If you're looking for a vulnerability scanner, chances are you've come across a number of very expensive commercial
solutions with long lists of features and benefits. Unfortunately, if you're in the same situation as most of us, you simply don't have the budget to implement these fancy systems. You might have considered compromising by turning to free tools like SATAN or Saint. However, you probably saw these tools as a compromise, as their feature sets didn't quite match the commercial solutions'.
It's time that you give Nessus a look! This free tool offers a surprisingly robust feature set and is widely supported among the information security community. It doesn't take long between the discovery of a new vulnerability and the posting of an updated script for Nessus to detect it. In fact, Nessus takes advantage of the Common Vulnerabilities and Exposures architecture that facilitates easy cross-linking between compliant security tools.
The Nessus tool works a little differently than other scanners. Rather than purporting to offer a single, all-encompassing vulnerability database that gets updated regularly, Nessus supports the Nessus Attack Scripting Language (NASL), which allows security professionals to use a simple language to describe individual attacks. Nessus administrators then simply include the NASL descriptions of all desired vulnerabilities to develop their own customized scans.
Nessus uses a modular architecture consisting of centralized servers that conduct scanning and remote clients that allow for administrator interaction. The Nessus server is currently available for a number of Unix/Linux operating systems including FreeBSD, GNU/Linux, NetBSD and Solaris. The client is available for any Unix- or Windows-based operating system. It's important to note that the fact that the server is Unix-based doesn't limit the extent of the systems that may be scanned. NASL descriptions exist for a large number of Windows vulnerabilities, and the tool is extremely powerful for use even within a Windows-only environment.
If you're looking for a robust, inexpensive (free!) vulnerability scanning solution, you should definitely take Nessus out for a test drive!
About the Author
Mike Chapple, CISSP is an IT Security Professional with the University of Notre Dame. He previously served as an information security researcher with the National Security Agency and the U.S. Air Force. Mike is a frequent contributor to SearchSecurity, a technical editor for Information Security magazine and the author of several information security titles including the CISSP Prep Guide and Information Security Illuminated.