The UK's National Infrastructure Security Co-ordination Centre yesterday reported a fundamental flaw with the core Internet protocol - TCP/IP - which creates a mechanism for hackers to crash vulnerable routers and severely disrupt Internet traffic. The problem stems from the fact that it's far easier to reset TCP/IP sessions using spoofed packets than previously thought.

Routers running Border Gateway Protocol (BGP) are most severely affected by the vulnerability because the protocol relies on a persistent TCP session between BGP peers. These sessions, though easily restarted, could be disrupted as a result of the flaw. Other application protocols such as DNS (Domain Name System) and SSL (Secure Sockets Layer) are potentially vulnerable but to a lesser extent than BGP.

The vulnerability is serious but early predictions of doom are somewhat wide of the mark. Various workarounds exist and vendors like Cisco are rushing out fixes. Also, the attack does not directly compromise data integrity or confidentiality. The worst aspect of the problem is that a huge range of networking kit (firewalls, switches, and routers) from multiple vendors need attention.

The National Infrastructure Security Co-ordination Centre advisory on the vulnerability follows months of behind-the-scenes work on the issue. Security researcher Paul A. Watson is credited with mathematical analysis that first highlighted the potential problem, as explained by US-CERT here. ®

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