Monday, January 17, 2022

Registry Analysis - The "Why"

Why is Registry analysis important?
The Windows Registry, in part, controls a good bit of the functionality of a Windows system. As such, Registry analysis can help you understand why you're seeing something, or why you're not seeing something, as the case may be.

For example, Registry "settings" (i.e., keys, values, or combinations) can be/have been used to disable Windows Event Logs, enable or disable auditing (the content that goes into the Windows Event Log), disable access to security tools, enable or disable other functionality on Windows systems, etc. The Registry can be used to enable or disable application prefetching, which produces artifacts very commonly used by forensic analysts and incident responders. 

Registry values and data can provide insight into what an analyst is seeing, or why they're not seeing something they expect to see. For example, adding a specific Registry key to the System hive effectively disables logging to the Security Event Log; why clear the log when you can simply stop the event records from being written? Not seeing application prefetching files being generated on a Windows 10 or 11 system? Well, there's a Registry value for that, as well! 

Most analysts are aware that, particularly with respect to the file system, something "deleted" isn't always "gone". This is true for files, but even more so for records (elements with a file), and it's also true for the Registry. However, the Registry can be used to disable functionality the prevents activity from being recorded in the first place. As such, the records are never actually generated, and therefore, cannot be recovered. This is an important distinction to make, as over the past decade and a half, we've seen threat actors actively modify systems within an infrastructure to suit their own needs. For example, disabling or removing security tools, modifying operating system capabilities, and enabling or disabling functionality; whether manually or via a batch file (or some other means), many of these modifications manifest themselves as changes in the Registry. 

Case in point; in the spring of 2019, I was working with incident responders to track activities associated with the Ryuk ransomware group. Looking back to Sept, 2018, we'd seen where the actors had run mimikatz, and then within seconds, moved laterally. Closer examination showed that the actor had modified the Registry so that the operating system would maintain credentials in memory in plain text 6 to 9 days prior to running mimikatz. That way, they didn't have to copy the hashes so that they could crack them; the credentials were already in plain text, so all they had to do was choose the account with the highest level of privileges and move to subsequent systems. This is just one example of how threat actors have modified systems within a compromised infrastructure to meet their needs.

User Activity
In addition to "current state" configuration settings, the Registry "tracks" or maintains a history of activity on the system; updates, upgrades, devices connected, etc. This is also true for user actions; files opened or interacted with, applications launched, WiFi networks connected to, etc.

There used to be a few law enforcement officers who'd contact with me with questions; "used to" because they've since retired. One in particular had worked out a process with me, where she'd share an NTUSER.DAT from an active case and I'd process the hive and give her a comprehensive, detailed list of files interacted with by the user. I'd include applications used, and if applicable, dates and times of the interactions. I'd provide her with a complete description of how this information was found, so that she could replicate my findings so that she could testify (if necessary). She'd then tie the file paths and names to specific files and content, and take that to the pre-trial conference, and very often, she'd end up with a plea agreement.

In 2005, Cory Altheide and I published the first paper to address tracking USB devices across Windows systems. At the time, we were working with Windows XP, and since then, the Windows operating system has grown considerably in the records generated when USB devices are connected, as well as differentiating between various protocols. For example, connecting a smartphone or digital camera to a Windows computer via a USB cable appears in a different manner from a USB thumb drive; connecting a smartphone or a digital camera to a computer can mean the difference between possession and production of illicit images. 

Of course, devices connected via USB doesn't address devices connected via Bluetooth, or Wifi networks to which the computer has been connected.

"Proof of Life", Intent, Sophistication
Information derived from analysis of the Windows Registry can be leveraged to demonstrate "liveness", or to put a suspect "behind the keyboard". In addition, the totality of information derived from Registry analysis can be used to further the understanding of a user or threat actor's intent (what they're after) and their level of sophistication. For example, Registry analysis can show use that the threat actor added an account to a system as a means of persistence, and then added the account to different groups so that the account could be used to access the system remotely via RDP. From there, we can see if the icon for the account was hidden from the Welcome Screen, as well as if additional means of persistence were added.

