Security Basics: Know What's on Your Network

This post is one in a series of blog posts on the fundamentals of an information security program. You can see the complete list of posts in this series here.

The most basic of basic security principles is that you must know what you are defending in order to defend it. It sounds obvious at first blush, but it is an oft-neglected step in securing your network, your systems, and your information. Getting a handle on what devices are present on your network is essential to a proper security program.

One of the notes in the Office of Personnel Management (OPM) Inspector General's report on their systems security in November 2014 (just before they suffered a massive breach) was that the office did not "maintain a comprehensive inventory of servers, databases, and network devices."1 This shortcoming clearly underlies many of the other shortcomings there, including the failure to conduct comprehensive vulnerability scans -- you can't be sure if you're scanning everything if you're not sure what "everything" is.

Proper device inventory impacts security in a number of important ways:
  1. As noted above, not knowing what is on your network means your other security measures are all likely to be less effective. Systems not accounted for in an inventory may be unprotected by a firewall or IDS, may not have antivirus installed, may go unpatched, may have outdated accounts present, may have sensitive data that shouldn't be there, and so on. Many, MANY breaches have been known to result from unaccounted-for systems, to include healthcare.gov2, JPMorgan3, and Vermont Health Connect4.

  2. Once you know what is SUPPOSED to be on your network, you want to know what ELSE might actually be there. Monitoring of the network provides awareness so that if new hosts or devices are introduced the administrators will be know. These may be legitimate or semi-legitimate devices introduced by staff members either mistakenly or without proper planning and approval. Or they may be truly illegitimate devices introduced by malicious parties to attack the network or steal data.

  3. Ideally you want strong measures to control what can get onto your network, so that simply because someone plugs a device into a jack that device won't necessarily be able to access the various devices and services on your network (wifi presents an even larger challenge). This can be accomplished to some degree via network scanning and monitoring, along with control over wifi, network ports, and DHCP, but a Network Access Control system (NAC) provides a higher degree of security, prevention, and automation. These systems can segregate a newly-introduced system until it authenticates itself and is tested for compliance with security requirements (e.g., installed patches, anti-virus, configuration details).

1. https://www.opm.gov/our-inspector-general/reports/2014/federal-information-security-management-act-audit-fy-2014-4a-ci-00-14-016.pdf
2. http://www.nytimes.com/2014/09/05/us/hackers-breach-security-of-healthcaregov.html
3. http://dealbook.nytimes.com/2014/12/22/entry-point-of-jpmorgan-data-breach-is-identified/,
http://www.darkreading.com/perimeter/jpmorgan-hack-2fa-mia-in-breached-server/d/d-id/1318391
4. http://www.healthcareinfosecurity.com/hackers-are-targeting-health-data-a-7024

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