8.3. Evaluating the Tools
An assessment can start by using some form of an information gathering tool. When assessing the entire network, map the layout first to find the hosts that are running. Once located, examine each host individually. Focusing on these hosts requires another set of tools. Knowing which tools to use may be the most crucial step in finding vulnerabilities.
Just as in any aspect of everyday life, there are many different tools that perform the same job. This concept applies to performing vulnerability assessments as well. There are tools specific to operating systems, applications, and even networks (based on the protocols used). Some tools are free; others are not. Some tools are intuitive and easy to use, while others are cryptic and poorly documented but have features that other tools do not.
Finding the right tools may be a daunting task and in the end, experience counts. If possible, set up a test lab and try out as many tools as you can, noting the strengths and weaknesses of each. Review the README file or man page for the tool. Additionally, look to the Internet for more information, such as articles, step-by-step guides, or even mailing lists specific to a tool.
The tools discussed below are just a small sampling of the available tools.
8.3.1. Scanning Hosts with Nmap
Nmap is a popular tool included in Red Hat Enterprise Linux that can be used to determine the layout of a network. Nmap has been available for many years and is probably the most often used tool when gathering information. An excellent man page is included that provides a detailed description of its options and usage. Administrators can use Nmap on a network to find host systems and open ports on those systems.
Nmap is a competent first step in vulnerability assessment. You can map out all the hosts within your network and even pass an option that allows Nmap to attempt to identify the operating system running on a particular host. Nmap is a good foundation for establishing a policy of using secure services and stopping unused services.
8.3.1.1. Using Nmap
Nmap can be run from a shell prompt by typing the nmap command followed by the hostname or IP address of the machine to scan.
nmap foo.example.com |
The results of the scan (which could take up to a few minutes, depending on where the host is located) should look similar to the following:
Starting nmap V. 3.50 ( www.insecure.org/nmap/ ) Interesting ports on localhost.localdomain (127.0.0.1): (The 1591 ports scanned but not shown below are in state: closed) Port State Service 22/tcp open ssh 25/tcp open smtp 111/tcp open sunrpc 443/tcp open https 515/tcp open printer 950/tcp open oftep-rpc 6000/tcp open X11 Nmap run completed -- 1 IP address (1 host up) scanned in 71.825 seconds |
Nmap tests the most common network communication ports for listening or waiting services. This knowledge can be helpful to an administrator who wants to close down unnecessary or unused services.
For more information about using Nmap, refer to the official homepage at the following URL:
8.3.2. Nessus
Nessus is a full-service security scanner. The plug-in architecture of Nessus allows users to customize it for their systems and networks. As with any scanner, Nessus is only as good as the signature database it relies upon. Fortunately, Nessus is frequently updated and features full reporting, host scanning, and real-time vulnerability searches. Remember that there could be false positives and false negatives, even in a tool as powerful and as frequently updated as Nessus.
 | Note |
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Nessus is not included with Red Hat Enterprise Linux and is not supported. It has been included in this document as a reference to users who may be interested in using this popular application. |
For more information about Nessus, refer to the official website at the following URL:
8.3.3. Nikto
Nikto is an excellent common gateway interface (CGI) script scanner. Nikto not only checks for CGI vulnerabilities but does so in an evasive manner, so as to elude intrusion detection systems. It comes with thorough documentation which should be carefully reviewed prior to running the program. If you have Web servers serving up CGI scripts, Nikto can be an excellent resource for checking the security of these servers.
| Note |
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Nikto is not included with Red Hat Enterprise Linux and is not supported. It has been included in this document as a reference to users who may be interested in using this popular application. |
More information about Nikto can be found at the following URL:
8.3.4. VLAD the Scanner
VLAD is a vulnerabilities scanner developed by the RAZOR team at Bindview, Inc., which checks for the SANS Top Ten list of common security issues (SNMP issues, file sharing issues, etc.). While not as full-featured as Nessus, VLAD is worth investigating.
| Note |
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VLAD is not included with Red Hat Enterprise Linux and is not supported. It has been included in this document as a reference to users who may be interested in using this popular application. |
More information about VLAD can be found on the RAZOR team website at the following URL:
8.3.5. Anticipating Your Future Needs
Depending upon your target and resources, there are many tools available. There are tools for wireless networks, Novell networks, Windows systems, Linux systems, and more. Another essential part of performing assessments may include reviewing physical security, personnel screening, or voice/PBX network assessment. New concepts, such as war walking — scanning the perimeter of your enterprise's physical structures for wireless network vulnerabilities — are some emerging concepts that you can investigate and, if needed, incorporate into your assessments. Imagination and exposure are the only limits of planning and conducting vulnerability assessments.