All posts by misnomer

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 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
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.
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.

False Positive in a SIEM

People always try to convince me that SIEM gives a lot of false positives. I am surprised by this accusation of a “Passive” Technology like SIEM that I decided to blog about it. I call SIEM technology to be Passive in the first place because these systems are not changing anything on the IT Infrastructure nor are they Defending against anything. They are simply a “log pattern matching” tool. It’s as true as the logs being fed into it for Matching against what SIEM Industry calls as Correlation Rules. Correlation rules in SIEM are nothing but a set of patterns in the Logs to watch for and alert on.

Lets take an example of a typical SIEM Analysis scenario

Rule in SIEM – Identify Port Scan or Network Scan happening in the Network followed by successful connection on an open port.
Rule Logic – IDS Signature based detection or Pattern Based Detection from Network Firewalls (X number of Port Connections in Y Time from the same IP Address)
Rule Output – Source IP, Destination IP, Port Numbers

Based on the IP Address and Port information, analysis was done on what is happening in the Network between these two machines. At the end of the Analysis the Security Analyst found that the behavior of Source IP is expected or normal and there is nothing malicious about it. He collects the evidentiary data (whether the data collected justifies this behavior or not is a different question but not important at this point in time), follows the Incident Management life cycle and closes this Incident as “False Positive”.

For me, categorization of the Entire Event as False positive is where the problem is. This is not a False Alarm. This Alert did what it was supposed to do or rather designed to do. The Pattern Matcher detected the pattern and triggered an alert. If the pattern is wrong, the pattern needs to be updated and not deemed as False Alarm. From a Security Point of view, this entire Analysis might help in understanding your Network better, Applications better and the Security Gaps better.
In my life, I have come across several instances where such “False Positives” have turned out to be gold mines to gather valuable information about the things happening in your network. Sometimes, such events open our eyes to previously unknown or unseen Security Risks in the organization.

For me they are just “Positives” and there is nothing “False” about it!!!

What and How much to Collect – Enterprise Security Logging

One of the major challenges in Enterprise Log Management is “What to Collect and How much to Collect?”. The How to collect is the easy part with several Enterprise as well as open source tools available in the market that help with this. Source Device themselves have several log forwarding mechanisms and features which we can leverage to collect logs.
Most of the times, Log Collection and Management is driven by Standards, Compliance Requirements and other external drivers. Good Security Practice calls for Log Collection and Management to be driven by Enterprise Policy. So in order to implement a Log Management Program, the need to have a strong Enterprise Policy is paramount. This policy once defined should be implemented thoroughly right from the OS Build, Application Certification, IT Infrastructure Design to Solution Approval, Change Approval, and other Operations Process.

What to Collect:

“Never start Log Management Program without knowing your IT Infrastructure”. This is what I would suggest to anyone who wants to start Log Management Program. Knowledge of the network is important to decide on Log Collection Scope and Volume. Generally, we collect logs for several reasons ranging from Troubleshooting IT Issues to Forensic Investigation. My focus in this blog post is of course on Security Specific Log Collection. I would like to mention here that there is no right or wrong way in approaching Security Log Collection and hence what I am trying to catalogue here are my experiences of what has been useful in Security Investigations in my career.

  • Core Router– Though Router Logs are chatty, collection of Core Router Logs are important because, if your enterprise Core Router is over-run/compromised then your enterprise is wide open. These router logs can be heavily filtered to identify only DoS/DDoS attack scenarios as well as Exploit Scenarios (By exploiting a vulnerability and owning the router).
  • Network Firewall– Firewall Logs are the most helpful in identifying Security Incidents involving Malware, Compromised Hosts, Spam Relays and several other Network based Attacks and Compromises. Keep in mind that the logs don’t directly tell you that a Malware is found in the network, but it gives a great corroborating evidence (In terms of when and what connection was made) to any of your Security System Alerts.
  • Network IDS/IPS– Intrusion Detection Systems are a crucial part in the Security Incident Detection and Investigation process. The alerts received from the IDS/IPS gives a lot of information. This when combined with Firewall Logs help to identify the entire Attack Scenario.
  • Authentication Servers– In a Network there are several Authentication mechanisms for users to access IT Infrastructure. Most of them go off a Directory service or Database service. Most famous of the these Authentication servers are Active Directory/LDAP, RADIUS, TACACS, Internal User Database etc. From a Log collection perspective, in order to identify the User, his machine and the Authentication time stamp, we would need logs from Authentication Servers.
  • Endpoint Security Solutions– The last line of defense in any organization is the Security Systems put on the Servers or the End User machines. These tools can be of great help in a Security Investigation by providing information on whether the Host Defense system detected an intrusion or not.
  • Application Servers– Application servers are the main reason one has to protect the network. The application servers be it Web or Database are critical to an Enterprise. We would need to monitor these systems closely for any kind of breach of compromise by collecting logs from Operating System Level as well as Application Level
  • Misc Logs – In addition to the above critical log Sources, Enterprises may choose to collect Logs from other supporting IT Infrastructure as well. This however is an all-inclusive list of devices like Proxies, DHCP, DNS, Other Security Tools in the environment, Switches, WAN Devices etc

How much to Collect:

One of the oft ignored aspects of Log Management is Standardization of the Logging Infrastructure. This means that the format should be standardized so that all the Logs can be collected in a Centralized fashion and used for normalization, integration with SIEM Solutions, etc. Almost all the solutions support Syslog as a Logging Format. Network Devices and Unix Devices have Syslog daemons running natively and can be used to send logs to a Central Logging Infrastructure. As far as I know, most of the Security Appliances/Servers also have Syslog capability. Microsoft Windows servers don’t have the capability to send Event Logs through Syslog and hence we would need to use Third-Party tools like Snare, Syslog-NG, WinLogD, Kiwi etc.
Syslog has several levels as highlighted below in the diagram and one should carefully chose the level appropriate to the Organization.

From a Security Perspective, recommendation would be to choose either Level 5 or Level 6. Level 5 mostly covers all Security related incidents logging. Level 6 gives detailed incident logging but will be very voluminous. Level 6 enabled Syslog setting would need extensive filtering to ensure the Syslog Infrastructure is not overwhelmed in volume and subsequently Storage space.

To summarize, More and More information collection through Logs would be invaluable in Security Investigation. Many would say that Log Collection is a “Reactive Approach” to Security Management but remember “Logs Don’t Lie”
I would be writing a detailed Blog post very soon to give details on What Logs to keep and What Logs to Filter. I will try to do it by device type so that it will be easy to read.

Please visit the follow-up post – What Logs to Keep and What to Filter