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Why you need to log and audit Windows events

In 2019, it was reported that the Windows operating system was used on 72.1 percent of the servers worldwide. Most organizations today are predominantly Windows shop.

Windows auditing and log monitoring becomes inevitable when you want to ensure and maintain the cybersecurity posture of your network. However, this is often easier said than done.

In this vital resource, we'll elaborate on what you need to know about Windows auditing, including from login to what information you need to obtain from the logs, and how you can correlate the log details with other activities on your network to gain a holistic view of your security posture.

The basic Windows auditing policy specifies a set of security-related activities for evaluating critical events. In Windows, by default, the logging and auditing of events are disabled, but this auditing policy allows you to enable logging of certain events to gain visibility into the most common security activities happening in your network.

The following events are covered under the nine basic security auditing policies:

• 1. Account logon events
• 2. Account management
• 3. Directory services
• 4. Logon events
• 5. Object access
• 6. Policy changes
• 7. Privilege use
• 8. Process tracking
• 9. System events

From the different events suggested, you can enable auditing for specific events depending on the security needs of your organization. We’ve curated some of the basic events and mapped them with the use case it can resolve.

1. Events to look to uncover attackers within network

Intruders and impostors want to stay inside the network unnoticed. They try to cover up traces of their malicious operations and lateral movements. However, if you monitor closely, you can differentiate the trace deletions from legit actions. We recommend you enable auditing for these events and inspect them regularly to uncover threat actors in your network:

i. Audit log clearance

Look for the user account from which the logs were cleared. Gathering and investigating all the activities done by that user account will add more contextual data to evaluate the audit log clearance and help you determine if it's a legitimate activity or not.

ii. Shutting down the logging service

Unless this is a planned event for maintenance, it can indicate a possible cyberattack.

2. Monitoring unusual login activity

Monitoring login activities can provide information on the anomalous activities happening within the network. For instance, User A logging in after work hours and trying to access protected information is subject to investigation. Multiple logins from the same account, a large number of login failures, and account lockouts are all common examples of unusual account activities. To monitor the login activities, enable auditing for these events:

i. Successful logons

The mode of logging in can give you clues to check the legitimacy of the attempt.

Monitor the Logon Type field for categories 3, 4, 5, 8, 9, and 10.

• 3 - Network: The user has logged in to the computer from somewhere else within the network.
• 4 - Batch: A process might be configured to execute on behalf of the user.
• 5 - Service: A service can be used to perform the login process.
• 8 - Network Clear Text: Transferring passwords in clear text format is dangerous as it could be sniffed to reveal. Avoid this logon type by protecting your network connection using encryption protocols like SSL/TLS or using VPN.
• 9 - New credentials: The user could have used different credentials to access any sensitive areas or execute admin-level commands (Runas) on the computer.
• 10 - Remote Interactive: Indicates that the logon was through Terminal Services or Remote Desktop. Could be a sign of lateral movement.

ii. Failing to log in

This event id is generated after every failed attempt regardless of the logon type. So you can easily check the type of logon used to access the system or resources. A massive spike in failure events within a short span may indicate a possible brute-force attack.

iii. Account lockouts

This happens when the user or attackers uses too many wrong passwords. Such events should always be followed up to check if it was legitimate.

3. Discover malicious registry changes

Attackers may try to modify the registry values to launch a malicious application or service during system startup. They can sometimes replace a whole registry or a particular key value in it to achieve this. One such example is the password filter DLL attack, where the hacker injects a malicious DLL file in the HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Control\ Lsa -> Notification Packages registry.

Monitoring registry changes lets you:

• 1. Capture unauthorized users or applications that change registry values.
• 2. Closely track privileged users registry activities to uncover privilege abuse and prevent malicious actions.
• 3. Ensure spot malware activity or suspicious changes to key registry values.

Here's a critical registry change event that you need to enable and monitor:

i. Registry value modification

Enable registry auditing and alerting on systems containing high-value data, domain controllers, and servers. Take regular backups of the registries in case anything goes wrong.

4. Detecting a possible brute-force attack

Brute force is a technique used by adversaries trying to input hundreds and thousands of username and password combinations within a short period, hoping to get one right. There are lots of tools to automate this process. With the help of these Windows events, you can perform basic brute force attack detection.

i. Multiple login failures

To spot brute-force attacks, look for multiple logon failures within a short period, and at least one successful logon from the same source.

ii. Account lockout

This happens when the user or attackers uses too many wrong passwords.

