WEF Server, Add Missing Channels


In collaboration with Adam Swan (@acalarch), in our spare time, we have been setting up Windows Event Forwarding collections and looking at the thousands of windows logs. We then rate their corresponding volume and level of confidence related to information security (as well as for windows system admins and helpdesk). We also have been collaborating this same information with Florian Roth (@cyb3rops) who is working on essentially the same thing.

This post assumes that you have set up the basics of Windows Event Forwarding / Windows Event Framework / Windows Event Collection / Windows Event Subscriptions. (relevant side note: Microsoft apparently hasn’t identified a common lexicon when talking about windows events & subscriptions). 

The Problem
While we were attempting to collect logs from certain clients we would notice that they had software that had windows event log locations which were not on the WEF server. When you create a subscription to a computer and you go to select an event channel to pull from, the list of event channels is populated by what is available on the subscriber (the server collecting the events). Therefore, if a channel exists on a client being collected from but not on the subscriber, the channel will not be available (see figure x). Also, performing registry hack may sometimes cause instability. (ie: In HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WINEVT\Publishers;HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WINEVT\Channels;HKLM\System\CurrentControlSet\Control\WMI\Autologger).
Client on the left, Sysmon channel available. Subscriber on the right, Sysmon Channel Not Available. How do I subscribe to a channel that doesn’t exist locally??

The Solution

The solution, is to add the missing channels to the subscriber. You can do this by installing the manifest for missing windows event channel OR the much simpler way of adding the channel subscription in XML form. Also, https://blogs.technet.microsoft.com/russellt/2016/05/18/creating-custom-windows-event-forwarding-logs/ may be of help. First we’ll dig into a little bit of background knowledge for your sanity and then we’ll provide a step-by-step on how to create a provider for either type.

Background on Windows Events

There are basically two ways to create a channel… Classic and Manifest Based [https://msdn.microsoft.com/en-us/library/windows/desktop/aa364161(v=vs.85).aspx]. This post will describe how to create the channel for either.

Creating a Classic Channel:

This will only work for Logs that are NOT under the“Application and Services Logs” path.
This is an easy one liner in powershell “new-eventlog –Logname “ThelognameIwanttocreate” –Source “TheSourceIwishTocreate”

Creating a Manifest Based Channel:

This Involves Two Steps:
  1. Collect the manifest off of a computer where the channel exists already or from the executable that creates the channel
  2. Install Manifest using wevtutil im manifest.name

Background for Manifest
The manifest for a channel is an XML document that describes a provider. The provider name becomes, the name for your channel as you are used to seeing in the Windows Event log. [https://msdn.microsoft.com/en-us/library/windows/desktop/dd996930(v=vs.85).aspx]

Obtaining the Manifest You Need
There are several ways of going about getting the manifest. It may be published online. In the case of sysmon, simply running “sysmon –m” will install the event manifest and nothing else. Other times it can be quite tricky to find it. Here are some methods we’ve tested and had success with.

Windows PerfView

The easiest way is to try your luck with PerfView by Windows [https://www.microsoft.com/en-us/download/details.aspx?id=28567].
Perfview has a command “dumpRegisteredManifest”. This command will dump the Manifest for the specified channel into the current working directory. This worked for most channels, we tested.
Running “perfview /nogui /accepteula userCommand DumpRegisteredManifest [Channel-Name]” on a host to obtain the desired manifest.
Notepad++ (or any of your favorite IDE/text editor)
Another way to obtain the windows event manifest is to search for it inside the executable you believe contains the manifest. Notepad++ has a decent search utility that will allow you to search for the manifest. Try keywords that should exist in the manifest for each of the executables associate with the channel such as “eventman.xsd” (you may also want to try “e.v.e.n.t.m.a.n.\..x.s.d” as the manifest may be stored in Unicode).
Sysmon Manifest found within the executable.

Installing the Manifest

Luckily installing the manifest is a simple one liner. The resources could not be found error should be expected as we are installing the manifest without installing sysmon, the channel will still appear in the windows event viewer.
“wevtutil im mymanifest.whatever”

Final Thoughts

It’d really be nice if Microsoft would go ahead and just make the manifests exportable without installing additional tools. Additionally, if you are a developer be a scholar like Mark Russinovich (sysmon) and publish your manifest or make it easily installable.
tag:Add Client Log Channel to WEF Server

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