Tag Archives: Security Investigation

Episode 3 – Security Investigation Series – Should I press the panic button?


 

Scenario:

  • A User has a machine installed with an Application Client and connects to the Web Application Server which in turn connects to the Database servers on the back-end.
  • The Client machine has been reported to be being slow.
  • Some basic SIEM based analysis of Network logs for the client machine shows some Network connections resembling a Port Scan from the client machine in its own subnet
  • The machine is also doing some random internet connections to Public IP Addresses.
  • On checking the Anti-Virus software on the machine it shows as being outdated.
  • Suspicion is that the machine is infected with some kind of a malware.
  • Since this client machine has connections to the Critical App and Database server, this event is critical

Should I press the panic button?

Before we press the panic button (raise an Official Security Incident which has SLA tagged to it), there are several questions we need answers for. This is something I learnt from one of my mentors (he blogs here). What I learnt was that before beginning a Security Incident investigation and press the panic button, we need to sit down and collect as much as corroborating data as possible. In order to do that we can follow a series of logical steps:

  1. Collect the Public IP Addresses it connects to and find out more about them. Sometimes a simple Google search can help to determine the authenticity and reputation of the website/domain or public IP.
  2. Establish Ground Zero for the infection. This can be determined by historical log data. Some SIEM tools do this natively for you. Else, you can use a white board or pencil/paper to draw this visualization yourself.
  3. Gather as much as possible infected machine IPs and sort them geographically, Network Zone based and if possible VLAN based as well.
  4. Other Transitive Infections that could be identified.
  5. Analyze one of the infected machines to gather Malware analysis data

Next Steps – Remediation, Control etc

  • Quarantine all the machines infected.
  • In case of the server, ensure that all instances (if any) of the infected file are cleaned.
  • In case of a database, if we exactly know the infection source and possible file names, try purging them from the database contents.
  • Submit the samples of the Malware to the Security Vendor and ask them to start working on a Signature or definition.
  • Perform a Reverse Engineering of the Malware to identify specific Network connections/Behaviors so that they can go into our prevention systems in the Network. (Read Network IPS, Host IPS, Proxy etc). Reverse Engineering skill set  is a good skill to have because for Zero day scenarios, vendors are slow to react. If a Reverse Engineer is available, the job of getting a control measure put in place (although a crude one) will be quicker.
  • Document the characteristics of the malware, the response taken and the findings during the course of this entire incident.
And Finally, if you did all of the above after following the Security Investigation Series blog, say thanks!!!

What is TOR? How can I Un-TOR?


TOR or The Onion Router is one of the widely used Anonymity Networks in the “Wide World Web”. Before we understand what TOR Networks are, its important to understand the basic technology involved. This is key to defining a Detection/Prevention/Control strategy in Enterprise Networks. The basic technology behind TOR is Onion Routing.
Onion routing is a technique for anonymous communications over a Network. Data Packets are repeatedly encrypted and then sent through several onion routers. Like someone unpeeling an Onion, each onion router removes a layer of encryption to uncover routing instructions, and sends the message to the next router where this is repeated. Using this approach means each node in the chain is ideally aware of only 2 other nodes:

  1. The preceding node from which the onion was transmitted.
  2. The proceeding node to which the onion should next be transmitted.

Now how is it achieved? Just like in a Routed Network, there is a master node in Onion Network that maintains the list of TOR Nodes and their Public Keys (Remember TOR uses Asymmetric Crypto). Whenever a request is made, this master node crafts the data packet in layers. Outermost Layer of encryption will be opened by the First Onion Router and the Innermost encryption will be opened by the Last Onion Router. The peeling away of each layer of the onion makes it difficult or impossible to track the onion and hence the name Onion Routing.

Some things to understand about TOR in addition to the basic technology is how it works and how hard it makes life for Security Professionals to identify and control it.

  • Firstly, TOR Nodes have to be public. Their IPs cannot be hidden. Here is a sample list of TOR IP Addresses. This could potentially serve as a blacklisting source in Enterprise Firewalls/IPS/IDS/Proxy.
  • TOR Nodes can use Bridges to connect to TOR Public IPs. Bridges are nothing but Relay IP addresses that help a client connect to the TOR Network. Bridge/Relay IP Addresses make it difficult to identify TOR entry and Exit nodes. Any user can install “Vidalia” and set up a Bridge relay to help several TOR users (who have TOR Public nodes blocked by ISP or Enterprise). These bridge IP addresses are generated randomly per Request Received. There are several such Relays and they are hidden from Public IP Pool.
  • TOR traffic is encrypted and hence detection using IDS/IPS will be difficult
  • TOR Clients have the capability to use SOCKS to set up connections and hence differentiating SOCKS doing TOR and SOCKS not doing TOR is a great challenge.
  • Several Torrent softwares have the capability to do native TOR communication. Identifying such Software Machines will be a challenge in an Enterprise having a distributed setup, Remote Access Setup etc.