5. Watch out for file and folder activities

When adversaries gain access to your network, they want to drop malware packages like ransomware, or exfiltrate sensitive data and sell it on the dark web. A sudden spike in access requests to certain databases may indicate a potential breach. These are some of the events that you must log and audit to spot suspicious file and folder changes:

i. Attempting to access objects

This event id is generated when an object is accessed. The object can be a file, kernel system, registries, or files present on a removable disk. It is recommended that you set alerts to determine if anyone tries to access any object in protected servers.

6. Watch out inbound and outbound connections

Monitoring the traffic from and to the network adds contextual information to your threat hunting process. Connection details available in log data such as the source IP address and its location provide clear visibility of what's happening in your network when trying to detect security threats or attack attempts. When this information is correlated with other events, it helps you to identify the compromised systems, lateral movement of adversaries, malicious packages that are dropped into your network, and more. Therefore, it becomes essential for you to log and closely monitor the inbound and outbound connections. These are some of the events that you must log to conduct security auditing:

i. Look for permitted connections

This event id is generated whenever the Windows Filtering Platform allows an inbound or outbound connection. Since this is a high-volume event, we recommend auditing only if every network connection to a server or application needs to be tracked. For example, a browser connecting to the internet versus PowerShell making an outbound connection.

ii. An application or service is permitted to listen on a port for incoming connections

Windows Advanced Auditing Policy overlaps with the basic Windows auditing policies stated above. However, these are recorded and applied differently. Advanced auditing empowers administrators to be more selective in the number and types of events to audit.

For instance, if you enable success auditing for the basic Audit account logon events, success events for all account logon-related behaviors will be logged. However, with advanced auditing policy, administrators can select only the behaviors they want to monitor and exclude audit results for behaviors that are not important. Administrators can enable success events for one subcategory of account logon category, failure events for another subcategory, and choose to not audit the rest of the subcategories. Such granular control over audit policy largely reduces noise and false positives while spotting security threats.

We've mapped a few events that you need to monitor and that fall under the advanced auditing policy, with the security use case it can detect.

1. Detecting privileged account abuse

An attacker will not always end up with an account with higher levels of access. So they will try to elevate the level of access of any account they get their hands on. They also try to access privileged user accounts to take control of the entire network. Therefore, we need to monitor for unauthorized privilege access attempts.

Analyzing the following events will provide insights into privilege abuses.

i. Privileged service was called

This event id is generated when SeSystemtimePrivilege, SeCreateGlobalPrivilege, or SeTcbPrivilege is called. You can have a list of allowed and denied user rights or process names and trigger alerts for misuse of "Privileges" and "Process Name" fields.

Monitor this event with the “Subject\Security ID” or “Account Whose Credentials were Used\Security ID” that correspond to the accounts that indicate malicious actions.

You should also check if the user has logged in outside the authorized hours or used an unauthorized workstation to do it (Event ID 4776).

Correlate the file and folder changes (Event ID 4663) which are immediately followed by privileged access attempts.

2. Detect Kerberoasting and spraying attacks

In Kerberoasting attacks, the service account credential hashes are extracted from Active Directory for offline cracking. This attack is very effective when people create poor passwords.

Every Kerberos ticket is stored with AES128-CTS-HMAC-SHA1-96 encryption (from Windows Server 2008 and Vista). Attackers request Kerberos service tickets which are then exported for decryption. Different New Technology Local Area Network Manager (NTLM) hashes are used to do this, and once the ticket is successfully opened, the correct service account password is discovered.

i. Request for a Kerberos ticket

Attackers may request hundreds of service tickets hoping to find the password in any one of them. So lookout for a spike in requests for service tickets.

Use the following filters to reduce noise

• 1. Ticket Options: 0x40810000
• 2. Ticket Encryption: 0x17

ii. Failed pre-authentication

This event is generated every time the key distribution center fails to issue a Kerberos ticket-granting ticket (TGT). Look for mass records of Failure code 0x18 which could indicate possible Kerberos spraying.

3. Monitor external devices that is being used in your network

Sometimes rogue employees might try to steal information using external storage devices. The main purpose of USB device analysis is to identify the devices connected to your network and monitor the usage metrics—files copied to or from the device, connection time, etc.

i. External device recognition

This event id can be used in servers or networks where important information is stored. Set alerts for this event whenever the Subject\Security ID field is not SYSTEM.

4. Watch out for potential malware activity

Malwares use scheduled tasks to perform malicious actions after they enter the network. They are also used to maintain a presence in the network by installing backdoors or remote access tools to enter effortlessly after every reboot.

i. Monitoring newly created scheduled tasks

ii. Creation of new processes

Every malware can execute a code by creating a new process, once it's inside the network. This process will automatically launch depending on the attack type (sometimes days or months after infiltration).

