EventSentry Blog

One of the upcoming features in the 2.90 release of EventSentry is file object tracking, which will – as the name implies – track file access!

EventSentry already tracks process activity by intercepting and analyzing the 592 and 593 security events that are generated when a process starts or exits respectively; we also track logons and logoffs by intercepting and analyzing the various logon (e.g. 528) and logoff events. Tracking object access turns out to be a bit more involved as process and logon tracking, since Windows 2003 and earlier don’t actually log when an object is modified, but instead log when an object handle is being returned to the caller. I would like to mention here that object auditing has been drastically improved in Vista and later, but more on that next week.

But before I explain the 560, 562 and the problematic 567 events, let’s make sure we have everything setup for auditing to work.

1. Make sure that “Audit Object Access” is active on the machine where the files will be accessed. In most cases this will be your file server, and you will probably want to configure this with a group policy object and apply this setting to all machines from which you plan on collecting object audit events.

2. Once auditing is enabled on the machine, you will have to tell Windows which files you effectively want to audit, since generating an audit event for every single file by default would fill up your security event log quicker than you could get a cup of coffee. To audit a folder, bring up the security properties of the folder, click advanced and select the “Auditing” tab. Here you will specify which accesses and users will be audited, and I recommend that you always use Everyone when adding an audit entry to ensure that all object access is audited. I also recommend only auditing the access type you really care about. since 560 events can quickly fill up your event log (and consequently any consolidated database you might have) and there is no reason to monitor accesses you’re not concerned with (e.g. ReadAttributes).

Now to get back to the 560 and 562 events, this is better explained with an example. In Windows, when you need to read or write to a file, you usually call the CreateFile() API function which will return a handle to the object (=file in this case) you are about to access. When calling CreateFile(), you tell Windows which access to the file you need. For example, when you simply need to read from a file then you can pass GENERIC_READ (or the more specific FILE_READ_DATA) for the dwDesiredAccess parameter.

Assuming that you are allowed READ access to the file, Windows will return a handle to the requested file (that you can now use in subsequent ReadFile() operations). And this is exactly where Windows logs the 560 Audit Success event (assuming of course the access type and user match the auditing enries), essentially documenting that an object handle was returned. While this all sounds nice and dandy, the problem with the 560 event is that it doesn’t actually tell you what the caller ended up doing with that handle. Even if the caller where to close the handle right away with CloseHandle(), the 560 event would have still been logged – even if the caller never actually accessed the file.

The same holds true for potential write access to a file. If I access a file with the GENERIC_WRITE access right, then Windows will log a 560 event that looks similar to this:

Object Open:
Object Server: Security
Object Type: File
Object Name: E:\Folder\Customers\Sheet.xls
Handle ID: 20084
Operation ID: {0,93244500}
Process ID: 4
Image File Name:
Primary User Name: DC1$
Primary Domain: ESDOMAIN
Primary Logon ID: (0x0,0x3E7)
Client User Name: support.engineer
Client Domain: ESDOMAIN
Client Logon ID: (0x0,0x58C5419)
Accesses: READ_CONTROL
ReadData (or ListDirectory)
WriteData (or AddFile)
AppendData (or AddSubdirectory or CreatePipeInstance)
ReadEA
WriteEA
ReadAttributes
WriteAttributes

At first glance, one would assume that support.engineer wrote to the file, after all WriteData is included in the listed Accesses. This is far from accurate however, since the user could have closed the file right-away again (without ever reading or writing data from/to it) and the event would have still been logged in exactly the same manner.

This means that unless you manually verify some properties of the file, for example the access stamps, size or checksum, the 560 events only tell you what a user could have done, not what they actually did.

When the calling process is done working with the file, it will call CloseHandle() to close the handle it had previously opened. As such, a 560 event is always followed by a 562 event that includes the same handle ID as the original 560 event.

At some point during the Windows XP development, Microsoft seems to have realized that the 560 events are limited in their usefulness (at least for authorized access), and introduced the 567 event, also called an “operational event”. The purpose of the 567 event is not to log when a handle is returned, but instead when a file is actually being accessed – much more useful – at least in theory. So even though the 567 event was created to solve the problems of the 560 event, it does so only under limited circumstances.

But since I already wrote more on this subject than most people probably want to read, I will explain the 567 event in all detail in my next post this weekend.