Now that we know what TOR is, Don’t we need to know how to control this in the Network?
Analysis and Control of TOR can be done as follows:

1. Blacklist all known IP addresses – This essentially is not fool-proof for the mentioned reasons above with Bridging.
2. Custom Script to pool Bridge IPs and keep adding the same to IP Blacklist. This can regularly query the Bridge Mail ID to get the random list of Bridge IP addresses.
3. If your enterprise is using HTTP Proxies only, then SOCKS Protocol should not be available in your network. Identifying a user doing SOCKS can help identify possible TOR clients.
4. P2P traffic should be blocked in the enterprise as P2P and TOR go hand in hand. The key things to look for is, Browser Plugins for P2P that mask behind HTTP and HTTPS Requests. This is quite an interesting development as far as Identifying P2P Users in your network is concerned.
5. If Traffic Analysis, Flow Analysis is available in your network, you can profile your Network segments for all the Application protocols in use in your network. Unless and until you are using TLS/IPSEC through out your network, chances are that very less amount of encrypted traffic is found. Filtering through the Chaff on known Encrypted traffic should narrow you down to a list of machines that do encrypted traffic and are not supposed to or not normal.

I welcome the readers to share your experience on working with TOR and let me know of any other method of identifying and analysis TOR in Enterprise networks.

Episode 2 – Security Investigation Series – Reverse Protocol Attack


Preface: The image in the blog is a capture from the Cisco Firewall Syslog Message guide explaining an Event regarding a Reverse Protocol Attack. Cisco tells you that the packet is dropped and that the firewall defended you from a Spoofing attack. Such events are dicey in nature because you don’t know what to do, how to react and how to respond to these events in Security Operations.As with every Investigation, everything begins with a “Tip”The Tip:

  • The Event itself – In this case Cisco PIX/ASA Firewall message
  • The IP source from which the packet originated
  • The timestamp at which the event occurred
  • The Firewall from which the alert originated

Investigation Methodology:

We need to identify “who” is the person performing this attack. Since this is a firewall, all we can get is a IP address from where this originated. But from an investigation perspective, we need to identify the “real machine”doing this. If it is an internal segment or VLAN in the enterprise network we can do a few things like below:

  • Tracing the MAC address from which the IP originated. For this we would typically need Switch Logs and/or DHCP logs.
  • Identify the IP and MAC pairings logs during the said time period. Watch out for MAC address Spoofing scenarios as well.
  • Based on these two data sources we will be able to identify the physical machines which are possible candidates for this attack
  • In MAC Spoofing scenarios, looking at the physical machine will help. There is a Microsoft API that helps you gather this real MAC information. I have seen some tools that provide this information as well.
In case of Internet facing Firewall, this spoofing detection is going to be a tough ask. We may not have a capability to identify the source performing the spoof. So if the Internet Firewall throws this alert, its safe to ignore as Cisco recommends, whereas if the Internal Firewall throws this alert, it needs to be investigated to identify insider attack scenarios involving spoofing.
Detection:
Detection of this event is the simplest in SIEM terms. The event ID is unique for Cisco devices and hence they can be triggered directly. These alerts can be filtered for internal firewalls only unless and until the Internet firewall is overwhelmed with these alerts. In case of enormous amount of alerts from Internet firewall, we may have to look at potential DoS scenarios. Several threshold based rules can be created in SIEM to look for such attack patterns
Prevention:
In case of Internet facing Firewall, uRPF filtering definitely helps. There are several different modes for enabling uRPF. Before enabling we need to understand whether our network is routed symmetrically or not. In case of symmetric routing, the uRPF filtering is straight forward and we can go for Strict Mode, but in case of asymmetric routing, the filtering is not easy and hence we may configure uRPF in Loose Mode or Feasible Mode. There are several articles from Cisco on uRPF that can serve as good references.
Conclusion:
In essence, every event means different things in different scenarios. Placement of the device in the network and its relevance gives a new meaning to the event triggered. Investigation of every “event type” is mandatory in Security Operations. Results of such analysis should be fed back into a Knowledge Base that will help the enterprise react to several different alerts in the right way.
Update based on the comments received:
For scenarios where both IP and MAC spoofing is involved, there is no easy way of identifying the real machine. The closest in case of Internal Network would be to look at the Switch Network to identify the source segment of the MAC thereby narrowing done on the investigation. But even after narrowing down, you will have to go down to the Asset Enumeration level to exactly identify the spoofing host. This enumeration should be done in tandem with packet captures in the switched network. One of the other things to look at in packet captures would be to look for the presence of a Locally administered address bit. This will be set in case of a spoof. Smart hackers know this and can circumvent it by a custom driver code, but this is just another pointer of what we can look for.