Understanding Windows Logon Type 3: Network Logon

When analyzing Windows event logs, understanding logon types is crucial for identifying authentication activities and potential security risks. Among these logon types, Logon Type 3, commonly referred to as a "Network Logon," is one of the most significant and frequently encountered in enterprise environments. This article provides an in-depth look at Windows Logon Type 3, its characteristics, uses, and how to interpret related event logs.

What is Logon Type 3?

Logon Type 3 indicates a network logon, which occurs when a user or a device connects to a computer over the network without physically logging onto the console or using a remote desktop session. This type of logon is typically associated with resource access, such as file shares, printers, or accessing a service running on a machine.

Key points about Logon Type 3:

• It involves credential validation over the network.
• No graphical interface is provided, as this is not an interactive logon.
• It is commonly seen in environments where users or applications authenticate to access shared resources.

Common Scenarios for Logon Type 3

1. Accessing File Shares: When a user maps a network drive or accesses shared folders on a server, Logon Type 3 is triggered.
2. Printer Sharing: If a user connects to a shared printer over the network, their authentication is recorded as Logon Type 3.
3. Service Authentication: Applications and services running on behalf of a user or a system often perform network logons to authenticate with other systems.
4. Scripted or Programmatic Access: Scripts, automation tools, or programs that connect to network resources also use Logon Type 3 for authentication.

Related Event IDs

To monitor and investigate Logon Type 3 activities, you can look at the following event IDs generated in the Windows Security log:

1. Event ID 4624 - "An account was successfully logged on":
   • This event is generated when a user successfully authenticates using Logon Type 3.
   • Key fields to review:
     • Logon Type: Should be "3."
     • Subject and Logon Information: Indicates the account and device used.
2. Event ID 4634 - "An account was logged off":
   • Indicates that a network logon session has ended.
3. Event ID 4776 - "The domain controller attempted to validate the credentials for an account":
   • May appear in domain environments, providing details about credential validation attempts.
4. Event ID 529 (Windows Server 2003 and earlier):
   • Indicates a failed network logon attempt (predecessor to Event ID 4625 in newer systems).

Log Analysis: Identifying Normal and Suspicious Activity

While Logon Type 3 is common in daily operations, it can also indicate malicious activity when used inappropriately. Here are tips for identifying suspicious activity:

1. Unusual Source IP Addresses:
   • Review the "Source Network Address" field in Event ID 4624.
   • Unexpected or foreign IP addresses could indicate unauthorized access attempts.
2. Frequent Failed Attempts:
   • Multiple Event ID 4625 (failed logons) with Logon Type 3 may indicate brute force or credential stuffing attacks.
3. Access Outside Business Hours:
   • Investigate logons from accounts outside regular working hours or normal usage patterns.
4. High Volume of Logons:
   • Excessive network logons in a short period may signal automated tools or malware attempting lateral movement.
5. Privilege Escalation Indicators:
   • If network logons are followed by privilege escalation events (e.g., Event ID 4670), it may suggest an attack in progress.

Securing Against Logon Type 3 Threats

1. Enable Audit Policies:
   • Ensure auditing for logon events is enabled to track and analyze authentication activity.
2. Use Network Segmentation:
   • Limit access to critical resources through firewalls, VLANs, and access control lists (ACLs).
3. Enforce Strong Authentication:
   • Implement multi-factor authentication (MFA) to mitigate the risk of compromised credentials.
4. Monitor with SIEM Tools:
   • Use Security Information and Event Management (SIEM) solutions to analyze logs in real time and detect anomalies.
5. Regularly Update and Patch Systems:
   • Prevent exploitation of vulnerabilities that attackers might leverage for unauthorized network logons.
6. Implement Least Privilege:
   • Restrict user and service account permissions to only what is necessary.

Related Article

1. Windows Logon Types and Logon Codes
2. Microsoft's Windows Audit logon events