By tracking this event id 4688, you can trace the instances of the malware processes, and find possible spreading to other devices in the network.

iii. Monitoring registry changes

This event id lets you capture unauthorized processes that change registry values and spot malware activity or suspicious changes to key registry values. Enable auditing and alerting on systems containing high-value data, domain controllers, and servers. Take regular backups of the registries in case anything goes wrong. Know more about tracking registry modifications.

5. Single account trying to log in to multiple hosts

Most users log in to one or two systems during a typical day. But user accounts that try to log in from different machines may indicate compromise. Remote logins can indicate possible lateral movement.

i. Successful logons

Monitor the Logon Type field for categories 2,3,9, and 10.

2 - Interactive Login: Indicates a user logged into the system by using the keyboard.

3 - Network: The user has logged in to the computer from somewhere else within the network.

9 - New credentials: The user could have used different credentials to access any sensitive areas or execute admin-level commands (Runas) on the computer.

10 - Remote Interactive: Indicates that the logon was through Terminal Services or Remote Desktop.

Sysmon (System Monitor) is a Windows system service and device driver that comes as a part of Windows Security utlities and logs events to Windows event logs. Sysmon logs provide information on process creation, network connection, and changes to file creation time.

Some Sysmon log information and regular Windows event information overlap. However, Sysmon logs possess below additional information that differentiates it in security auditing.

Sysmon logs:

• 1. Provide information on both current and parent processes.
• 2. Record the hash of process image files using SHA1, MD5, SHA256, or IMPHASH.
• 3. Include information on the process GUID, which acts as a unique parameter allowing correlation of Windows events that reuses the process IDs.
• 4. Include the session GUID, which acts as a unique parameter for session monitoring and correlating different events occurring on the same logon session.
• 5. Provide details on the loading of drivers or DLLs.
• 6. Help detect changes in file creation times to understand when a file was actually created.

As you can see, Sysmon logs provide critical details that help you to hunt down security threats effectively and proactively.

Below, we'll look at what kind of threats can be detected or prevented by monitoring specific Sysmon events.

1. Detecting malware from phishing attacks

Phishing is one of the most commonly used techniques to break into a corporate network. Phishing scams are often used to drop malicious programs in the network that can cause data breaches or launch ransomware attacks.

Attackers may send bulk emails to employees to trick them into initiating malicious processes. Once the process or task is created, the attacker can compromise accounts, exfiltrate data, or laterally move within the network to exploit other systems. Sysmon analysis helps spot and contain malware at the earliest stages.

Process Creation - Event ID 1

Just like Windows event ID 4688, Sysmon event ID 1 tracks all the newly created processes along with when they are terminated. But this Sysmon event gives you more information on the parent process ID, location of the parent process, and more. This helps with tracking the process hierarchy, which comes in handy during forensic investigations.

Attackers send malicious files or links in the emails that can download payload data onto your systems when executed. This payload can then be used to:

• 1. Find credentials.
• 2. Download additional malware.
• 3. Encrypt files in the network.

File creation events - Event ID 11

The most critical resources needed for a system to function properly are stored in the C drive. Attackers can drop malware in this drive, so that it gets loaded along with the boot files during startup.

This event detects file creation in places inside the C drive, like temporary, and download folders where malware can be configured to create files when needed.

File stream creation detection - Event ID 15

Each downloaded file from the web is tagged with a Zone.identifier tag by the browser. This tag contains information on the zone from which the file originated and the URL from which it was downloaded.

The Zone ID values indicate different sources, such as:

• 0 - Local computer
• 1 - Local intranet
• 2 - Trusted sites
• 3 - Internet
• 4 - Restricted sites

This information can be used to trigger security responses on the downloaded files.

Event ID 15 is generated whenever a file stream is created and contains the following data:

• Image - Application that was used to download the file.
• TargetFileName - Name of the downloaded file.
• HostUrl - The site from which the file was downloaded (from the Contents field).
• User - The account name of the user that initiated the event.
• Computer - The workstation where the event was logged.

2. Detecting Mimikatz activity in your network

Tools such as Mimikatz are used by malicious actors to extort credentials from the memory. These tools can extract passwords, hashes, Kerberos tickets, and more.

When installed into your system, the tool (Mimikatz), which is started as a process, accesses credential storage areas such as lsass.exe to dump the credentials. It is difficult to detect such activities with Windows log auditing because the parent process isn't known. Therefore, Sysmon analysis provides better visibility and helps connect different events to stop the attackers at their initial stages.

