Monday, May 17, 2010

Logon Type Codes Revealed

The logon/logoff category of the Windows security log gives you the ability to monitor all attempts to access the local computer. In this article I’ll examine each logon type in greater detail and show you how some other fields in Logon/Logoff events can be helpful for understanding the nature of a given logon attempt.
Event IDs 528 and 540 signify a successful logon, event ID 538 a logoff and all the other events in this category identify different reasons for a logon failure. However, just knowing about a successful or failed logon attempt doesn’t fill in the whole picture. Because of all the services Windows offers, there are many different ways you can logon to a computer such as interactively at the computer’s local keyboard and screen, over the network through a drive mapping or through terminal services (aka remote desktop) or through IIS. Thankfully, logon/logoff events specify the Logon Type code which reveals the type of logon that prompted the event. 

Logon Type 2 – Interactive

This is what occurs to you first when you think of logons, that is, a logon at the console of a computer. You’ll see type 2 logons when a user attempts to log on at the local keyboard and screen whether with a domain account or a local account from the computer’s local SAM. To tell the difference between an attempt to logon with a local or domain account look for the domain or computer name preceding the user name in the event’s description. Don’t forget that logon’s through an KVM over IP component or a server’s proprietary “lights-out” remote KVM feature are still interactive logons from the standpoint of Windows and will be logged as such. 

Logon Type 3 – Network

Windows logs logon type 3 in most cases when you access a computer from elsewhere on the network. One of the most common sources of logon events with logon type 3 is connections to shared folders or printers. But other over-the-network logons are classed as logon type 3 as well such as most logons to IIS. (The exception is basic authentication which is explained in Logon Type 8 below.)

Logon Type 4 – Batch

When Windows executes a scheduled task, the Scheduled Task service first creates a new logon session for the task so that it can run under the authority of the user account specified when the task was created. When this logon attempt occurs, Windows logs it as logon type 4. Other job scheduling systems, depending on their design, may also generate logon events with logon type 4 when starting jobs. Logon type 4 events are usually just innocent scheduled tasks startups but a malicious user could try to subvert security by trying to guess the password of an account through scheduled tasks. Such attempts would generate a logon failure event where logon type is 4. But logon failures associated with scheduled tasks can also result from an administrator entering the wrong password for the account at the time of task creation or from the password of an account being changed without modifying the scheduled task to use the new password.

Logon Type 5 – Service

Similar to Scheduled Tasks, each service is configured to run as a specified user account. When a service starts, Windows first creates a logon session for the specified user account which results in a Logon/Logoff event with logon type 5. Failed logon events with logon type 5 usually indicate the password of an account has been changed without updating the service but there’s always the possibility of malicious users at work too. However this is less likely because creating a new service or editing an existing service by default requires membership in Administrators or Server Operators and such a user, if malicious, will likely already have enough authority to perpetrate his desired goal.

Logon Type 7 – Unlock

Hopefully the workstations on your network automatically start a password protected screen saver when a user leaves their computer so that unattended workstations are protected from malicious use. When a user returns to their workstation and unlocks the console, Windows treats this as a logon and logs the appropriate Logon/Logoff event but in this case the logon type will be 7 – identifying the event as a workstation unlock attempt. Failed logons with logon type 7 indicate either a user entering the wrong password or a malicious user trying to unlock the computer by guessing the password.

Logon Type 8 – NetworkCleartext

This logon type indicates a network logon like logon type 3 but where the password was sent over the network in the clear text. Windows server doesn’t allow connection to shared file or printers with clear text authentication. The only situation I’m aware of are logons from within an ASP script using the ADVAPI or when a user logs on to IIS using IIS’s basic authentication mode. In both cases the logon process in the event’s description will list advapi. Basic authentication is only dangerous if it isn’t wrapped inside an SSL session (i.e. https). As far as logons generated by an ASP, script remember that embedding passwords in source code is a bad practice for maintenance purposes as well as the risk that someone malicious will view the source code and thereby gain the password.

Logon Type 9 – NewCredentials

If you use the RunAs command to start a program under a different user account and specify the /netonly switch, Windows records a logon/logoff event with logon type 9. When you start a program with RunAs using /netonly, the program executes on your local computer as the user you are currently logged on as but for any connections to other computers on the network, Windows connects you to those computers using the account specified on the RunAs command. Without /netonly Windows runs the program on the local computer and on the network as the specified user and records the logon event with logon type 2.

Logon Type 10 – RemoteInteractive

When you access a computer through Terminal Services, Remote Desktop or Remote Assistance windows logs the logon attempt with logon type 10 which makes it easy to distinguish true console logons from a remote desktop session. Note however that prior to XP, Windows 2000 doesn’t use logon type 10 and terminal services logons are reported as logon type 2.

Logon Type 11 – CachedInteractive

Windows supports a feature called Cached Logons which facilitate mobile users. When you are not connected to the your organization’s network and attempt to logon to your laptop with a domain account there’s no domain controller available to the laptop with which to verify your identity. To solve this problem, Windows caches a hash of the credentials of the last 10 interactive domain logons. Later when no domain controller is available, Windows uses these hashes to verify your identity when you attempt to logon with a domain account.


I hope this discussion of logon types and their meanings helps you as you keep watch on your Windows network and try to piece together the different ways users are accessing your computers. Paying attention to logon type is important because different logon types can affect how you interpret logon events from a security perspective. For instance a failed network logon on a server might now be surprising since users must access servers over the network all the time. But a failed network logon attempt in a workstation security log is different. Why is anyone trying to access someone else’s workstation from over the network? As you can see, it pays to understand the security log
aken from ntsecapi.h in the security subdirectory on the Win32 SDK CD. Used by a logon process to indicate what type of logon is being requested.
Interactive = 2,   // Interactively logged on (locally or remotely)
Network = 3,       // Accessing system via network
Batch = 4,         // Started via a batch queue
Service = 5,       // Service started by service controller
Proxy = 6,         // Proxy logon
Unlock = 7         // Unlock workstation
Logon Events (interactive):

A successful logon event generates Event ID 528, Logon Type 2. A logoff event generates Event ID 538, Logon Type 2.
Connection Events (network):

A successful Net Use or File Manager connection or a successful Net View generates Event ID 528, Logon Type 3.
Connection events are sessions at the server level and are generated only by the initial connection from a particular user. Later Net Views or Net Uses from the same user to the same computer do not generate logged events unless the user has disconnected (or has been autodisconnected) from all shares.

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