Exploiting Cisco Routers

Cisco routers are everywhere. In fact, most network architectures are built on Cisco routers. It is because of this ubiquity that security researchers (white-, gray- or black-hat's) look to these boxes for network penetration testing and access.
An (older, but still applicable, sadly) well-written article by Mark Wolfgang for Security Focus highlights exploitation of vulnerabilities and poor configurations in Cisco routers.

Take a read.