Using Corelight and Zeek to Support Remote Workers

by Richard Bejtlich on March 25, 2020

By Richard Bejtlich, Principal Security Strategist, Corelight

Due to the tragic Covid-19 pandemic, as we are all experiencing first hand, most governments and health officials are either mandating or encouraging those who can work from home to do so, as part of widespread “social distancing” measures. Remote workers are likely leveraging three sorts of computing models:

Using the network to access Internet resources not associated with their organization;
Using the network to access Internet resources managed by their organization but hosted by a third party, such as a cloud provider; and
Using the network to access resources hosted by their organization.

If the organization can technically, legally, and ethically instrument the remote worker’s device, such as a laptop or phone, then the security or information technology staff will have some visibility into the use of the device for all three cases. That visibility will depend on the nature of the logging available and the applications used by the remote worker.

If the organization lacks instrumentation of the remote worker’s device, they will not have visibility into the first case, as those Internet resources are not associated with their organization. For the second case, organization-managed cloud resources, the visibility will depend upon the logging offered by the cloud provider. For the third case, organization-hosted resources, the visibility will depend on the nature of the application, server, infrastructure, and network monitoring deployed by the organization.

There is one exception to the previous guidance. If the organization implements network security monitoring at the remote worker’s location, then they will have some level of visibility into all three cases. However, that is generally not a viable, scalable solution, for a variety of reasons. While it is a good idea to deploy NSM at high-value “target” remote sites, such as senior organizational leadership homes, this is not an approach that would be manageable once the site count enters the high-double or triple digit range.

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Accordingly, NSM is most likely to be of value in case three, when remote workers access organization-hosted resources. To accomplish this goal, IT staff may deploy additional infrastructure, such as virtual private network (VPN) concentrators, or other hardware and software to meet increased demand. These systems require observation as well.

IT and security should have already implemented NSM behind the VPN terminators, i.e., after external traffic has reached the VPN device and extra encryption has been removed. If there is no monitoring at this location, then that should be the first priority!

However, assuming that security teams already see traffic inside the VPN concentrators, what is the next priority?

If an intruder were able to compromise a VPN concentrator, network switch, or router, he or she would gain the advantage over defenders. They could observe, alter, or deny traffic and data when operating with such elevated privilege and access. Therefore, it is imperative that security teams recognize the need to instrument their remote access infrastructure with visibility solutions like Corelight and the Zeek NSM in order to maintain the high ground compared to their adversaries.

While the traffic to and from such devices should be encrypted, it is not the data being protected that is the concern. The worry is that intruders will attack the devices themselves. Security teams would benefit from reviewing their NSM data to ensure that only authorized parties are interacting with their remote work infrastructure. They should also ensure that the VPN concentrators and other network devices are behaving as expected, and not receiving or initiating unauthorized interactive control sessions with foreign parties.

We at Corelight wish you and your loved ones all the best in these difficult times.