In Chapters 6 and 7, we discussed the elements and methodologies used to discover and take control of various Cisco devices by leveraging vulnerable services and common misconfigurations. We identified and explored several fuzzing tools that allow an attacker or a security researcher to find potential venues for exploitation of services in specific Cisco devices. In Chapter 8, we identified ways of finding and exploiting new flaws with examples of debugging Cisco IOS memory and processes, dissecting a known exploit by FX, and writing a snippet of proof of concept code.
Now it is time to explore the last-resort scenario, one that is popular with script kiddies but eschewed by sophisticated attackers : denial of service (DoS) attacksin particular, nongeneric attacks against Cisco equipment. We have already reviewed some nongeneric Cisco DoS attacks and, more importantly, the main method of their discoverypacket fuzzingin Chapter 7.
DoS is a type of malicious activity that causes the disruption of service to legitimate users. For our purposes, DoS refers to cutting off the connection to the Internet or other networks, denying the system administrator access to the device, or crashing the device.
As other Hacking Exposed tomes have thoroughly covered DoS attacks, this tome will briefly capture the motives behind such attacks, identify important elements of the DoS, and include some examples of reasonably recent DoS vulnerabilities discovered in Cisco appliances and software. Because a large part of the Internet is powered by Cisco equipment, we think it is necessary to discuss these Cisco DoS- related issues and to show ways of effectively protecting the server, network, or the whole autonomous system against the annihilating results of DoS activities.