Also, the timing between the various modifications we observe, in addition to the modifications themselves, can be leveraged to determine attribution. We have observed, for example, some threat actors making use of batch files or VBS scripts to make Registry modifications, either directly via reg.exe, or indirectly via other native tools such as sc.exe, or schtasks.exe. The timing of the modifications, in relation to other modifications and system impacts, can be used to establish attribution; was this truly the threat group we suspect it to be, or someone else? Or, do the observables indicate an evolution of capabilities of the threat group?

We've also seen how RaaS providers embed dozens of preemptive commands in the executables they provide; in the spring of 2020, one RaaS sample contained 156 embedded commands to disable Windows services, via sc.exe and other means. Looking at the timing of the modifications that actually took effect (not all services may be active on the impacted system) alongside files being encrypted provides insight into attribution.

Eco-System
A good bit of what we can find in the Registry aren't things we find as a result of a threat actor or malware directly interacting with the Registry; rather, there are more than a few keys or values that are "indirect artifacts", in that they're generated as a result of the actor or malware's interaction with the "eco-system" (platform, OS, applications, etc.). A good example of this is the AppCompatCache, or "ShimCache"; the entries in the value data are not created as a result of malware directly writing to the value, but rather that the file was on the system and subject to an application compatibility check.

From a configuration perspective, Registry (specific key, value, and data) settings can result in the OS being configured to generate additional "evidence" or tracks as a result of interaction with the eco-system. For example, there are settings to enable additional LSA protections; essentially adding protection to the LSASS.exe process. Setting the capability and rebooting generates an event record (in the Windows Event Log), and then interacting with the process in an incorrect manner will also generate Windows Event Log records (in the appropriate log).

Registry Analysis
Registry analysis is not a stagnant thing. That is to say that you don't reach a point where you're "done", and don't have to go any further. You don't just reach a point in, say, 2018 where you say, "I'm done" and don't continue to evolve your analysis. This is due to the fact that, even in a corporate environment, it's extremely difficult to find two systems that are the same; that is, system "loads" or configurations (base operating system, applications, configurations, etc.) are often very different. As a DFIR consultant, I would encounter different basic loads and configurations with every client, and even within that client, systems had different applications installed (in part, due to mergers and acquisitions), were configured differently, etc. Even when there was a "common load", where every system was supposed to have some common configuration, they weren't; often times, the version of the application would be a rev or two behind others, hadn't been updated in some time, etc.

Also, analysis goals very often differ; what you're looking to prove or disprove will vary depending upon your investigative goals. Are you dealing with a malware infection, a data breach, an insider threat, corporate espionage, access to illicit images or materials, or something else entirely?

4 comments:

Anonymous said...

Another good post on registry analysis. Do you have any thoughts on Windows registry key/value auditing?

BTW what RegRipper plugin extracts information about the firewall these days? Sorry for the dumb question, but I don't see fw_config.pl on GitHub.

H. Carvey said...

> Do you have any thoughts on Windows registry key/value auditing?

Sure. Like anything else, it depends upon how it's set up, maintained, and monitored.

What's the point of generating audit logs if no one's monitoring them?

> ...what RegRipper plugin extracts information about the firewall these days?

What's the key for that these days?

Anonymous said...

> Sure. Like anything else, it depends upon how it's set up, maintained, and monitored.

True. Do you know of any high fidelity registry auditing you've had or seen success with? Anything other than maybe the Run keys?


> What's the key for that these days?

I think it should be Software\Policies\Microsoft\WindowsFirewall\

https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-gpfas/2efe0b76-7b4a-41ff-9050-1023f8196d16

I'll admit, the rules look way more complicated to parse than I was expecting.

H. Carvey said...

> ...high fidelity registry auditing...

I can't say I've done it, but there should be more than a few things you can audit...it all depends upon your infrastructure.

> I think it should be Software\Policies\Microsoft\WindowsFirewall\...

I think that's for GPOs set on the XP-style firewall...maybe. More recent versions of Windows use the SharedAccess services key:

https://www.technlg.net/windows/disable-enable-firewall-registry-key/