6 minute read

Event logs are a great way to detect adversary activity on a windows machine and be able to tell the story of what and how it happened.
Unfortunately, there are many event logs and not all of them are useful. Going through these logs can be daunting and requires keen eyes.
In this blog post, we will see what event logs are more useful than others and how we can utilize them.

Windows Event Log Structure
Windows event log provides information about hardware and software events occurring on a Windows operating system.
Windows event logs are stored under:
C:\Windows\System32\winevt\Logs

Events are written to event log channels and each event has an event ID.

Common channels are:
• Security
• System
• Application

There are 4 channel types:

Common
• Administrative
• Operational

Uncommon
• Debug
• Analytic

Now that you understand the basics let’s dive into the events.

Logon

Adversaries will steal your credentials and reuse them.
You will commonly see ids 4624 and 4634, successful logon and logoff.
These events have a field called logon ID. If a logon and logoff event have the same logon ID you can determine the session length.

When looking at 4624 events it’s vital that you whitelist built-in DWM and UMFD (Desktop Windows Manager & Usermode Font Driver) logons, this will considerably decrease the noise.

  • A large number of failed logons which is 4625 show brute force activity.
  • A large number of successful logons indicate lateral movement activity.

When other credentials are used for different tasks like process creation, network share, RDP, etc. event 4648 records them.
Using 4672 and 4624 you can detect user logons with admin-level privileges. When monitoring these events you should whitelist built-in windows accounts like SYSTEM. If adversaries create new accounts, event 4720 will detect this.

The logon event has a field called logon type, this field indicates how the logon occurred.
To understand the various ways you can log in to a system, use Microsoft’s official documents:
https://docs.microsoft.com/en-us/windows-server/identity/securing-privileged-access/reference-tools-logon-types

Summary:
4624: Logon
4625: Failed Logon
4634,4647: Successful Logoff
4672: Account logon with superuser rights (special logon)
4720: An account was created
4726: An account was deleted
4648: Logon using explicit credentials

Groups

Adversaries might add accounts to groups with administrative access. You can use these events to monitor the groups.

Summary:
4728: A member was added to a security-enabled global group
4732: A member was added to a security-enabled local group
4756: A member was added to a security-enabled universal group

Account Logon

Your first question might be “what’s the difference between account logon and logon?”
Logon refers to local login activity that occurs on the local system hence the log will be generated on the local system.
Account Logon refers to third-party authentication. In an enterprise domain users authenticate to the domain controller because of that you will generate logs on the DC and the local system.
If you login using a local account Account Logon events will be generated on the local system.

In an enterprise environment, you will have two types of authentication: NTLM and Kerberos.
Pass the hash (PtH) is a common technique that adversaries use which uses NTLM. In this case, event 4776 will be seen along with 4624 type 9 or 3, 4648, and 4672.
If Kerberos is the only method of authentication adversaries can utilize OverPass the hash by directly sending the RC4 or AES hashes, this will generate 4768, 4769, and 4771 along with 4624, 4648, and 4672.

Summary:
4776: The computer attempted to validate the credentials for an account
4768: A Kerberos authentication ticket (TGT) was requested
4769: A Kerberos service ticket was requested
4771: Kerberos pre-authentication failed

Enumeration

These events were added with Windows 10. They allow you to detect reconnaissance activity in the network. You will need to whitelist mmc, services, taskhostw, and explorer.
PowerView and Bloodhound are tools that adversaries use to enumerate your privileged users and groups.
You can use these events to detect who is running what process to enumerate your privileged users and groups.

Summary:
4798: A user’s local group membership was enumerated
4799: A security-enabled local group membership was enumerated

RDP

There are various ways for adversaries to move in your environment, including RDP.
RDP generates session reconnect 4778 and session disconnect 4779 events. But that’s not all, normal logon 4624 types 7 and 10 are also related to RDP.
It is important to emphasize that 4778 does not record new connections, only reconnects.
I should also mention that other channels record RDP activity too.

Summary:
4778: A session was reconnected to a Window Station
4779: A session was disconnected from a Window Station

Processes

At some point, adversaries will run their malware which will trigger 4688 (process creation) and 4689 (process exit).
Event 4688 can also capture the command line related to the process.

Summary:
4688: A new process has been created
4689: A process has exited

Network Share

Network shares can be used to mount shares like C$, ADMIN$, and IPC$ to move in the environment laterally.
When a share is accessed 5140 will be recorded, but this may not contain all the information you desire so you can use the much more verbose event 5145.

Summary:
5140: Network share was accessed
5145: Shared object accessed

Scheduled Tasks

Persistence is very important to adversaries and scheduled tasks are one way they maintain persistence.
When an adversary creates a new scheduled task 4698 and 106 will trigger.

Summary:
4698: Scheduled Task Created
4699: Scheduled Task Deleted
4700: Scheduled Task Enabled
4701: Scheduled Task Disabled
4702: Scheduled Task Updated

You can also look into the Task Scheduler channel for:
106: Scheduled Task Created
140: Scheduled Task Updated
141: Scheduled Task Deleted
200: Scheduled Task Executed
201: Scheduled Task Completed

Services

Services can be heavily targeted by adversaries for different purposes.
If an adversary breaks a service when exploiting it, event 7034 will trigger.
If adversaries use services for persistence and install a new service, events 7045 and 4697 will record it.

Summary:
7034: Service crashed
4697: A new service was installed on the system
7045: A new service was installed on the system
7040: Start type changed
7036: Service started or stopped

Powershell

Powershell is a great built-in tool for adversaries to use in our networks and because we can’t block access to it, PowerShell v5 comes with different logging capabilities.
Adversaries commonly use obfuscation with Powershell to evade security products. Script block logging will record it and it might automatically decode it as well.

Summary:
4103: Module Logging
4104: Scriptblock Logging

WMI

If you have been targeted by Tural or APT29 you will understand that WMI, just like Powershell, gives you access to do many things.
Adversaries will use the ConsumerFilter binding to achieve their goal. For this to happen they need to create a consumer, and a filter, and bind them together.
When going through these steps various event logs will record their action but at the end, 5861 will give you the best view of the actions that have occurred.

Summary:
5857: WMI Activity was detected
5858: WMI errors detected
5859,5860: WMI Filter/Consumer activity was detected
5861: WMI FilterConsumer Binding was detected

Removable Devices

These events allow you to track rogue BYODs, internal users exfiltrating sensitive data, and adversaries physically attacking your environment.

Summary:
4663: An attempt was made to access an object
4656: A handle to an object was requested
6416: A new external device was recognized by the System

Log Clearing

Legitimate log clearing can happen but it can be part of your baseline. Seeing logs being cleared at random times should be investigated using 1102 and 104.

Summary:
1102: The audit log was cleared

Under the System channel look for:
104: The audit log was cleared

Conclusion

While this is not an exhaustive list of all the events, it can be an amazing starting point for you to learn about the event logs and become more comfortable with them.
After you become familiar with these events it should be much simpler to expand your knowledge of event logs and find order amongst the chaos.