Identifying Suspicious Activity on your Edge Device – Part 1


Most of the good firewalls out there have the capability to identify suspicious activity and lof this information for you. However, there are some scenarios where you want more than just knowing what happened, you want to build a better footprint of the potential attack that the edge device is passing through. This post will explain how to combine the power of Event Viewer with the flexibility of Network Monitor Wizard to build trigger an action when an incident happen. To achieve that we will divide the post in two parts, this part one will explain the scenario, identify the issue and work on the data gathering process. For this post we will use Forefront TMG 2010 as our edge device; however the same approach can be used in any device that logs its major alerts to Windows Event Log.


The true value of having logging enabled on your system is the capability to review it and identify suspicious activities that took place during that time. In this particular case the Firewall Administrator identified the following entry in the Event Viewer:


When reviewing such event, pay attention to the following fields:

  • Logged: this field provide the time and day that such event took place. Notice here that it took place 3:31AM, which in this particular case is a non production hour (first flag).
  • Event ID: this field is important because you will use it to filter all events with the same ID. The goal is identify if there are more than one event like that on your system.
  • General: the text on this field means a lot; read it carefully and observe the IP address that it is available there. Once you filter the events by the Event ID, you should check if the IP appears is the same on all events. In this case it did (second flag).

The reason why I added the flags is because usually when you raise two flags while analyzing potential suspicious activity you have enough reason to move forward in the investigation process. Is important to also mention that in this particular scenario, as I’m using Forefront TMG as example of Edge device, the same event that you see on Event Viewer will be also available at Monitoring/Alerts within TMG’s console as shown below:



Now that you identified the suspicious activity on your edge device and you know which IP address you should hunting for, you can move forward. The information gathering will vary according to your internal process to respond to incidents; however there are usually some commons steps that can be used during this process, such as:

  • WhoIs: type (where W.X.Y.Z is the IP address that you are trying to lookup).
  • Bing: Bing has the capability to look for all domains that are using a particular IP. To know more about this feature, download the presentation “Lord of the Bing” from Black Hat 2010.
  • DNS Query: once you have the domains and the IP that belongs to this host, you can use nslookup to know more information about the records that are part of this domain.

All those methods are passive and the goal is only to know more about who is originating that suspicious traffic against your edge device.

Moving Forward

The second part of this article will explain how to capture live data and how to connect the dots to formulate your final conclusion.

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