toolsmith: Malware Analysis with REMnux Docker Containers
Docker, runs on Ubuntu, Mac OS X, and Windows
ISSA Journal’s theme of the month is “Malware and what to do with it”. This invites so many possible smart-alecky responses, including where you can stick it, means by which to smoke it, and a variety of other abuses for the plethora of malware authors whose handy work we so enjoy each and every day of our security professional lives. But alas, that won’t get us further than a few chuckles, so I’ll just share the best summary response I’ve read to date, courtesy of @infosecjerk, and move on.
“Security is easy:
1) Don't install malicious software.
2) Don't click bad stuff.
3) Only trust pretty women you don't know.
4) Do what Gartner says.”
Wait, now I’m not sure there’s even a reason to continue here. :-)
One of the true benefits of being a SANS Internet Storm Center Handler is working with top notch security industry experts, and one such person is Lenny Zeltser. I’ve enjoyed Lenny’s work for many years; if you’ve taken SANS training you’ve either heard of or attended his GIAC Reverse Engineering Malware course and likely learned a great deal. You’re hopefully also aware of Lenny’s Linux toolkit for reverse-engineering and analyzing malware, REMnux. I covered REMnux in September 2010, but it, and the landscape, have evolved so much in the five years since. Be sure to grab the latest OVA and revisit it, if you haven’t utilized it lately. Rather than revisit REMnux specifically this month, I’ll draw your attention to a really slick way to analyze malware with Docker and specific malware-analysis related REMnux project Docker containers that Lenny’s created. Lenny expressed that he is personally interested in packaging malware analysis apps as containers because it gives him the opportunity to learn about container technologies and understand how they might be related to his work, customers and hobbies. Lenny’s packaging tools that are “useful in a malware analysis lab, that like-minded security professionals who work with malware or forensics might also find an interesting starting point for experimenting with containers and assessing their applicability to other contexts.”
Docker can be utilized on Ubuntu, Mac OS X, and Windows, I ran it on the SANS SIFT 3.0 virtual machine distribution, as well as my Mac Mini. The advantage of Docker containers, per the What Is Docker page, is simple to understand. First, “Docker allows you to package an application with all of its dependencies into a standardized unit for software development.” Everything you need therefore resides in a container: “Containers have similar resource isolation and allocation benefits as virtual machines but a different architectural approach allows them to be much more portable and efficient.” The Docker Engine is just that, the source from whom all container blessings flow. It utilizes Linux-specific kernel features so to run it on Windows and Mac OS X, it will install VirtualBox and boot2docker to create a Linux VM for the containers to run on Windows and Mac OS X. Windows Server is soon adding direct support for Docker with Windows Server Containers. In the meantime, if you’re going to go this extent, rather than just run natively on Linux, you might as well treat yourself to Kitematic, the desktop GUI for Docker. Read up on Docker before proceeding if you aren’t already well informed. Most importantly, read Security Risks and Benefits of Docker Application Containers.
Lenny mentioned that he is not planning to use containers as the architecture for the REMnux distro, stating that “This distribution has lots of useful tools installed directly on the REMnux host alongside the OS. It's fine to run most tools this way. However, I like the idea of being able to run some applications as separate containers, which is certainly possible using Docker on top of a system running the REMnux distro.” As an example, he struggled to set up Maltrieve and JSDetox directly on REMnux without introducing dependencies and settings that might break other tools but “running these applications as Docker containers allows people to have access to these handy utilities without worrying about such issues.” Lenny started the Docker image repository under the REMnux project umbrella to provide people with “the opportunity to conveniently use the tools available via the REMnux Docker repository even if they are not running REMnux.”
Before we dig in to REMnux Docker containers, I wanted to treat you to a very cool idea I’ve implemented after reading it on the SANS Digital Forensics and Incident Response Blog as posted by Lenny. He describes methods to install REMnux on a SIFT workstation, or SIFT on a REMnux workstation. I opted for the former because Docker runs really cleanly and natively on SIFT as it is Ubuntu 14.04 x64 under the hood. Installing REMnux on SIFT is as easy as wget --quiet -O - https://remnux.org/get-remnux.sh | sudo bash, then wait a bit. The script will update APT repositories (yes, we’re talking about malware analysis but no, not that APT) and install all the REMnux packages. When finished you’ll have all the power of SIFT and REMnux on one glorious workstation. By the way, if you want to use the full REMnux distribution as your Docker host, Docker is already fully installed.
