Monthly Archives: February 2014

Reverse-Engineering and Malware Analysis

malwareLast year I had the chance to go to SANS Orlando 2013 in Orlando, Florida – thank you Wes! – which is one of the yearly’s biggest SANS conferences only outpaced in size by SANS FIRE in Baltimore, Maryland.  I went there to take the 5 days course – FOR 610 Reverse-Engineering Malware: Malware Analysis Tools and Techniques – with Lenny Zeltser. Apart of the course the main choice was due to the instructor. Lenny is a brilliant fellow and top rated SANS instructed. Awesome writer and fantastic lecturer.

I was very enthusiastic about taking out the most of it. One reason was  because I had read the Malware Fighting  Malicious Code book from Ed Skoudis where Lenny wrote chapter 2 and 4.  This book is 10 years and it’s still a classic, a historical object and definitely a must read to someone who is part of the security community. Other reason was that l wanted to get the skills to be capable of securely analyze, debug, and disassemble malicious programs in order to translate this capability into actionable threat intelligence.

On the first day of the training we got introduced to 2 approaches to examine malicious programs. Behavior analysis and static/code analysis. To perform this we started by setting up a controlled and isolated environment. A simple and inexpensive malware analysis lab running on VMware. Using this lab we used a set of free tools that allowed us to determine what the malicious program does and how it interacted with the file system, network, registry and memory. We also got introduced to REMnux . A lightweight Linux distribution for assisting malware analysts with reverse-engineering malicious software. The distribution is based on Ubuntu and is maintained by Lenny Zeltser.  Using a set of Windows tools, the REMnux distro plus a variety techniques we  got a better understanding how we could analyze malware and determine its capabilities.  Then we got deeper in order to make a detailed analysis of the malware by using reverse engineering tools and different methods. By using techniques to find strings in the executable, run a disassembler (IDA Pro),  load the executable into a debugger (OllyDbg) and execute it and look at the API calls being made we got a glimpse in the world of code analysis. After the lab was set and we got an understanding of the processes we will follow the fun started! With several hand-on labs and different specimens we observed what the malware does and we could document the findings and translate them into indicators of compromise and actionable intelligence that can be used to proactively detect and monitor threats.

Day two started with additional malware analysis approaches. We started to get introduced into packed executable’s and what patching means. Also we unpacked malicious executables using simple packing techniques. Here is where we began the journey on x86 Intel assembly. On the second half of day two we covered browser malware and flash based malware and how to use REMnux to use behaviors and code analysis techniques to analyze web malware. It was impressive to see the amount of ingenious techniques enforced by the bad guys to deliver malicious stuff.

Day three is a deep dive into malicious code analysis. Its starts with core reversing engineering concepts and you spend the rest of the day playing with malicious code at the assembly level. It’s the all day looking at a dissasembler and a debugger. Throughout the material and the exercises you get more and more exposed to x86 assembly stuff. We manage to use the debugger to control malicious program execution (step in, over, breakpoints) and monitor or change its state (registry and memory).   On this day we also covered user mode rootkits, key loggers, sniffers, DLL injection and downloader’s – great stuff!

Day four, even after 10 hours sleep I doubt I had enough processing power on my neurons to absorb all Lenny had to say. As complementary strategy I gave a lot of use to my pencil and wrote as much notes as possible in my courseware material. During the first half of the day we were shown the techniques that the malware writes use to protect their programs. Packing was one. But more complex techniques such as anti-disassembly, anti-debugging and anti-VMware and others were demonstrated. It’s an extraordinary arms race between good and evil. A huge amount of hands on exercises were made so we could reinforce all these concepts and techniques. Was also amazing to see Lenny describing how different malware specimens use mazes of code and junk code to frustrates the analyst and mislead him. By enforcing this techniques, in case the analyst does not have enough resources (time/money) he will soon stop doing his analysis and move on to something else – Evil will win – an interesting trade-off. Apart of the techniques we were taught different techniques to bypass those malware defenses. One example was to infect a system with a piece of malware that was packed/obfuscated. When execute, the malware  loaded its unpacked code into memory which allowed us to examine it. By staying resident in memory because in the file system it was encrypted we used techniques do dump it from memory. To do this we used Chimprec to extract the process from memory and then rebuilding its  PE header import table in order to be executed. Other technique was the usage of a debugger to patch an executable to avoid anti-debugging mechanism. Other tools like LordPE and OllyDump are also used. On the second half of the day, shellcode analysis and Web malware anti-deobfuscation techniques were described and practiced.

Finally on day 5 we spent the first half of the day learning the techniques and tools for analyzing malicious Microsoft Office (Word, Excel, PowerPoint) and Adobe PDF documents. The second half of the day is spent on memory analysis forensics with the help of Volatility Framework and associated plug-ins. The course ends with explanation of the different techniques used by root kit infections and its deceptive techniques and how you could use memory and code analysis to determine and un-hide their capabilities.

The course is extremely technical and deep and very hands-on. I was overwhelmed with the amount of information. After day 3 I was feeling like I was drinking from the fire hose. The course is part of the SANS digital forensics and Incident response curriculum. It is very well structured and the sequential steps it follows are very well thought out.

This particular security field is a very interesting one, it will continue to evolve and it is challenging. Also as the security industry continues to progress from a reactive approach to a more proactive one, the malware analyst type of skills will have an increased demand. More and more companies are funding their own threat intelligence operations with this kind of capability in-house.

If you are an incident handler, sysadmin, researcher or simple want to be the next digital Sherlock Holmes you may also want to look into the Malware Analyst’s Cookbook and DVD: Tools and Techniques for Fighting Malicious Code book and the Practical Malware Analysis. Other relevant and free resources are the Dr. FU’s Security blog on Malware analysis tutorials. Thet Binary Auditing site which contains free IDA Pro training material.  Finally, the malware analysis track  in the Open Security Training site is awesome. It contains several training videos and material for free.

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