Common Unix Vulnerabilities

U1 BIND Domain Name System
U2 Web Server
U3 Authentication
U4 Version Control Systems
U5 Mail Transport Service
U6 Simple Network Management Protocol (SNMP)
U7 Open Secure Sockets Layer (SSL)
U8 Misconfiguration of Enterprise Services NIS/NFS
U9 Databases
U10 Kernel

(From the Twenty Most Critical Internet Security Vulnerabilities
2004
Copyright 2001-2004, The SANS Institute
http://www.sans.org/top20.htm)