After you’ve squared away your preferred distribution, be sure to run sudo apt-get update && sudo apt-get upgrade, then run sudo apt-get install docker.io.
REMnux Docker Containers
The first time you run a Docker container it will be automatically pulled down from the Docker Hub if you don’t already have a local copy. All the REMnux containers reside there, you can, as I did, start with @kylemaxwell’s wicked good Maltrieve by executing sudo docker run --rm -it remnux/maltrieve bash. Once the container is downloaded and ready, exit and rerun it with sudo docker run --rm -it -v ~/samples:/home/sansforensics/samples remnux/maltrieve bash after you build a samples directory in your home directory. Important note: the -v parameter defines a shared directory that the container and the supporting host can both access and utilized. Liken it to Shared Folders in VMWare. Be sure to run sudo chmod a+xwr against it so it’s world readable/writeable. When all said and done you should be dropped to a nonroot prompt (a good thing), simply run maltrieve -d /home/sansforensics/samples/ -l /home/sansforensics/samples/maltieve.log and wait again as it populates malware samples to your sample directory, as seen in Figure 1, from the likes of Malc0de, Malware Domain List, Malware URLs, VX Vault, URLquery, CleanMX, and ZeusTracker.
|Figure 1 – Maltrieve completes its downloads, 780 delicious samples ready for REMnux|
So nice to have a current local collection. The above mentioned sources update regularly so you can keep your sample farm fresh. You can also define your preferred DUMPDIR and log directories in maltrieve.cfg for ease of use.
Next up, a look at the REMnux MASTIFF container. “MASTIFF is a static analysis framework that automates the process of extracting key characteristics from a number of different file formats” from @SecShoggoth. I ran it as follows: sudo docker run --dns=my.dns.server.ip --rm -it -v ~/samples:/home/sansforensics/samples remnux/mastiff bash. You may want or need to replace --dns=my.dns.server.ip with your preferred DNS server if you don’t want to use the default 18.104.22.168. I found this ensured name resolution for me from inside the container. MASTIFF can call the VirusTotal API and submit malware if you configure it to do so with mastiff.conf, it will fail if DNS isn’t working properly. You need to edit mastiff.conf via vi with you API key and enable submit=yes. Also note that, when invoked with --rm parameters, the container will be ephemeral and all customization will disappear once the container exits. You can invoke the container differently to save the customization and the state.
You may want to also instruct the log_dir directive to point at your shared samples directory so the results are written outside the container.
You can then run mas.py /your/working/directory/samplename with your correct preferences and the result should resemble Figure 2.
|Figure 2 – Successful REMnux MASTIFF run|
All of the results can be found in /workdir/log under a folder named for each sample analyzed. Checking the Yara results in yara.txt will inform you that the while the payload is a PE32 it exhibits malicious document attributes per Didier Steven’s (another brilliant Internet Storm Center handler) maldoc rules as seen in Figure 3.
|Figure 3 – Yara results indicating a malicious document attributes|
The peinfo-full and peinfo-quick results will provide further details, indicators, and behaviors necessary to complete your analysis.
Feed said script to JSDetox under the Code Analysis tab, run Analyze, choose the Execution tab, then Show Code and you’ll quickly learn that the obfuscated code serves up a malicious script from palwas.servehttp.com, flagged by major browsers and Sucuri.net as distributing malware and acting as a redirector. The results are evident in Figure 5.
|Figure 5 – JSDetox results|
All the malware analysis horsepower you can imagine in the convenience of Docker containers, running on top of SIFT with a full REMnux install too. Way to go, Lenny, my journey is complete. J
Lenny’s plans for the future include maintaining and enhancing the REMnux distro with the help of the Debian package repository he set up for this purpose with Docker and containers part of his design. Independently, he will continue to build and catalog Docker containers for useful malware analysis tools, so they can be utilized with or without the REMnux distro. I am certain this is the best way possible for you readers to immerse yourself in both Docker technology and some of the best of the REMnux collection at the same time. Enjoy!
Ping me via email or Twitter if you have questions (russ at holisticinfosec dot org or @holisticinfosec).
Cheers…until next month.
Thanks again to Lenny Zeltser, @lennyzeltser, for years of REMnux, and these Docker containers.