The Jock Becomes the Geek

Sunday, February 22, 2015 Posted by Corey Harrell 2 comments
We interrupt the normal DFIR programming on this blog for a different kind of post. A post about a situation I found myself in. It's a story others may find amusing or cause them to have empathy for me. It's a story about how I evolved from being a jock to walking amongst the DFIR geeks.

In high school I didn't pay any mind to the so called “clicks.” If I had to be categorized then I guess it would had been a jock. I was a three sport athlete who enjoyed the social life outside of school. I wasn’t in to any of the things people tend to talk about to show their “geek credentials.” I didn’t care about technology (outside of video games), didn’t use computers, and definitely didn’t play any of the so called “geeky” games like dungeons and dragons. Heck, I didn’t even have a drive to learn since I was only going through the motions.

So at this point you may be wondering what the hell happened to me. To go from an athlete who didn't care about technology and learning. To someone who is passionate about one of the most technical areas within the information security field and spends their free time researching “geeky” things. What happened to me was a life changing experience.

After I graduated high school I was working for an organization who provided for people with disabilities. I have the upmost respect for the people whose calling is in this field. To care for one of the most vulnerable populations in our society. Without these organizations, there is a risk to returning to the institutions where this population was mistreated and abused for years. The people working in this field have been some of the most caring people I ever met. My mom was one of them and growing up she would bring me to the places where she worked. Now back to my story. I was a floater in the organization I worked for. Floaters worked in the residences where the people lived and did not have a set house they would always work in. We floated from house to house based on where coverage was needed. The houses varied in the people’s functional levels who lived there. Some had high functioning individuals who had jobs and took care of themselves; my job was more of a mentor then a direct care worker. Other houses had lower functioning individuals; my job was direct care taking care of their every need. Going in to this job I knew what I was in for and what the nature of the work could involve.

One day I was working at a low functioning house. During my shift, an individual who was confined to a wheel chair had an accident that involved a bowel movement. I wasn't sure how it played out with my coworker but it was my turn. It was the turn of an 19 year old kid to clean up an adult who had an accident. I worked in this position for some time but this was the first time I encountered having to attempt anything like this. As we entered into the bathroom I noticed the most awful smell I have ever smelled. Mind you, we just walked in to the bathroom and the bowel smell quickly overcame what little fresh air was left in the room. I started to envision what I had to do next. The images running through my mind along with the smell was making me more and more nauseous. That is when I blew chunks in the direction of the toilet as I dropped to my knees getting sicker and sicker as tears started rolling down my face. I mumbled and grunted to my coworker; something along the lines "I can't. I can't. I can’t. I can't stop getting sick." She was one of the people I worked with who had a serving heart but looking back on this almost 18 years later I think she took pity on me. An 19 year old kid who looked like a mess and was on his knees throwing up into the toilet. Each time I breathed in what smelled worse than death resulted in the toilet calling my name again. I tried to leave. Believe me, I tried to leave to get fresh air. Boy, how many times did I try to leave? The smell; that horrible, horrible smell. At one point, I stood up to leave and I saw my coworker attending to the individual. That provided visuals to go along with the smell and things became worse.

I don't remember how long this went on for or what happened afterwards. All I know was this experience had a significant impact on my life. Again, I have the upmost respect for those who work in this field but the experience taught me the work was not meant for me and my weak stomach. The experience stuck with me and impacted me when I was joining the Marines a year later. I had the pick of any job I wanted in the Marines. I only wanted a job that kept me far away from going through the experience again. I picked what in my mind was the complete opposite of the field where I had this experience. I picked a technology field where I thought I would never again be responsible for caring for other people. (Please keep in mind, when I made this decision I was 19 and had a lot to learn.) This decision –based on my experience - is what made the jock become a geek. The rest of my story is history as I had a guiding hand leading me down the path where I eventually found my passion amongst the DFIR geeks. A community where if you have the technical skills and knowledge then you are accepted as one of their own even if you lack the traditional "geek credentials."

Process Hollowing Meets Cuckoo Sandbox

Wednesday, February 4, 2015 Posted by Corey Harrell 2 comments
Growing up I loved to watch horror movies. In hindsight, they scared the crap out of me probably because I was too young to watch them. One such movie was the 1986 movie Night of the Creeps. Alien slugs enter through peoples' mouths and eventually take over their bodies. A classic body snatchers style movie that had me worried for few days when talking to close to people. Process hollowing (aka process replacement) is a technique malware uses to overwrite a running process with a malicious code. To me it's the technical equivalent of those alien body snatchers. This post explores process hollowing techniques using the Cuckoo Sandbox.

Process Hollowing (aka Process Replacement)

In my post Prefetch File Meet Process Hollowing I walked through what process hollowing was but for completeness I’ll copied what I wrote below:

Malware uses various techniques to covertly execute code on systems. One such technique is process hollowing, which is also known as process replacement.

The book Practical Malware Analysis states the following in regards to this technique:

"Process replacement is used when a malware author wants to disguise malware as a legitimate process, without the risk of crashing a process through the use of process injection.

Key to process replacement is creating a process in a suspended state. This means that the process will be loaded into memory, but the primary thread of the process is suspended. The program will not do anything until an external program resumes the primary thread, causing the program to start running"

In addition, the book The Art of Memory Forensics states the following:

"A malicious process starts a new instance of a legitimate process (such as lsass.exe) in suspended mode. Before resuming it, the executable section( s) are freed and reallocated with malicious code."

In essence, process hollowing is when a process is started in the suspended state, code is injected into the process to overwrite the original data, and when the process is resumed the injected code is executed. Everything about the process initial appears to reflect the original process. Similar to how everything about the person initially appears to be the original person. Upon closer inspection it reveals that everything is not what it seems. The process behaves differently (such as network communications) and the code inside the process is not the original code. This is very similar to the person behaving differently (such as trying to eat you) and the biological material inside the person is not the original biological material.