Detecting a process accessing another process - Event ID 10

Set the TargetImage=C:\Windows\system32\lsass.exe in the config.xml file to detect when any process tries to access lsass.exe.

Look for Sysmon logs with the event ID 10.

3. Registry modifications

Attackers may try to modify the registries to launch a malicious application or service during system startup. They can sometimes modify a whole registry or a particular key value in it to achieve this. One such example is the password filter DLL attack, where the hacker injects a malicious DLL file in the HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Control\ Lsa > Notification Packages registry.

So, you need to monitor registry changes as they can help you:

• 1. Capture unauthorized processes that change registry values.
• 2. Track privileged accounts and prevent malicious actions.
• 3. Spot malware activity or suspicious changes to key registry values.

Here are some sysmon events that you need to monitor:

Creating and deleting objects - Event ID 12

This event tracks the key and value creation or deletion operations of specific registries.

Tracking value modifications - Event ID 13

This event ID tracks registry value changes made by attackers.

Renaming keys and values - Event ID 14

This event tells you when the registry keys and values are renamed along with the new name given to it.

4. DNS traffic identification

Attackers may use the application layer protocols to avoid detection by blending in with regular traffic. Using these protocols they can send commands to the Command and Control servers to drop payloads or exfiltrate data. One of the places you need to monitor for anomalous behavior is DNS traffic.

Execution of DNS queries - Event ID 22

This event ID is generated whenever a process executes a DNS query. You can use this event ID to check the process origin and the final query executed by the process. This event ID is supported only on Windows 8.1 and later.

Detecting network connections - Event ID 3

This event ID is generated whenever there is a TCP/UDP connection on the machine. You can use both Event ID 22 and 3 to check for DNS queries.

This event ID gives you information on the image being used, port name, and destination address. For example, if you see a process accessing a server using an SSH port, it could be malicious.

FileCreateStreamHash - Event ID: 15

This event can be correlated with event ID 22 to see the name of the file they downloaded and the source URL. The hash provided from this event ID can be used to check if the same operation was done on any other system in the network.

5. Detecting lateral movement

Detecting lateral movements in your network can be a challenging task. When attackers gain admin privileges, it becomes especially difficult to differentiate malicious actions from legitimate ones. With a SIEM solution capable of Sysmon monitoring, you can quickly detect attempts to move laterally.

Creation of new processes - Event ID 1

Once the attacker gains access to a host, they can spread malware to other devices by using trusted Windows tools like PsExec. They might also change the name of the executable to evade detection. For example, they can rename their executed process to PsExec.exe, which will remain undetected if you had set alerts for the original process name.

Event ID 1 retains the original metadata (OriginalFileName) of the executable to give you the opportunity to get alerts upon attempts to evade detection by renaming processes.

Detecting network connections - Event ID 3

Attackers may try to connect to critical servers once they get access to a system in the network. A standard user trying to connect to a server to which they don't have access is a suspicious event. This event ID tracks all the TCP/UDP connections on the machine. Using the source and destination hostnames and IP addresses, you can find out which system was compromised.

6. Detecting process tampering

Attackers have been using techniques like process hollowing and herpaderping to execute malicious code masked under legitimate processes.

Process Hollowing - A technique that deallocates legitimate code in a trusted Windows process and then replaces it with a malicious code when needed. This malicious code will now run under a legitimate Windows process.

Process Herpaderping - This is a technique where the contents of the process are modified after the image is mapped. This makes the process appear harmless to the user while a malicious process runs in the memory. For example, Mimikatz can be executed under chrome.exe, making it appear to the OS that a trusted process is running with a valid Google signature.

Detecting process image changes - Event ID 25

Process hallowing has been around for years. But herpaderping is a relatively new and powerful approach used to remain undetected if auditing is not enabled.

This event detects the process hiding techniques explained above. The Image field in this event ID gives you info on the process that was tampered with.

We recommend forwarding this event to a SIEM tool that can correlate many events to give you info on who performed the attack and how far it has spread in the network.

Tuning Sysmon config.xml

Since Sysmon auditing is noisier than Windows auditing, it's a best practice to decide on the files and folders you want to include and exclude from monitoring, and keep the file length to a minimum. This reduces management issues and helps you collect only the things you really need. This event filtering is done using the config.xml file.

Example

When an intruder gains access to this configuration file, they can easily find out the places you are monitoring and exploit someplace you're not. So, you should monitor these registry keys and files for suspicious changes:

• Computer\ HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Sysmon64 (service responsible for monitoring).
• Computer\ HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ SysmonDrv (communicates the state of the events generated).
• The config.xml filename and its location.

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