move the file to Desktop for easier located by typing in the terminal
root@kali :~# cd /root/.msf4/local
root@kali :~# mv msf.pdf /root/Desktop

PDFid
Now we going to use pdfid to see what the pdf continue of elements and objects and JavaScript and see if something interesting to analyze. The PDF has only one page maybe its normal. There are several JavaScript objects inside… this is very strange. There is also an OpenAction object which will execute this malicious JavaScript So we going to use peepdf.

Peepdf
Peepdf its python tool very powerful for PDF analysis, the tool provide all necessary components that security researcher need in PDF analysis without using many tools to do that, it support encryption, Object Streams, Shellcode emulation, Javascript Analysis, and for Malicious PDF it Shows potential Vulnerabilities, Shows Suspicious Elements, Powerful Interactive Console, PDF Obfuscation (bypassing AVs), Decoding:
hexadecimal – ASCII and HEX search.

Analysis
If we going to start analysis go to the directory of the PDF file then start with syntax /usr/bin/peepdf–f msf.pdf.
*choose the LHOST which is our IP address and we can view through typing ifconfig in new terminal
*finally we type exploit to create the PDF file with configuration we created before

We use –f option to avoid errors and force the tool to ignore them. This the default output but we see some interesting things first one we see is the highlighted one object 15 continue JavaScript code and we have also one object 4 continue two executing elements (/AcroForm & /OpenAction) and the last one is /U3D showing to us Known Vulnerability for now we will start to explore this objects by getting an interactive console by typing syntax /usr/bin/peepdf –i msf.pdf

The tree commands shows the logical structure of the file, and starting explore object 4 (/Acro-Form).
When we type object 4 it gave you another objects to explore for now we didn’t see any impotent information or seems suspicious except object 2 (XFA array) that gave us the element <fjdklsaj fodpsaj fopjdsio> and seems to us not continue something special. Let’s move to the another object (Open Action).
Now we can see JavaScript code, that will be executed when the pdf file will be opened. The other part of the JavaScript code is barely obfuscated like writing some variables in hex and in this code we can see a heap spraying with shell code plus some padding bytes. The attackers typically use unicode to encode their shell code and then use the unescape function to translate the unicode representation to binary content (now we are sure that defiantly a malicious pdf)

Defend
We defend our network from that type of malicious files by providing strong e-mail and web filter, IPS and by application control: disable JavaScript and Disable PDF rendering in browsers, Block PDF readers from accessing file system and Network resources. Security awareness.

New way of ATM ‘Eavesdropping’ attacks

This week, Global ATM manufacturer NCR Corp issued an alert about card reader eavesdropping attacks, which was first identified in Europe last year and are spreading now across the world. These attacks involve accessing or opening the top of an ATM’s enclosure, where the card reader is housed, and attaching a so-called wiretapping or eavesdropping device to the reader. The attackers’ device captures card data as it is transmitted from the card reader to the ATM.

Earlier attacks, which were targeting through-the-wall ATMs typically installed right outside a bank branch, involved drilling a hole or cutting into the ATM’s enclosure to insert and attach the device to the card reader.

Now, however, NCR says fraudsters have changed their technique by targeting stand-alone, lobby-style ATMs, which are commonly placed in retail locations, and opening ATM enclosures either by picking the physical locks or opening the machines with commonly used electronic access keys or codes.

An electronic data tapping and storage device similar to those seen in other eavesdropping attacks is then attached directly to the card reader. Unlike eavesdropping attacks carried out by drilling a hole in the ATM fascia (which is then disguised with a sticker or other cover) this version leaves no visible trace of the breach on the exterior of the ATM, the alert said.

It’s far too common for banks to continue to use the default electronic access keys or codes programmed by the original equipment manufacturer before ATMs are shipped out. And these codes often are universal, such as 1234, especially for certain makes and models.

“If merchants, or other off-premises ATM deployers, fail to change default keys or codes, they’re leaving themselves open to attack.”