A Common Process Hollowing Technique

Through observation, the characters in the In the Night of the Creeps figured out how people’s bodies were snatched. Slugs went from one person’s mouth to another person’s mouth. After observing this method the characters put tape over their mouths and were able to fight the zombies without becoming one themselves. By knowing what technique was used to snatch a body enabled the characters to defend themselves. The same can be said about process hollowing and knowing how the technique looks enables you to spot the zombified processes. One of the more publicize techniques was described in the Practical Malware Analysis book (lab 12-2 solution on page 590) as well as Trustwave SpiderLabs’s article Analyzing Malware Hollow Processes. The sequence of Windows functions, their descriptions, and how they appear during dynamic analysis of the Profoma Invoice.exe sample (md5 ab30c5c81a9b3509d77d83a5d18091de) with the Cuckoo sandbox is as follows:

        - CreateProcessA: creates a new process and the process creation flag 0x00000004 is used to create the process in the suspended state
        - GetThreadContext: retrieves the context of the specified thread for the suspended process
        - ReadProcessMemory: reads the image base of the suspended process
        - GetProcAddress: according to Practical Malware Analysis this function “manually resolves the import UnMapViewofSection using GetProcAddress, the ImageBaseAddress is a parameter of UnMapViewofSection”. This removes the suspended process from memory.
        - VirtualAllocEx: allocates memory within the suspended process’s address space
        - WriteProcessMemory: writes data of the PE file into the memory just allocated within the suspended process
        - SetThreadContext: according to Practical Malware Analysis this function sets the EAX register to the entry point of the executable just written into the suspended process’s memory space. This means the thread of the suspended process is pointing to the injected code so it will execute when the process is resumed
        - ResumeThread: resumes the thread of the suspended process executing the injected code

Cuckoo Sandbox Showing the Common Process Hollowing Technique

Cuckoo Sandbox is an open source automated malware analysis system. In their own words "it simply means that you can throw any suspicious file at it and in a matter of seconds Cuckoo will provide you back some detailed results outlining what such file did when executed inside an isolated environment." Malwr is a free online malware analysis service that leverages the Cuckoo Sandbox. The Behavioral Analysis section outlines the function calls made during execution. The pictures below show the Profoma Invoice.exe sample’s (md5 ab30c5c81a9b3509d77d83a5d18091de) function calls that perform process hollowing.

The image below shows Profoma Invoice.exe creating a process in the suspended state. The suspended process’ handle is 0x00000088 and thread handle is 0x0000008c.

The next image shows Profoma Invoice.exe retrieving the context of the suspended process since it references the thread handle 0x0000008c.

The image below shows Profoma Invoice.exe reading the image base of the suspended process since it references the process handle 0x00000088.

The image below shows Profoma Invoice.exe getting the addresses of the UnMapViewofSection and VirtualAllocEx function calls.

The images below show Profoma Invoice.exe writing a PE file into the address space of the suspended process since it references the process handle 0x00000088. It takes multiple WriteProcessMemory function calls to write the entire PE file.

The image below shows Profoma Invoice.exe setting the thread context for the suspended process since it references the thread handle 0x0000008c.

The image below shows Profoma Invoice.exe resuming the suspended thread to execute the injected code.

Cuckoo Sandbox Detecting the Common Process Hollowing Technique

Cuckoo Sandbox detects malware functionality using signatures. The image below shows Malwr detecting the common process hollowing technique used by Profoma Invoice.exe (md5 ab30c5c81a9b3509d77d83a5d18091de).

The signature detecting process hollowing reports it as “executed a process and injected code into it, probably while unpacking.” The signature detecting the technique is named and is available in the Community Signatures. The signature is open allowing anyone to read it to see how it detects this behavior. However, the image below shows a portion of the signature that detects the sequence of function calls outlined earlier to perform process hollowing.

A Different Process Hollowing Technique

The process hollowing technique outlined above is well publicized and is the technique I normally expected to see. It was as if I had tape on my mouth waiting for a zombified friend to come strolling down the street. There are more than one ways to perform an action similar to there being more than one way to snatch a body. In the 1998 movie The Faculty an unknown creature snatched bodies by entering the body through the ear. Now imagine what would had happened to the characters from the Night of the Creeps movie encountering these body snatchers. The zombified bodies are harder to spot since they don’t look like zombies. Trying to defend themselves with tape on their mouths and baseball bats in hand would be short lived. The tape offers no protection since the creatures enter through the ear. It’s a different technique with the same result. Process hollowing is similar with different techniques ending with the same result.

I was a bit surprised back in December when I saw the behavior in the image below after I ran the sample Kroger_OrderID.exe (md5 1de7834ba959e734ad701dc18ef0edfc) through a sandbox.

The behavior clearly shows that Kroger_OrderID.exe is going to perform process hollowing since it started the svchost.exe process in a suspended state (creation flag 0x00000004.) However, the function calls afterwards are not the typical well publicized ones; this was a different technique. After a bit of searching I found the Lexsi article Overview of the Kronos banking malware rootkit, which breaks down how this technique works. (the article also shows how to use Volatility to analyze this as well.) I summarized below the Windows function sequence and their descriptions as outlined in the article:

        - CreateProcessA: creates a new process and the process creation flag 0x00000004 is used to create the process in the suspended state
        - ReadProcessMemory: reads image base of the suspended process
        - NtCreateSection: creates two read/write/execute sections
        - ZwMapViewOfSection: maps the read/write/execute sections into the malware’s address space
        - ZwMapViewOfSection: maps the second section into the suspended process’s address space (this section is therefore shared between both processes).
        - ReadProcessMemory: reads image base of the suspended process’s image into section 1
        - ReadProcessMemory: reads image base of the malware’s image into section 2
        - NtMapViewOfSection: overwrites the suspended process's entry point code by mapping section 1 to the new process base address
        - ResumeThread: resumes the thread of the suspended process executing the injected code

Cuckoo Sandbox Showing the Different Process Hollowing Technique

The Behavioral Analysis section outlines the function calls made during execution. The pictures below show the sample Kroger_OrderID.exe (md5 1de7834ba959e734ad701dc18ef0edfc) function calls performing the different process hollowing technique.

