The Cisco Discovery Protocol has had a history of vulnerabilities in various IOS products. It is used in Cisco environments for devices to advertise information to other Cisco devices, such as versions and capabilities.
Exploiting this protocol has usually resulted in Denial of Service conditions and required using various programs from less than reputable sources. One notable exception to this is Yersinia.
However, the Metasploit Framework has been distributed with the Racket library, that provides an interface for forging raw CDP frames, provided by Jon Hart. SecureState is releasing a module that allows users to take advantage of this functionality.
The module allows users to set the various parameters of a CDP frame and then transmit it as often as they'd like to transmit. This is useful in situations where a user needs to imitate a Cisco device, such as a VoIP phone.
Within the past year, another CDP bug was discovered in the Nexus line of switches from Cisco by George Hedfors. This bug, which was given the ID CSCtf08873, is triggered when a CDP message is received by the device with a "Device ID" greater than 255 bytes. Hedfors submitted the bug in the summer of 2010, and recently discussed it in his Black Hat EU presentation, "Owning the Data Centre."
To download the CDP tool, go here.