Thus, if banks and merchants don’t change these codes when they install and deploy their ATMs, they leave themselves open to easy attack, because criminals can readily find these default codes on the Internet, in underground forums or even product or repair forums.

How it works?

Eavesdropping involves the interception of card data while it’s in transit, not skimming data from a magnetic-stripe as the card is inserted into the ATM. That makes these attacks tricky to detect and thwart, because it bypasses anti-skimming technology ATM manufacturers have for years pushed out to the market, Wild says.

But some anti-skimming solutions that alert banks or merchants when ATM enclosures are opened would at least raise a flag that something is amiss. Still, eavesdropping attacks are just another example of how fraudsters are constantly perfecting their techniques. “There is never going to be a single solution that stops everything,” Wild says.

Picture-Based Malware Attacks are New Trend

Making a resurgence among malware writers is steganography, which means to hide in plain sight, according to Dell Security’s Cyber Threats Unit.
The Stegoloader malware family, also known as Win32/Gatak.DR (Microsoft) and TSPY_GATAK.GTK (Trend Micro), appears to target healthcare, education, and manufacturing, and it does so with a seemingly innocent Portable Network Graphics (PNG) picture of the Earth in space.
Steganography, which combines the Greek words for “covered, concealed, or protected” with “writing,” was first coined around 1499 in a book, Steganographia, by Johannes Trithemius.
While the book was supposed be on magic it was actually about cryptography and steganography. Other examples include using the first letter of each printed line to spell out an alternative message.
For digital steganography, the secret message is embedded within the code of a document or image. In some cases the addition of a message will bloat the file so that it stands out as being changed or different.
However, newer techniques appear to address that concern.
For example, a malware creator might take a cute picture of a kitten and alter the color code of every 50th pixel to produce a desired alphanumeric, or alter the least significant byte to correspond to an alphanumeric.
The result would have a nominal increase in file side and be so subtle that analysis would be needed to identify the exact alterations.
Stegnoloader hides its main module’s code inside a PNG image. This is not exactly new. A variant of the Zeus banking Trojan used sunset pictures.
Another malware family hid malicious content inside an Android icon image, dnd the terrorist group Al Qaeda is known to have a used steganography in videos to communicate with its followers.
One advantage to using steganography is that most antivirus products do not actively scan image files for malware. According to Dell, another way Stegoloader attempts to avoid detection is the strings found in the binary are constructed in the program stack before being used.
However, Stegoloader will not execute if it finds there is active analysis or security tools installed on the infected system.
After downloading a PNG image from a URL hardcoded into the file, Stegoloader decompresses the image, accesses each pixel, and extracts the least significant bit from each color of each pixel.
Neither the PNG image nor the decoded messages are stored on the infected system’s hard drive in an attempt to be evasive.
The Stegoloader family is known to be distributed through a software piracy site. The malicious code includes modules that gather geographic location data, victims’ browsing history, passwords, and lists of recently opened documents.
At the moment Stegoloader appears to be only gathering intelligence.
Steganography has been used in operating botnets in recent years. The TDSS botnet used JPG images hosted on popular blogging sites for its Command & Control (C&C) communication, and ShadyRAT was also able to decrypt and decode C&C commands hidden within JPG files.
“It is my intuition that they might be selling compromised hosts to others,” Pierre-Marc Bureau, CTU senior security researcher, told SCMagazine.
“But they do not appear to be trying to build a big botnet. They are not trying to accumulate thousands upon thousands of infected hosts. I really think they are trying to find interesting networks [or] hosts.”
It should be noted that steganography does not always use pictures. The Morto Trojan, for example, actually hides its C&C traffic within simple DNS requests. Morto requests a non-existent domain from a hard-coded DNS server which is the actual C&C server.
The commands are embedded and obfuscated by a simple Base64 encoding within the DNS response. However, the DNS response is much larger than it needs to be and would therefore be suspicious on its own.