The image below shows the first three function calls. The sample Kroger_OrderID.exe creates a suspended process with the thread handle 0x00000608 and process handle 0x00000604. Next the ReadProcessMemory function reads the image base of the suspended process due to the reference to process handle 0x00000604. The NtCreateSection function then creates the second read/write/execute section with the section handle 0x000005f8.

The image below shows the next three function calls. The ZwMapViewOfSection function maps the read/write/execute sections into the malware’s address space due to the section handle 0x000005f8 being referenced. The next ZwMapViewOfSection maps the second section into the suspended process’s address space due to both the section handle 0x000005f8 and process handle 0x00000604 both being referenced. Then the ReadProcessMemory function reads malware’s image into the section. Not shown in the image is the ReadProcessMemory function referencing the process handle 0x00000604.

The image below shows the remaining four functions. The NtCreateSection function then creates the first read/write/execute section with the section handle 0x000005f4. The ZwMapViewOfSection functions maps the read/write/execute sections between the malware and suspended process due to section handle 0x000005f4 and process handle 0x00000604 both being referenced. This mapping overwrites the entry point code in the suspended process. Finally, the ResumeThread function resumes the thread of the suspended process executing the injected code.

Cuckoo Sandbox Detecting the Different Process Hollowing Technique

**** Updated on 02/04/15 *****

This section of the blog has been edited since it was published earlier today. In the original blog post I highlighted how the signature did not detect this injection technique and I shared a signature I put together to detect it.

Brad Spengler sent me an email about what I was seeing. He mentioned that a change did not make it into the updated signature. Specifically, he mentioned the plugin is looking for NtMapViewOfSection which he uses in his Cuckoo Sandbox instead of looking for the older ZwMapViewOfSection. I modified the signature by renaming NtMapViewOfSection to ZwMapViewOfSection (on lines 45 and 51) and afterwards it did detect this technique. As a result, I updated this section of the blog to reflect this since this post’s purpose was to explore different injection techniques and how Cuckoo can help explore them.

**** Updated on 02/04/15 *****

Cuckoo Sandbox is able to detect this different process hollowing technique (see update about change made to the signature.) Executing the sample Kroger_OrderID.exe (md5 1de7834ba959e734ad701dc18ef0edfc) in Cuckoo results in the following behavior detection.


Wrapping Things Up

We don’t need to sit at our computers wearing headphones and tape on our mouths to hunt down zombified processes within our environments. Process hollowing is an interesting technique and it constantly reminds me about the various body snatcher horror movies I’ve seen. Leveraging the Cuckoo Sandbox makes exploring the various process hollowing techniques even more interesting since it allows for following the sequence of Windows function calls.

Happy hunting and if you come across any zombies in your travels don’t take any chances and just follow the rule from the movie Zombieland. Rule 2 Double Tap: when in doubt, don't get stingy with your bullets.

Linkz for Detection and Response

Monday, January 19, 2015 Posted by Corey Harrell 1 comments
The fastest way to reach a destination is to learn from those who have traveled parts of the journey you are on. Others may point you in a direction to avoid the obstacles they faced or show you the path through the woods towards your destination. In Information Security, we tend to gain knowledge from others by what they publish: websites, blogs, books, and even their 140 character tweets. The journey I have been on is exploring enterprise security detection and response; actually implementing enterprise detection and response. Implementing them not as standalone processes standing on their own but two complimentary processes that feed into each other. This Linkz post is sharing the works by others I came across whose focus is on detection and response.

Linkz for Incident Response and SIEM

I shared these linkz before but they point to some great resources about detection and response. For linkz related to incident response - including the thought process behind IR - refer to the post Linkz for Incident Response. For linkz related to detection with a focus on SIEM refer to Linkz for SIEM.

Network Security Operations Management Workflow

When it comes to network security there is a wealth of information. How to create a SOC, how to design and deploy IDS sensors, and how to use security monitoring tools are a few of the topics covered. Despite the wealth of information, there is very little about the management workflow for network security monitoring. Securosis released the Network Security Operations Quant Report about five years ago and it outlines one of the best management workflows I have come across. The Manage Process (on page 13) addresses policy review, update policies & rules, evaluate signatures, deploy, and audit/validate. It's a decent process since it touches on topics I haven't seen addressed elsewhere. At this point I could care less about the metrics portion of the document but the process portion is worth a look.

Network Security Monitoring Books

One thing I tend to look for in detection and response resources is do they outline a process or a thought process. Tools are great and all but it's pretty easy to learn a tool on your own compared to the process one  should use when doing detection and response. The processes are what you can learn from others to reach your destination and you can fill in the gaps by teaching yourself the tools. The next two resources are not free but are well worth the investment. Richard Bejtlich's The Practice of Network Security Monitoring: Understanding Incident Detection and Response and Chris Sanders  & Jason Smith's Applied Network Security Monitoring: Collection, Detection, and Analysis. Both books cover open source NSM tools and analyzing network data but the aspects I really enjoyed where their perspectives. Their perspectives about how to approach NSM and how to manage certain aspects of NSM including the response to security incidents along with detection security events.

