The Windows event logs are stored in files with extension of
typically stored within
Unlike traditional unix style log files that consist of unstructured text, Windows EVTX files are stored in a binary format with several advantages:
While the EVTX file is actually XML based, Velociraptor converts it internally into a JSON object to make it easier to filter specific fields using VQL constructs.
Velociraptor implements a parser for EVTX files in the
plugin. The plugin takes an accessor and a filename to open the EVTX
file, and produces a single row per event.
Each event row contains three main columns:
Systemcolumn is a JSON object representing the event metadata that is common to all events, such as timestamp.
UserDatacolumns are free form JSON objects representing application specific information specific to the event type recorded.
Some of the more interesting event fields include
The Windows Event Logs architecture does NOT store the event message in the evtx file! Instead, the event log refers to an externally provided message, and the viewer application looks up the message in a database in order to display it.
This scheme has a number of advantages:
The below example shows a familiar event on a Chinese language system.
The event viewer is able to show a friendly message in the local
language, however closer inspection of the event data itself indicates
the message is not found within the
How does the Windows event viewer resolve the messages when displaying an event?
computer name, the event viewer
looks up the registry key
and reads the value
The value will point at a path to a DLL. The event viewer will then
open the DLL and search the resource section of this dll for a
Message Table resource.
Message Table is simply a table of strings. The event viewer
will then use the Event ID as an index to this message table to
retrieve the message string for the event.
The message string is a formatted string with placeholders such as
%2 etc. The event viewer will then Interpolate the UserData
section into the full string.
While the EVTX file format does have some advantages is falls short in practice on a number of levels. It is important investigator are aware of the pitfalls
Grabbing all the EVTX files off the system may result in loss of event messages!
The event description message contains vital context about what the event actually means. Without the message it would be difficult to know what each event message represents.
If we upload the EVTX files themselves from the system, and attempt to view them offline chances are that the event message would be missing on our analysis system. If we are lucky, we would be able to find some information about the message using an internet search for the event id.
If you just collect the EVTX files from one system to another you will lose access to message tables, because the messages are in DLL files scattered across the entire system.
Additionally, if an application is uninstalled, its message DLLs will be removed and earlier events are not able to be displayed any more.
In order to improve the state of event log messages, we started maintaining a set of Event Message databases in the https://github.com/Velocidex/evtx-data repository. This repository contains sqlite databases of many known message tables collected from different systems.
You can instruct Velociraptor to use one of those databases using the
message_db parameter to
Event logs can be easily disabled by simply right clicking in event
viewer and selecting
Disable Logs. The below example shows how I am
To read the full analysis of how to detect such a registry modification, read the blog post, or simply check for modifications using the
ETW is the underlying system by which event logs are generated and collected. The following diagram illustrates an overview of ETW.
ETW is essentially a broker between
Provider is registered with the system using a GUID and advertises
itself as being able to provide ETW events. A Consumer is a routine
that registers interest in a provider (e.g. Velociraptor is a
You can enumerate all providers on a system using the
logman query providers command which lists all the ETW providers' GUIDs.
In VQL watch_etw() can be used to watch for ETW events. For example,
consider the event provider
Microsoft-Windows-DNS-Client with the
ETW and event logs are just two sides of the same coin. If it possible to listen to events on the ETW layer before they are forwarded to the event log service. In this case the events are not susceptible to being stopped by disabling the log (as shown previously)
We can query the DNS client ETW provider for all DNS lookup events.
Client event monitoring queries automatically forward events to the server.