The Perils of Deep Packet Inspection
Source: Thomas Porter - Posted by Joe Shakespeare   
Network Security This paper looks at the evolution of firewall technology towards Deep Packet Inspection, and then discusses some of the security issues with this evolving technology.

Microsoft, Cisco, Checkpoint, Symantec, Nortel, SonicWall, NAI, Juniper/Netscreen, and others, have, in the past eighteen months started manufacturing firewall appliances that implement Deep Packet Inspection (DPI). In general, the DPI engine scrutinizes each packet (including the data payload) as it traverses the firewall, and rejects or allows the packet based upon a ruleset that is implemented by the firewall administrator. The inspection engine implements the ruleset based upon signature-based comparisons, heuristic, statistical, or anomaly-based techniques, or some combination of these.

Deep Packet Inspection promises to enhance firewall capabilities by adding the ability to analyze and filter SOAP and other XML messages, dynamically open and close ports for VoIP application traffic, perform in-line AV and spam screening, dynamically proxy IM traffic, eliminate the bevy of attacks against NetBIOS-based services, traffic-shape or do away with the many flavors of P2P traffic (recently shown to account for ~35% of internet traffic), and perform SSL session inspection.

Deep Packet Inspection essentially collapses Intrusion Detection (IDS) functionality into the firewall appliance so that both a firewall and an in-line IDS are implemented on the same device. Many of these products have recently been shown to be vulnerable to exploitation of software defects in their DPI inspection engines, however. These data suggest that the addition of these enhanced functions to firewalls may, in fact, weaken, rather that strengthen network perimeter security.

Read this full article at Thomas Porter

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