Free Book with Strategies for Cybersecurity Operations Center

Carson Zimmerman of The MITRE Corporation released a free book titled Ten Strategies of a World-Class Cybersecurity Operations Center. I have been to a few different conferences where vendors give out free books. Needless to say, based on my past experiences I view free books with skepticism. However, Ten Strategies of a World-Class Cybersecurity Operations Center has restored my faith in free books. I'm surprised it was released for free; the content was great and the quality was top notch. The strategies covered topics from consolidating functions of detection and response under one organization to CSOC size to staff quality to sensor placement to responding to incidents. It's a great read for anyone who is looking to improve an organization's detection and response capability. It may even be worth the while for people who have been managing CSOCs to pick up a few different ideas.

Leveraging the Kill Chain for Detection

Sean Mason wrote the article Leveraging The Kill Chain For Awesome discussing the various ways the kill chain can be used. The section I wanted to focus on was the following: "when it comes to enterprise detection, the Kill Chain is useful for understanding what your capabilities are, as well as your gaps in coverage by tools and threat actors." This is one area where I think the kill chain excels. By organizing your detection rules beneath the kill chain it is easy to see what detection areas are strong and weak. Furthermore, it helps to see where external tools or intelligence can fill in the gaps. The one additional point I suggest is to do this organization for each use case that is implemented.

Questions to Answer During Response

A couple months ago Jack Crook put together a nice post over on his HandlerDiaries blog called Answering those needed questions. He walked through the typical questions he needs to answer when he is responding to an incident. In addition, he addressed "some of the actions needed during response activities." There were two things I really enjoyed about the post. First was how he broke down all of the possible questions one could ask into six categories; this simplifies the thought process making it easier to work through. The second point I liked was how he tied together response and detection. Throughout the post he touched on things to consider to improve detection as you respond.

Triage Questions

Continuing along with what questions should be answered when responding to security incidents is David Bianco's article Triage Any Alert With These Five Weird Questions!. David defines alert triage as "the process of going through all of your alerts, investigating them, and either closing them or escalating them to an incident." By far, this is one of the most common activities for those performing detection and response. The article walks through five questions one should ask while performing alert triage. The article is well worth the read since it highlights things to consider when performing this work.

If Antivirus Fires Triage that System

Speaking about triaging and alerts. Adam over at the Hexacorn blog put together an awesome post (The art of disrespecting AV (and other old-school controls), Part 2) highlighting a critical point. His conclusion was "when you see an AV alert you need to triage the system, because it has been compromised + there may be still some undetected malware present on it." I couldn't agree more with the items he brought to light in his post and his conclusion. Too many times you see organizations complacent in that their antivirus solutions detected and removed a malware without any additional work or trying to answer questions. Too many times I've seen where antivirus hits on one file but missed numerous others. The line of thinking things are all good "since antivirus got it" is broken and in the end risks leaving compromise systems on the network. Furthermore, triaging every single antivirus alert provides visibility into the network and the methods being used trying to compromise an organization.

Seeing the Complete Picture

Rounding out this linkz post is the article What It Looks Like: Malware Infection via a Weaponized Document by Harlan Carvey. Harlan obtained a weaponized document, executed it in a test system, and then walked through his examination to identify artifacts on the host. The document he obtained was already written about from the dynamic analysis perspective but it didn't address artifacts left on the system. The thing I really liked about Harlan's post is it addresses an area that very little is written about. There are a ton of articles about dynamic analysis and offensive techniques such as exploiting a vulnerability but there is not as much about attack vector artifacts left on the system. The attack vector artifacts showing how it looks when a hacker (or cracker) uses a path or means to gain access to a computer or network server in order to deliver a payload or malicious outcome. Over the past month there have been various articles mentioning the increase in malicious documents being used to compromise systems. The malicious documents mentioned vary as well as their payloads vary. However, the activity left on the system due to a malicious document will remain the same. This activity is what Harlan addressed in his post and the information helps to bring a more complete picture into view. Harlan also provided his thoughts on a few take-aways for detection and response.
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Triaging a System Infected with Poweliks

Sunday, January 4, 2015 Posted by Corey Harrell 3 comments
Change is one of the only constants in incident response. In time most things will change; technology, tools, processes, and techniques all eventually change. The change is not only limited to the things we rely on to be the last line of defense for our organizations and/or customers. The threats we are protecting them against change too. One recent example is the Angler exploit kit incorporating fileless malware. Malware that never hits the hard drive is not new but this change is pretty significant. An exploit kit is using the technique so the impact is more far reaching than the previous instances where fileless malware has been used (to my knowledge.) In this post I'm walking through the process one can use to triage a system potentially impacted by fileless malware. The post is focused on Poweliks but the process applies to any fileless malware.

Background on Why This Matters

In my RSS feeds, I was following the various articles about how an exploit kit incorporated the use of fileless malware. The malware never gets dropped to the disk and gets loaded directly into memory. A few of the articles I'm referring to are: Poweliks: The file-less little malware that could, Angler EK : now capable of "fileless" infection (memory malware), Fileless Infections from Exploit Kit: An Overview, POWELIKS: Malware Hides In Windows Registry, and POWELIKS Levels Up With New Autostart Mechanism. Reading the articles made one thing clear: one of the most effective tools to deliver malware (exploit kits) is now using malware that stays in memory.

This change has a significant impact on multiple areas. If the malware stays in memory then the typically artifacts we see on the host will not be there. For example, when the malware is loaded into memory then it won't create program execution artifacts on the system. This means the triage and examination process needs to adjust. As I mentioned previously, this change was implemented into a widely known exploit kit (Angler exploit kit.) The systems infected with this exploit kit can be far reaching. This means we will encounter this change sooner rather than later; if you haven't faced it already. Case in point, recently the Internet Systems Consortium website was compromised and was redirecting visitors to the Angler exploit kit. The last impact is if this change provides better results for the people behind it then I can see other exploit kit authors following suit. This means fileless malware may become even more widespread and it's something that is here to stay.

