April 5, 2012 2 Comments
Once again I received inspiration for this post from the Mandiant M-Trends 2012: An Evolving Threat report and reflecting on a previous work engagement where the attackers leveraged lateral movement to move around and deeper into the network. On page 12 the report highlights the attackers leveraging at.exe (task scheduler) to install malware and take control of systems. This post hopefully will help you get an idea of what your current scheduled tasks look like and get you thinking about ways to find badness when it occurs. Yes it will occur!
In the M-Trends example the attacker creates a a NetBios session first and then runs the at.exe command which to schedule the malware they previously uploaded over the NetBios session. This two steps should create some events in the Windows event logs, assuming auditing is turned on. For the NetBios connection an event id of 540 for XP and Server 2003 systems should be created and an event id of 4624 for Vista and Server 2008 systems. For the at.exe an event id of 602 for XP and Server 2003 systems and an event id of 4702 for Vista and Server 2008 systems.
To get to the point where you can actually hunt for at.exe events you must do a little leg work.
Set the audit policy:
At a minimum you need to have a few things turned on in the Local Security Policy for the Auditing Policy. You will want to enable Success and Failures audits for the following audit policies.
- Audit account logon events
- Audit logon events
- Audit Object Access
It should be noted if possible you should turn on as many of the available audit policies as you can for your environment where you can. Having these logs helps find not only badness but misconfiguration and other issues that might creep up. They are easy to setup and push out via Group Policy Objects (GPO) but just make sure you watch changes to the GPO in your logs. Some attackers have been known to modify GPO’s and turn settings off.
Now that you have your Auditing Policy in place you need to enable logging.
For central windows logging that should work with almost any commercial or open source central log collection tool I recommend using Snare as your agent for getting the logs from your windows systems to what ever central log system you have. You do have one right?
The install for Snare is pretty straight forward and is covered pretty well in their documentation, and so is adding a remote Syslog host so I won’t cover that here. What I will cover is one minor addition that I have found that needs to be made to capture and send at.exe related event logs. Start by logging in to the Snare Configuration page and select Objectives Configuration on the left hand side. When editing the auditing configuration here is what I have used in my testing to get the logs I am interested in for this hunting trip:
After adding the configuration above go to the left navigation bar and select Apply the Latest Audit Configuration. Now you may want to test and try and create a at.exe event on the system you just applied this configuration to. To test it you will need to either be a domain admin or a local admin of the system. A sample test you could use from the command prompt is:
at.exe \\srv1 07:30 cmd /c ping.exe 18.104.22.168
Change srv1 with your host name and change what is after the cmd /c to something you want the system to execute. The command above will create a task to run at 7:30 in the morning and will execute a ping to 22.214.171.124
Now go back to your Snare Configuration and look at the Latest Events and you should see near the top the scheduled task you just created.
Hunting with Logger
Now that you have configured the audit policy and you have configured Snare. Its time to go hunting for the logs. In this hunt we are using the free version of ArcSight Logger (in future posts I will explore using Snare, ELSA and maybe a few other tools). I am going to assume your logger instance is already setup and you have a smart connector in place to receive logs from Snare.
Quick Initial Search
A quick and dirty search for looking for scheudled tasks is as simple as the filter below and hitting Go!:
Now if you have any hits you might get output similar to this:
Now that you have results you should probably go make and do a search for network logon events (event id 540 or 4624) around those times to see where the commands originated from. This will help you find lateral movement.
What to do after your initial search?
We have found our initial search and hopefully all of your events are ones that were planned and not ones done by someone on your network. Perhaps you don’t want to run this query every day or so or maybe you don’t want to login every day to run it. You could quickly turn this into a report and have it run for a set interval and email you the results. I will quickly cover how to create the query and report that is needed on logger below.
Creating the Query:
Let’s create a quick and dirty query and report that can be touched up later if needed 🙂
Under the Reports Function tab on the left had side of Logger. Go to Design and select Queries then click Add New at the top. Give it a name and you could start by using a query similar to this:
select events.arc_endTime AS ‘Time’,events.arc_name AS ‘Name’,events.arc_destinationUserName As ‘Dest. User Name’, events.arc_destinationHostName AS ‘Dest. Host Name’, events.arc_message AS ‘Message’ from events where ( events.arc_externalId = 602 OR events.arc_externalId = 4702) group by events.arc_endTime
Below is what my quick Query Object looks like:
After creating the query you will need to create the report simply give it a name, select the query you just created and then select the fields you want displayed. Save the report and run it. Here is what my quick and dirty report design looks like.
Depending on your Report Start and End Times you might get data similar to your quick logger search above.
You should now have a way to hopefully find badness if there was any (assuming you have historical logs) or this can help put you on a way to monitor and find badness and respond faster.
If you have other suggestions or maybe tricks you use for these types of searches I would love to see them. We are all one big community lets help each other out where we can.
As always Happy Hunting!