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8/20/2010
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Tech Insight: Using Network Segmentation And Access Control To Isolate Attacks

The right network design can protect against hidden threats from embedded systems and rogue access points

Insider attacks might have doubled during the past year, according to new case data from the U.S. Secret Service included in the recent Verizon Data Breach Investigations Report, but external attacks are still the major threat and account for the most records stolen -- indicating companies still are not securing their networks and data properly.

Proactive security controls and secure network design can play an important part in preventing attacks both from the inside and outside. Unfortunately, without proper network segmentation and access control, once the attacker gains access to the victim's internal network, it's often game over: Sensitive servers are sitting there, just waiting to be pillaged.

A security breach does not have to end badly, however. Jennifer Jabbusch, CISO of Carolina Advanced Digital, tweeted recently, "NAC [network access control] is a philosophy, not a technology." A defense-in-depth approach to network design with segmentation and access control can go a long way to slowing down the spread of malware and preventing exposure of sensitive systems.

Vulnerabilities exposed in embedded operating systems, like VxWorks and QNX, during the past few weeks highlight the need to secure these devices and isolate them as much as possible without impacting productivity. Typical deployments of multifunction devices and similar systems, however, indicate a general lack of understanding of the security impact these systems can have if abused.

For example, new modules were released for the Metasploit Framework that allow memory to be dumped from vulnerable VxWorks devices. Within the memory dumps, passwords and internal IP addresses can be found that could allow an attacker to then log in to a network switch and change the VLAN for a device, or log into a server via an exposed service account.

Because printers and streaming media appliances are more than just dumb devices but full clients and servers, it's important to create a network segment that isolates them and provides only enough access for the needs of the business.

For example, multifunction copiers used to e-mail scanned documents should be allowed to communicate to port 25/tcp on the mail server and not telnet on a switch or Windows server ports on the file server. Likewise, embedded systems should not be allowed to access, nor be accessible from, the Internet unless that's the purpose of the device like a VBrick media streaming device.

Embedded devices are the only thing employees put on the network without thinking about how it might impact security. In vulnerability assessments of its customers, AirTight Networks found that one-quarter of the networks had employee-installed rogue wireless networks in them.

Whether for productivity and ease-of-use purposes -- or because the user was malicious -- the effect is the same: exposure of the internal corporate network to anyone within range of the wireless access point. Policy statements saying that any changes to the network, like adding a wireless access point, is strictly forbidden are good, but technical controls need to be in place to enforce them and detect any violations.

Basic technical controls, like limiting one MAC address per network switch port, is a start, but can be easily overcome by a tech-savvy employee. More advanced controls can include NAC solutions that are able to identify a wireless device and prevent access to the internal network by shutting down the network port that it is connected to, or moving the port to a quarantined VLAN.

Keeping with the defense-in-depth mantra, wireless intrusion detection systems (WIDS) can be added to provide an extra layer of protection against rogue wireless devices. They can detect new wireless networks as they become available within range of the corporate offices, and send alerts to security staff.

The PCI Security Council realized early on about the impact of rogue wireless networks, and mandated quarterly wireless scans in the PCI DSS. But quarterly scans may not be enough -- a rogue wireless device could go undetected for nearly three months between scans.

Wireless manufacturers are addressing these concerns by including WIDS capabilities in their enterprise management systems. One example is the Cisco Wireless Service Module (WiSM) that can identify, locate, and contain rogue wireless devices on enterprise networks as soon as they are detected.

The ultimate goal of any network security program should be to prevent security breaches that expose sensitive data while allowing business needs to be met. And it's definitely possible to meet that goal with proper network segmentation, policy, and technical controls.

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