I knew memory forensics is one technique we can use to find the malware in memory. (if you need a great reference on how to do this check out the book the Art of Memory Forensics.) However, the question remained what does this look like. I took the short route for a quick answer to my question by reaching out to my Twitter followers. I asked them the following: "Anyone know how Poweliks code looks from memory forensics perspective?"

The first responses I got back was from Adam over at the Hexacron blog (great blog by the way) as shown below.

Adam provided some great information; to narrow in on the dllhost.exe process and what strings to look for. Another response I got was from @lstaPee as shown below:

@lstaPee provided a few more tidbits. RunDll32.exe injects code into the Dllhost.exe and dllhost.exe should have network connections. The response I got back from Twitter was great but I really needed to address the bigger question. If and when I have to triage a system infected with Poweliks what is the fastest way to perform the triage to locate the malware and determine the root cause of the infection. A question I needed to dig in to in order to find out the answer.

Testing Environment

As much as I wanted to simulate this attack by finding a live link to an Angler exploit kit I knew it would be very difficult. Based on various articles I read, Angler is VMware aware and  it doesn't always deliverer the fileless malware. I opted to use a Powelik's dropper/downloader. I used the sample MD5 0181850239cd26b8fb8b72afb0e95eac I found on Malwr. The test system was a Windows 7 32bit virtual machine in VMware.

The test conditions were really basic. I executed the sample by clicking it and then waited for about a minute. The VM was suspended and I collected the memory and prefetch files. I then unsuspended the VM followed by rebooting the system. After reboot, I logged onto the VM and then suspended it to collect the memory and prefetch files.

My tests was to analyze the Poweliks infection from two angles. The initial infection prior to a system reboot and a persistent infection after the system reboots. My analysis had one exception. By clicking the Poweliks executable to infect the system this action created program execution artifacts. I ignored these artifacts since they wouldn't be present if the malware was loaded directly into memory. I followed my typical examination process on the memory images and vmdk files but this post only highlights the activity that directly points to Poweliks. There was other activity of interest but the activity by itself does not indicate anything malicious. This activity I opted to omit from the post.

Poweliks' Behavior

Before diving into the triage process and what to look for it's important I discuss one Poweliks' behavior. I won't go into any details how I first picked up on this but I will show the end result. What the behavior is and how it can help when triaging Poweliks specifically. The screenshot below shows partial of the Malwr's behavior analysis section showing the behavior I'm referring to.

Upon a system's initial infection, the malware calls rundll32.exe which then calls powershell.exe who injects code into the dllhost.exe process. In the image above the numbers are for the process IDs and this relevant as we dig deeper into the behavior.

The image below shows activity that occurs shortly after the rundll32.exe process starts. As can be seen, rundll32.exe attempts to load a module into its own address space with the LdrLoadDll function. The module being loaded is actually javascript; this behavior is well documented for Poweliks such as in the article Poweliks – Command Line Confusion. Notice the activity following the LdrLoadDll function call is trying to locate the address for the RunHTMLApplication function. Here's the keyword Adam pointed out.

The images below shows activity that occurs just prior to powershell.exe process exiting. Powershell.exe creates the dllhost.exe process in the suspended state. Code gets injected into this suspended dllhost.exe process and then it is resumed. This technique is process hollowing and when the suspended process is resumed it executes the injected code.

Triaging System Infected with Poweliks

Triage is the assessment of a security event to determine if there is a security incident, its priority, and the need for escalation. As it relates to potential malware incidents, the purpose of triaging may vary. In this instance, triage is being used to determine if an event is a security incident or false positive by identifying  malware on the system. Confirming the presence of malware allows for a deeper examination to be completed. The triage process I'm outlining is to confirm the presence of the Poweliks fileless malware.

Triaging with Host Artifacts

Normally, triaging a system using artifacts on the host is an effective technique to identify malware. This is especially true when leveraging program execution artifacts. However, loading malware directly into memory has a significant impact on the artifacts available on the host. There are very little artifacts available and if the malware doesn't remain persistent then there will be even less. Triaging a system infected with Poweliks is no different. Most of the typically artifacts are missing but it can still be identified using prefetch files and autorun locations.

Prefetch Files

Previously I outlined the Poweliks behavior where the rundll32.exe process runs, which then starts a powershell.exe process before injecting code into the dllhost.exe suspended process. This behavior is apparent in the prefetch files at the point of the initial infection. The image below shows the activity.

The prefetch files show the sequence of rundll32.exe executing followed by powershell.exe before dllhost.exe. Furthermore, the dllhost.exe prefetch file is missing the process path. The missing process path indicates process hollowing was used as I outlined in the post Prefetch File Meet Process Hollowing. The prefetch files contain references to files accessed during the first 10 seconds of application startup. The dllhost.exe prefetch file contains revealing ones. It contains a reference to wininet.dll for interacting with the network and files associated with Internet Explorer as shown below.

This specific prefetch file sequence only occurs upon the initial infection. Future system restarts where Poweliks is loaded into the dllhost.exe process only shows the dllhost.exe prefetch file. The file references in this prefetch still show references to files located in the user profile.


The prefetch files contain a distinctive pattern indicating a Poweliks infection. Depending on the sample, autoruns can reveal even more. I mention depending on the sample because Poweliks has changed its persistence mechanism. Initially it used the Run registry key before moving on to a CLSID registry key. I thought one article mentioned Poweliks may not try to remain persistent at all times. If Poweliks does try to remain persistent then its mechanism can be used to find it. Keep in mind, Poweliks has taken self protection measures to prevent this mechanism from being located on a live system. The easiest method to bypass these measures is to access the system remotely with a forensic tool like Encase Enterprise, mount the drive, and then run Regripper across the hives.

