Using Real-Time Events in Investigations

Read the original article: Using Real-Time Events in Investigations

To understand what a threat actor did on a Windows system, analysts
often turn to the tried and true sources of historical endpoint
artifacts such as the Master File Table (MFT), registry hives, and
Application Compatibility Cache (AppCompat). However, these evidence
sources were not designed with detection or incident response in mind;
crucial details may be omitted or cleared through anti-forensic
methods. By looking at historical evidence alone, an analyst may not
see the full story.

Real-time events can be thought of as forensic artifacts
specifically designed for detection and incident response, implemented
through Enterprise Detection and Response (EDR) solutions or enhanced
logging implementations like Sysmon.
During active-attacker endpoint investigations, FireEye Mandiant
has found real-time events to be useful in filling in the gaps of what
an attacker did. These events record different types of system
activities such as process execution, file write activity, network
connections, and more.

During incident response engagements, Mandiant uses FireEye
Endpoint Security to track endpoint system events in real-time.
This feature allows investigators to track an attacker on any system
by alerting on and reviewing these real-time events. An analyst can
use our solution’s built-in Audit Viewer or Redline to review
real-time events.

Let’s look at some examples of Windows real-time events available on
our solution and how they can be leveraged during an investigation.
Let’s assume the account TEST-DOMAIN\BackupAdmin was an inactive
Administrator account compromised by an attacker. Please note the
examples provided in this post are based on real-time events observed
during engagements but have been recreated or altered to preserve
client confidentiality.

Process Execution Events

There are many historical process execution artifacts including AppCompat,
AmCache,
WMI
CCM_RecentlyUsedApps, and more.
A single artifact rarely covers all the useful details relating to a
process’s execution, but real-time process execution events change
that. Our solution’s real-time process execution events record
execution time, full process path, process identification number
(PID), parent process path, parent PID, user, command line arguments,
and even the process MD5 hash.

Table 1 provides an example of a real-time process execution event
recorded by our solution.

Field	Example
Timestamp (UTC)	2020-03-10 16:40:58.235
Sequence Number	2879512
PID	9392
Process Path	C:\Windows\Temp\legitservice.exe
Username	TEST-DOMAIN\BackupAdmin
Parent PID	9103
Parent Process Path	C:\Windows\System32\cmd.exe
EventType	Start
ProcessCmdLine	"C:\Windows\Temp\legitservice.exe" -b -m
Process MD5 Hash	a823bc31395539816e8e4664e884550f

Table 1: Example real-time process execution event

Based on this real-time process execution event, the process C:\Windows\System32\cmd.exe with PID 9103 executed
the file C:\Windows\Temp\legitservice.exe
with PID 9392 and the MD5 hash a823bc31395539816e8e4664e884550f. This new process
used the command line arguments -b -m under the user context of TEST-DOMAIN\BackupAdmin.

We can compare this real-time event with what an analyst might see
in other process execution artifacts. Table 2 provides an example
AppCompat entry for the same executed process. Note the recorded
timestamp is for the last modified time of the file, not the process
start time.

Field	Example
File Last Modified (UTC)	2020-03-07 23:48:09
File Path	C:\Windows\Temp\legitservice.exe
Executed Flag	TRUE

Table 2: Example AppCompat entry

Table 3 provides an example AmCache entry. Note the last modified
time of the registry key can usually be used to determine the process
start time and this artifact includes the SHA1 hash of the file.

Field	Example
Registry Key Last Modified (UTC)	2020-03-10 16:40:58
File Path	C:\Windows\Temp\legitservice.exe
File Sha1 Hash	2b2e04ab822ef34969b7d04642bae47385be425c

Table 3: Example AmCache entry

Table 4 provides an example Windows Event Log process creation
event. Note this artifact includes the PID in hexadecimal notation,
details about the parent process, and even a field for where the
process command line arguments should be. In this example the command
line arguments are not present because they are disabled
by default and Mandiant rarely sees this policy enabled by
clients on investigations.

Field	Example
Write Time (UTC)	2020-03-10 16:40:58
Log	Security
Source	Microsoft Windows security
EID	4688
Message	A new process has been created. Creator Subject: Security ID: TEST-DOMAIN\BackupAdmin Account Name: BackupAdmin Account Domain: TEST-DOMAIN Logon ID: 0x6D6AD Target Subject: Security ID: NULL SID Account Name: – Account Domain: – Logon ID: 0x0 Process Information: New Process ID: 0x24b0 New Process Name: C:\Windows\Temp\legitservice.exe Token Elevation Type: %%1938 Mandatory Label: Mandatory Label\Medium Mandatory Level Creator Process ID: 0x238f Creator Process Name: C:\Windows\System32\cmd.exe Process Command Line:

Table 4: Example Windows event log process
creation event

If we combine the evidence available in AmCache with a fully
detailed Windows Event Log process creation event, we could match the
evidence available in the real-time event except for a small
difference in file hash types.

File Write Events

An attacker may choose to modify or delete important evidence. If an
attacker uses a file shredding tool like Sysinternal’s SDelete, it is
unlikely the analyst will recover the original contents of the file.
Our solution’s real-time file write events are incredibly useful in
situations like this because they record the MD5 hash of the files
written and partial contents of the file. File write events also
record which process created or modified the file in question.

Table 5 provides an example of a real-time file write event recorded
by our solution.

Field	Example
Timestamp (UTC)	2020-03-10 16:42:59.956
Sequence Number	2884312
PID	9392
Process Path	C:\Windows\Temp\legitservice.exe
Username	TEST-DOMAIN\BackupAdmin
Device Path	\Device\HarddiskVolume2
File Path	C:\Windows\Temp\WindowsServiceNT.log
File MD5 Hash	30a82a8a864b6407baf9955822ded8f9
Num Bytes Seen Written	8
Size	658
Writes	4
Event reason	File closed
Closed	TRUE
Base64 Encoded Data At Lowest Offset	Q3JlYXRpbmcgJ1dpbmRvd3NTZXJ2aWNlTlQubG9nJy Bsb2dmaWxlIDogT0sNCm1pbWlrYXR6KGNvbW1hbmQ
Text At Lowest Offset	Creating ‘WindowsServiceNT.log’ logfile : OK….mimikatz(command

Table 5: Example real-time file write event

Based on this real-time file write event, the malicious executable
C:\Windows\Temp\legitservice.exe wrote the
file C:\Windows\Temp\WindowsServiceNT.log to
disk with the MD5 hash 30a82a8a864b6407baf9955822ded8f9. Since the
real-time event recorded the beginning of the written file, we can
determine the file likely contained Mimikatz credential harvester
output which Mandiant has observed commonly starts with OK….mimikatz.

If we investigate a little later, we’ll see a process creation event
for C:\Windows\Temp\taskassist.exe with the
MD5 file hash 2b5cb081721b8ba454713119be062491 followed by
several file write events for this process summarized in Table 6.

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