An alchemists view from the bar

Network Security Alchemy

The natural habitat of a network security appliance

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…Challenging the black art of tuning.

Living things have a natural habitat, an environment where they thrive because it provides all that’s needed for their survival. The evolution, and more importantly extinction of species has shown us that once the habitat of a creature changes substantially, it must either adapt to its new surroundings or it can quickly become extinct.

The natural habitat of a network security device, such as a firewall or an intrusion prevention system is the modern enterprise network. From the outside this habitat looks to be volatile and hazardous where only the strongest technologies survive.

When an organisation is seeks to adopt a new security technology, they commonly go through a process of product selection based on a key criteria, for example.

Does the product meet business goals assigned to the project
Cost of ownership & return on investment
How well does the product integrate with the operating environment
How will it perform its function on our network rather than someone else’s

Integration questions and tests are particularly important as no two enterprise networks resemble each other, however one point that commonly gets overlooked is that the modern network rarely resembles itself a few months further along the line. How well security technologies deal with this rapid rate of change can be linked to how successful their deployment will be a few months along the line.  Will the new device adapt as the environment changes? Alternatively, will it continue in a pointless attempt to enforce extinct policies that has no relevance to the state of the organisation as it is now.

When introduced to a new network, an Intrusion Prevention System needs to be configured for the environment, this is so the device can better understand the habitat it operates in and is therefore better equipped to detect or prevent intrusions. In the world of IPS this is known as the black art of tuning. A tuning process can be broken down into a couple of logical steps.
Deploying vulnerability based network attack detection or prevention capabilities for assets that require protection.
Mapping the organisations acceptable usage policy into the devices configuration.

Both of these steps provide their own challenges, for the initial configuration of a system and also it’s adaption as the network it protects evolves. Lets take a look at each one in turn and discuss methods that can employed to improve the accuracy of detection, speed of response, and adaption to the network as it and associated business goals change.

Vulnerability based attack detection and prevention.

IPS is commonly considered the current generation of network intrusion detection systems, the new kid on the block that has the ability to prevent the exploitation of network vulnerabilities or violations of acceptable use as well as alert to the presence of an attack. Deciding on what vulnerabilities the device needs to detect or protect from exploitation has traditionally been based on user input. It is assumed that the security or network team within an organization is aware of the assets and services offered by the network, and therefore in a position to decide what vulnerabilities the IPS should mitigate. Unfortunately I commonly find this assumption to be flawed.

Many organizations I speak to incorrectly believe that they have a unique problem. Not knowing what assets and services are operating on the network, and therefore not knowing what needs to be protected for which vulnerabilities. This is clearly not a unique issue as I run into it all the time, and the impact of this problem turns out to be high. Missed attacks or false alarms.

Here at Sourcefire we designed a technology back in 2003 that provides information to make this task much easier, we call it RNA – Real-time Network Awareness. RNA provides a map of what the protected network looks like right now, based on how assets and services behave or are accessed. This real-time network map provides good answers to key questions before and after security events occur.

Before an event.
What devices are currently on the protected network?
What services do these devices offer?
What vulnerabilities may exist on these systems?
What detection or prevention capabilities do I need to employ to best protect this network?

After an event.
Was the attack relevant to the device or service?
E.g. Would the target have been vulnerable to the attack. Was it an Apache attack against an IIS Webserver.
Following the attack, did the network or asset change in any way?  2E.g. Did a new service start, or a new client application communicate to the internet for the first time.

Having this real-time map of assets on the network allows us to quickly adapt to changes in the environment. For example, take the current running IPS policy, maybe one that is designed to protect public facing assets from known attacks and overlay it onto a map of what the network is right now. Are there any gaps in the defenses? Has a new service been deployed on the network without the security team being made aware of it?
Has the version of Apache been updated on our production systems? Therefore mitigating the risk of some attacks being successful.

This real-time, constantly adapting map of the network is the key component of enabling the IPS to evolve as its habitat changes. It prevents it from becoming a dinosaur and churning out useless extinct log data.

Monitoring and Enforcing an Acceptable Use

Detecting violations of the organizations acceptable usage policy at a network level is a commonly desired function of Intrusion Prevention. Although we instinctively think of Firewalls, IPS and other network access control devices preventing communications between specific computers and protocols, these communications most likely occur at the request of a user. A laptop for example is not intrinsically a malicious device as its functions are controlled by a user, so if an acceptable usage policy is violated through an instant messaging chat session, do we blame the device or the user?

Tracking down the sources of AUP violations can traditionally be tricky in dynamic environments, and as it happens these are the most common source of AUP violations. Large DHCP ranges are commonly associated with call centres or groups of office staff who will gladly whittle their work day away by abusing network resources. In these environments it can be hard to find something static to associate with an event to allow investigation. The IP address of the source has since changed, knowledge of the original MAC address has been lost due to the network topology, a user was “hot-desking”, the only static in this habitat is the person that violated policy.  This is why it is important to associate these types of events with the user of the system at the time of the violation.

This unique combination of user and network awareness providing an up-to-date map of who is accessing what on the network is invaluable when it comes to actually enhancing the security. Network information has its most value at the time of discovery, constant discovery means providing constant value.


Written by leonward

March 14, 2008 at 6:00 pm

Posted in Security

Tagged with , ,

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