The image below shows the Run key from the user account on my test system. The sample I used was older since the Run key was used but it still is a tell-tale sign for a Poweliks infection.


Memory Analysis Triage

Fileless malware may leave very little artifacts available on the host's hard drive but it still has to reside in memory. The most effective technique to identify a fileless malware infection is memory forensics. A Poweliks infection is not an exception since it stands out in memory whether if the memory is examined after the initial infection or a system reboot.

Network Connections

One area with malware indications is network activity are for unusual processes. @lstaPee alluded to this in their tweet about Poweliks. The Volatility netscan plug-in does show network activity for  the dllhost.exe process involving the IP address on port 80 for HTTP traffic. dllhost.exe is not a process typically associated with web traffic so this makes it a good indicator pointing to Poweliks.

Process Listing

Another area with malware indications is the process listing showing unusual ones or ones with unusual commands. The Volatility pslist, psscan, and pstree -v plugins did not reveal anything that could definitely be used as an indicator but they did show the dllhost.exe process running. I checked a few clean systems to see if dllhost.exe normally runs but the process was not running by default.  This doesn't mean it can be used as an indicator because there could be other reasons for dllhost.exe running besides Poweliks. The screen below is from the pstree plug-in showing the command-line for launching dllhost.exe (notice there are no other options used in the command.)

Injected Code

Looking for processes with injected code is an effective technique to locate malware on a system. This is the one technique that absolutely reveals Poweliks on a system. The Volatility malfind plug-in showed the dllhost.exe process with injected code. This matches up to the articles about the malware and behavior analysis showing code does get injected into the dllhost.exe process. The image below shows the partial output from malfind.

Extracting the injected code and scanning it with antivirus confirms it is Poweliks. The image below shows the VirusTotal results for the injected code. Microsoft detected the code as Trojan:Win32/Powessere.A which is their classification for Poweliks.


The last area containing indicators pointing to Poweliks are the strings in the dllhost.exe process. The method to review the strings is not as straight forward as running a single Volatility plug-in. The strings command reference walks through the process and it's the one I used. The only thing I did different was to grep for my process ID to make the strings easier to review. The dllhost.exe strings revealed URLs such as one containing the IP address found with the netscan plug-in.

The most significant string found was the command used to make rundll32.exe inject code into the dllhost.exe process as shown below. The presence of this string alone in the dllhost.exe process indicates the system is infected with Poweliks.

Wrapping Things Up

The change introduce by the Angler exploit kit creator(s) is causing us to make adjustments in our processes. The effective techniques we used in the past may not be as effective against fileless malware. However, it doesn't mean nothing is effective preventing us from triaging these systems. It only means we need to use other processes, techniques, and tools we have at our disposal. We need to take what artifacts do remain and use it to our advantage. This post was specific to the Poweliks malware but the techniques discussed will apply to other fileless malware. The only difference will be what data is actually found in the artifacts.

The Art of Memory Forensics Book Review

Sunday, December 28, 2014 Posted by Corey Harrell 6 comments
Christmas is in the rear view mirror and you may be left wondering about the gift you didn't find under the tree. The gift loaded with DFIR goodness to bring you into the new year. A gift you can use to improve your knowledge and skills. A gift to help you get to the next level in digital forensics, incident response, or malware analysis. You didn't get any DFIR goodness so it's a great opportunity to reward yourself with a gift of your own choice; one to accomplish what the previous sentences alluded to. If you fit this description then the book The Art of Memory Forensics is what you should be looking for. Even if the description doesn't fit and you don't already own this book then you should seriously check it out. This post is my review of the book The Art of Memory Forensics.

Three in One

The book addresses memory forensics on the following three operating systems: Windows, Linux, and Mac. This makes it an outstanding book since it addresses the most commonly faced operating systems. Furthermore, the content not only addresses memory forensic techniques but goes into detail about operating system internals. The majority of the systems I encounter are Windows systems so my focus was on the Windows portion of the book. (I did skim the other sections but I took my time in the Windows section.) The content went deep into the various Windows data structures and function calls. This makes the book an outstanding reference to better understand operating system internals. I easily envision myself using this book as a reference for years to come.

Not Just Words but Hands-on

One thing I tend to look for in a technical security book is how easy is it for the reader to take the content/techniques then apply it elsewhere. This is another area where the Art of Memory Forensics shines. The book's website provides additional materials that accompany the book. The items include lab questions, lab answers, and memory images for each chapter. This allows the reader an opportunity to do the hands-on labs to re-enforce that chapter's content. It's a great way to learn since you are actually performing memory forensics on an image after reading about it. Furthermore, to explain concepts the book uses - for the most part- memory images freely available on the Internet. As you read the book you can follow along by performing the same activities on the same memory images. At times the authors don't explicitly say what memory image they are using but the name of the memory images is pretty revealing. For example, in the Detecting Registry Persistence section (Kindle version page 4626) the Volatility handles plug-in is ran against a memory image named "laqma.mem". On the SampleMemoryImages webpage you can see a Laqma memory image is available and this is the one used in the book. This occurs frequently in the book as well as the authors specifically mentioning the memory image they are using.

The one area I thought that could make this book even better would be for the authors to explicitly state the memory image being used in the examples. This would make it easier for others (especially people who are not aware about the available memory images) to follow along in the book doing the same examples.

