Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Endpoint Security

1/28/2019
09:15 AM
Larry Loeb
Larry Loeb
Larry Loeb
50%
50%

'Steganography' Obsfucation Hides Old PDF Exploits From Antivirus Tools

EdgeSpot has found two new obsfucation methods to hide old PDF exploits from various antivirus tools.

Security firm EdgeSpot has been looking for PDF file exploits lately. Now, the firm's researchers have found two interesting ones.

The first is one that uses the PDF JS API this.getPageNumWords() and this.getPageNthWord() to "read" the Javascript contents on the PDF page. It executes the Javascript via eval(box).

This exploit is very similar to CVE-2013-3346, which was not obfuscated at that time of first discovery. Because of the obsfucation, it will bypass antivirus detection.

The obsfucation method that EdgeSpot researchers found could be used to hide other exploits besides this one.

After finding the first one, a second method of obsfucation was found a week later -- and it is potentially much more powerful.

(Source: iStock)
(Source: iStock)

It hides inside images in PDF files. This "steganography" method seems to be designed to once again hide from detection by AV engines. Specifically, researchers found that two layers of obfuscation were used in this exploit. The first layer is what they have previously discussed -- the method of "this.getPageNumWords()" and "this.getPageNthWord()". The exploit uses "this.getPageNumWords()" and "this.getPageNthWord()" to read and execute the Javascript hidden as “content."

The second layer is new and contains "Javascript content."

The API references say that these two APIs, working together, are used to read the stream of an image named "icon" which stored in the PDF file.

Looking at their sample’s Javascript code, researchers figured out that the code's function is to read and decode the "message" hidden in the icon's stream. Once it read the "message" successfully, it executes the "message" as Javascript code, via “eval(msg)”.

The icon stream, which is simply named "icon," could be saved as a "jpg" file and viewed in image viewer without problem.

This led the researchers to conclude that the attacker likely copied a project/technique called "steganography.js", which is open sourced. The project was developed working on browsers.

EdgeSpot researchers also believe the person or persons behind the PDF samples made their innovation as they successfully leveraged the technique in PDF format. They could not find any information mentioning this technique in PDF exploits previously, so they think this is the first time that the "steganography" technique has been used to hide PDF exploits.

By using this technique, all streams look normal, all images are viewable, and everything looks legitimate. This can probably explain why almost all AV engines missed it.

Old exploits can be dressed up to hide themselves from detection. Security teams have to be aware that such mutation may occur, and adjust their own techniques accordingly.

Related posts:

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
Edge-DRsplash-10-edge-articles
I Smell a RAT! New Cybersecurity Threats for the Crypto Industry
David Trepp, Partner, IT Assurance with accounting and advisory firm BPM LLP,  7/9/2021
News
Attacks on Kaseya Servers Led to Ransomware in Less Than 2 Hours
Robert Lemos, Contributing Writer,  7/7/2021
Commentary
It's in the Game (but It Shouldn't Be)
Tal Memran, Cybersecurity Expert, CYE,  7/9/2021
Register for Dark Reading Newsletters
White Papers
Video
Cartoon
Current Issue
Enterprise Cybersecurity Plans in a Post-Pandemic World
Download the Enterprise Cybersecurity Plans in a Post-Pandemic World report to understand how security leaders are maintaining pace with pandemic-related challenges, and where there is room for improvement.
Flash Poll
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2021-41086
PUBLISHED: 2021-09-21
jsuites is an open source collection of common required javascript web components. In affected versions users are subject to cross site scripting (XSS) attacks via clipboard content. jsuites is vulnerable to DOM based XSS if the user can be tricked into copying _anything_ from a malicious and pastin...
CVE-2021-41087
PUBLISHED: 2021-09-21
in-toto-golang is a go implementation of the in-toto framework to protect software supply chain integrity. In affected versions authenticated attackers posing as functionaries (i.e., within a trusted set of users for a layout) are able to create attestations that may bypass DISALLOW rules in the sam...
CVE-2020-19554
PUBLISHED: 2021-09-21
Cross Site Scripting (XSS) vulnerability exists in ManageEngine OPManager <=12.5.174 when the API key contains an XML-based XSS payload.
CVE-2020-35540
PUBLISHED: 2021-09-21
** REJECT ** DO NOT USE THIS CANDIDATE NUMBER. ConsultIDs: none. Reason: This candidate was in a CNA pool that was not assigned to any issues during 2020. Notes: none.
CVE-2020-35541
PUBLISHED: 2021-09-21
** REJECT ** DO NOT USE THIS CANDIDATE NUMBER. ConsultIDs: none. Reason: This candidate was in a CNA pool that was not assigned to any issues during 2020. Notes: none.