||This article needs additional citations for verification. (February 2013)|
|Developer(s)||Tenable Network Security|
|Stable release||5.0.2 / October 9, 2012|
|License||Proprietary; GPL (2.2.11 and earlier)|
|Website||Nessus Vulnerability Scanner Homepage|
In computer security, Nessus is a proprietary comprehensive vulnerability scanner which is developed by Tenable Network Security. It is free of charge for personal use in a non-enterprise environment. Its goal is to detect potential vulnerabilities on the tested systems.
According to surveys done by sectools.org, Nessus is the world's most popular vulnerability scanner, taking first place in the 2000, 2003, and 2006 security tools survey. Tenable Network Security estimates that it is used by over 75,000 organizations worldwide.
Nessus allows scans for the following types of vulnerabilities:
- Vulnerabilities that allow a remote hacker to control or access sensitive data on a system.
- Misconfiguration (e.g. open mail relay, missing patches, etc.).
- Default passwords, a few common passwords, and blank/absent passwords on some system accounts. Nessus can also call Hydra (an external tool) to launch a dictionary attack.
- Denials of service against the TCP/IP stack by using mangled packets
- Preparation for PCI DSS audits
In typical operation, Nessus begins by doing a port scan with one of its four internal portscanners (or it can optionally use Amap  or Nmap ) to determine which ports are open on the target and then tries various exploits on the open ports. The vulnerability tests, available as subscriptions, are written in NASL (Nessus Attack Scripting Language), a scripting language optimized for custom network interaction.
Tenable Network Security produces several dozen new vulnerability checks (called plugins) each week, usually on a daily basis. These checks are available for free to the general public; commercial customers are not allowed to use this Home Feed any more. The Professional Feed (which is not free) also give access to support and additional scripts (e.g. audit files, compliance tests, additional vulnerability detection plugins).
Optionally, the results of the scan can be reported in various formats, such as plain text, XML, HTML and LaTeX. The results can also be saved in a knowledge base for debugging. On UNIX, scanning can be automated through the use of a command-line client. There exist many different commercial, free and open source tools for both UNIX and Windows to manage individual or distributed Nessus scanners.
If the user chooses to do so (by disabling the option 'safe checks'), some of Nessus' vulnerability tests may try to cause vulnerable services or operating systems to crash. This lets a user test the resistance of a device before putting it in production.
Nessus provides additional functionality beyond testing for known network vulnerabilities. For instance, it can use Windows credentials to examine patch levels on computers running the Windows operating system, and can perform password auditing using dictionary and brute force methods. Nessus 3 and later can also audit systems to make sure they have been configured per a specific policy, such as the NSA's guide for hardening Windows servers.
The "Nessus" Project was started by Renaud Deraison in 1998 to provide to the Internet community a free remote security scanner. On October 5, 2005, Tenable Network Security, the company Renaud Deraison co-founded, changed Nessus 3 to a proprietary (closed source) license. The earlier versions appear to have been removed from the official website since then. The Nessus 3 engine is still free of charge, though Tenable charges $100/month per scanner for the ability to perform configuration audits for PCI, CIS, FDCC and other configuration standards, technical support, SCADA vulnerability audits, the latest network checks and patch audits, the ability to audit anti-virus configurations and the ability for Nessus to perform sensitive data searches to look for credit card, social security number and many other types of corporate data.
The Nessus 2 engine and a minority of the plugins are still GPL, leading to forked open source projects based on Nessus like OpenVAS and Porz-Wahn. Tenable Network Security has still maintained the Nessus 2 engine and has updated it several times since the release of Nessus 3.
Nessus 3 is available for many different Unix-like and Windows systems, offers patch auditing of UNIX and Windows hosts without the need for an agent and is 2-5 times faster than Nessus 2.
On April 9, 2009, Tenable released Nessus 4.0.0. On February 15, 2012, Tenable released Nessus 5.0.
See also 
- Penetration test
- Metasploit Project
- Security Administrator Tool for Analyzing Networks (SATAN)
- SAINT (software)
- Snort (software)
- "Nessus 5.0.2 Available". Retrieved 2012-11-09.
- "sectools.org". Retrieved 2009-10-21.
- LeMay, Renai (2005-10-06). "Nessus security tool closes its source". CNet.
- Carey, Mark; Russ Rogers, Paul Criscuolo, Mike Petruzzi. Nessus Network Auditing. O'reilly. ISBN 978-1-59749-208-9.
- "Nessus feed letter".[dead link]
- "OpenVAS". Retrieved 2009-10-21.
- "Nessus 3 documentation".