Memory Forensics in Toolbox

The last point I wanted to touch on about why I think so highly of this book is memory forensics is a process we need to have in our toolbox. This is true regardless if the work involves incident response or malware analysis. In incident response, there are times when you need to examine the volatile data on a system to obtain an answer. For example, a system is making network connections to a known malicious domain, which is setting off alerts. To tie the network connections to an actual process on the system requires memory forensics. The need for this in incident response is even more so with the recent increase of an exploit kit leveraging fileless malware. In malware analysis, there are times when memory forensics can provide additional information about a sample under examination. Does it open a socket, make network connections, inject code, hook functions, etc.. Memory forensics is now a process we need available in our toolbox and this book can help put it there.

All in All

If you are looking for a gift loaded with DFIR goodness, looking to improve your knowledge/skills, or looking for help to get to the next level in DFIR then this book is for you. The Art of Memory Forensics is a hefty book loaded with excellent content. It's an outstanding book and for those who don't already own it should seriously consider making it their next DFIR purchase. Just make sure to get your money's worth by grabbing the labs, memory images, and then putting hands to the keyboard as you read along.

Prefetch File Meet Process Hollowing

Wednesday, December 17, 2014 Posted by Corey Harrell 4 comments
There are times when you are doing research and you notice certain behavior. You may had been aware about the behavior but you never consider the impact it has on other artifacts we depend on during our digital forensic and incident response examinations. After thinking about and researching the behavior and impact, it makes complete sense; so much so it's pretty obvious after the fact. In this post I'm exploring one such behavior and its impact I came across researching systems impacted by the Poweliks fileless malware. Specifically, how creating a suspended process and injecting code into it impacts the process's prefetch file.

The statement below is the short version describing the impact injecting code into a suspended process has on its prefetch file. For those wanting the details behind it the rest of the post explains it.

If the CreateProcess function creates a process in the suspended state and code gets injected into the process. The prefetch file for that process will contain the trace for the injected code and not the original process. Therefore, the prefetch file can be an indicator showing this technique was used.

Process Hollowing Technique

Malware uses various techniques to covertly execute code on systems. One such technique is process hollowing, which is also known as process replacement. The book Practical Malware Analysis states the following in regards to this technique:

"Process replacement is used when a malware author wants to disguise malware as a legitimate process, without the risk of crashing a process through the use of process injection.

Key to process replacement is creating a process in a suspended state. This means that the process will be loaded into memory, but the primary thread of the process is suspended. The program will not do anything until an external program resumes the primary thread, causing the program to start running"

In addition, the book The Art of Memory Forensics states the following:

"A malicious process starts a new instance of a legitimate process (such as lsass.exe) in suspended mode. Before resuming it, the executable section( s) are freed and reallocated with malicious code."

In essence, process hollowing is when a process is started in the suspended state, code is injected into the process to overwrite the original data, and when the process is resumed the injected code is executed. In a future post I will go into greater detail about this technique but for this post I wanted to keep the description at a high level.

Windows Internals Information

To fully explore the process hollowing behavior on a Windows system and its impact on the prefetch file it is necessary to understand Windows internals. Specifically, when and why prefetch files are created  and how processes are created.

Windows Prefetcher Information

Prefetch files are a well known and understood artifact within the DFIR field. These files are a byproduct of the Windows operating system trying to speed up either the boot process or applications startup. The book Windows Internals, Part 2: Covering Windows Server 2008 R2 and Windows 7 states the following:

"The prefetcher tries to speed the boot process and application startup by monitoring the data and code accessed by boot and application startups and using that information at the beginning of a subsequent boot or application startup to read in the code and data."

As it relates to application prefetch files the book continues by saying:

"The prefetcher monitors the first 10 seconds of application startup."

The information the prefetcher monitors is explained as follows:

"The trace assembled in the kernel notes faults taken on the NTFS master file table (MFT) metadata file (if the application accesses files or directories on NTFS volumes), on referenced files, and on referenced directories."

In essence, if the prefetcher is enabled on a Windows systems then the first 10 seconds of execution is monitored to determine what files and directories the application accesses. This information (or trace) is then recorded in a prefetch file located inside the C:\Windows\Prefetch directory.

Windows Flow of Process Creation

Knowing about process hollowing and prefetching is not enough. It's necessary to understand the flow of process creation in order to see the various activities that occur when a process is created. The book Windows Internals, Part 1: Covering Windows Server 2008 R2 and Windows 7 goes into great detail about process creation and below are the main stages:

1. Validate parameters; convert Windows subsystem flags and options to their native counterparts; parse, validate, and convert the attribute list to its native counterpart.

2. Open the image file (. exe) to be executed inside the process.

3. Create the Windows executive process object.

4. Create the initial thread (stack, context, and Windows executive thread object).

5. Perform post-creation, Windows-subsystem-specific process initialization.

6. Start execution of the initial thread (unless the CREATE_ SUSPENDED flag was specified).

7. In the context of the new process and thread, complete the initialization of the address space (such as load required DLLs) and begin execution of the program.

The picture below illustrates the process creation main stages:

The main stages highlight a very important point as it relates to process hollowing. When the a process is created it doesn't start executing until Stage 7. If the process is created in a suspended state then the first 6 stages are completed. The question is when does the prefetcher come into play. The book Windows Internals Part 1 states the following activity occurs in stage 7:

"Otherwise, the routine checks whether application prefetching is enabled on the system and, if so, calls the prefetcher (and Superfetch) to process the prefetch instruction file (if it exists) and prefetch pages referenced during the first 10 seconds the last time the process ran."

This is very important so it is worth repeating. The prefetcher monitoring application startup occurs in stage 7 when the application is executing. However, a process that is created in the suspended state does not execute until it is resumed. This means if the process hollowing technique is used then when the process resumes and executes the injected code the prefetcher is monitoring the files/directories accessed by the injected code and not the original process. In shorter words:

If the CreateProcess function creates a process in the suspended state and code gets injected into the process. The prefetch file for that process will contain the trace for the injected code and not the original process. Therefore, the prefetch file can be an indicator showing this technique was used.

Process Hollowing Prefetch File

It's always helpful to see what is being described in actual data to make it easier to how it applies to our examinations. To generate a prefetch file I double-clicked the svchost.exe executable located in the C:\Windows\Prefetch directory. Below is the partial output from this prefetch file being parsed with Harlan Carvey's script in the WFA 4th edition book materials. (One note about the prefetch file; I added the underscore at the end to force the creation of a new prefetch file.)

File     : C:\Prefetch\
Last Run : Wed Dec 17 20:58:57 2014
Run Count: 1

Module paths:

As shown above, the svchost.exe executed one time and some of the files accessed are reflected in the module paths section. I asked Harlan about where the executable path comes from in prefetch parsers since the prefetch file format does not record the executable path. He confirmed what I was assuming. Prefetch parsers search the module paths for the name of the executable referenced at offset 0x0010.

Now let's take a look at the prefetch file for a svchost.exe process that was hollowed out. The Lab12-02.exe executable provided with Practical Malware Analysis performs process hollowing to the svchost.exe process. This can be seen performing dynamic analysis on the executable. The images below are from the executable being ran in Malwr.

Lab12-02.exe first creates the svchost.exe process in the suspended state. Notice the creation flag of 0x00000004. Also, make note about the process handle to the suspended process (0x00000094).

Lab12-02.exe then continues by injecting code into the suspended svchost.exe process.

Lab12-02.exe finishes injecting code into the suspended svchost.exe process with the process handle 0x00000094 before it resumes the suspended process.

Below is the partial output from this prefetch file being parsed with Harlan's script.

File     : C:\ Prefetch\
Exe Path :
Last Run : Wed Dec 17 20:59:48 2014
Run Count: 1

Module paths:

It may not be obvious in the partial output but the files accessed by the injected code is different than the normal svchost.exe process. One of the more obvious files is what is not accessed; the original executable itself. Notice how the executable path contains the name of the prefetch file and this is due to the actual svchost.exe process not being accessed within 10 seconds of the injected code running.

Circling Back To Poweliks

I mentioned previously that I noticed this behavior when researching the Poweliks fileless malware. This malware doesn't write its binary to disk since it stays in memory. The malware is not only not on the hard drive but other typical artifacts may not be present as well (such as the normal program execution artifacts.) In the near future I'll have a detailed post about how to triage systems impacted by this malware but I wanted highlight why the information I shared in this post matters. The screenshot below shows parsed prefetch files from a test system infected with a Poweliks dropper. My only clue to you is: one prefetch file is not like the others?

There is one dllhost.exe prefetch file that has the missing process path. A closer inspection of this prefetch file reveals some other interesting file access during application start-up:

During access start-up files associated with Internet activity were accessed in addition to the WININET.DLL dll for making HTTP requests. When Poweliks (or at least the samples I've reviewed) initially infects a computer it performs the following actions: rundll32.exe process starts the powershell.exe process  that then starts a suspended dllhost.exe and injects code into it. Powershell.exe then resumes the dllhost.exe process that executes the Poweliks malicious code. The screenhots above illustrate the behavior of process hollowing performed by Poweliks and the impact on the dllhost.exe prefetch file.

The above indication of the missing executable path in the dllhost.exe prefetch file  is only for the initial infection when process hollowing is used. (The malicious code doesn't access the file it injects in once it executes) If Poweliks remains persistent and the system reboots the malicious code is still injected into dllhost.exe process but it doesn't appear to be process hollowing. These dllhost.exe prefetch files will contain the dllhost.exe executable path; along with the trace for suspicious file access as shown in the last screenshot. This is reflected in the second dllhost.exe prefetch file highlighted in the above screenshot.


Uncovering behaviors during research is helpful to put something you take for granted in a different perspective. Process hollowing behaves in a specific way in the Windows operating system and it can impact prefetch files in a specific way. This impact can be used as an indicator to help explain what occurred on a system but it needs context. A missing process executable in a prefetch file does not mean process hollowing occurred. However, a missing process executable along with suspicious file access during application start-up and an indication a system was compromised means something completely else. 

The Hammer Is Not Broken

Sunday, November 23, 2014 Posted by Corey Harrell 2 comments
I went to my local hardware store to buy one of the latest hammers. I brought the hammer home but it was unable to build the shed in my backyard. I spoke to someone else who said something similar. They bought the hammer and it didn't build what they wanted it to do. The expectation was that the hammer should do what it needs to do automatically and if it doesn't then the hammer is broken. It doesn't live up to its expectations, it wasn't the best investment, and the hammer developers need to start over.

Every now and then there are articles about how a certain security technology is broken. The recent focus of criticism is SIEM technology. It's broken because it doesn't do everything automatically and live up to peoples' expectations. The expectation that the technology should be able to be implemented and then automatically solve problems. Similar, to the expectation of a shed being built by simply buying a hammer. The hammer is not at fault; similar to the security technology not being at fault. Both of them are tools and the issue is with who is wielding that tool.

The hammer is not broken. The security technology is not broken. What is broken is the person (or organization) holding the tool. They need the critical thinking and problem solving skills to make the tool do what it needs to do and meet expectations along the way.

"analysts can be trained to use a tool in a rudimen-tary manner, they cannot be trained in the mind-set or critical thinking skills needed to master the tool"

                                                                               ~ Carson Zimmerman

The issue is not with the tool. The issue is the organization hasn't put the tool in the right peoples' hands and until they do the brokenness won't be fixed.