Vulnerability scanners are automated tools designed to scan hosts and networks
for known vulnerabilities and weaknesses. There are a number of these tools on
the market. Some are free and others will significantly strain your budget.
Network Associates CyberCop Scanner and Internet Security Systems (ISS) Internet
Scanner are two of the leading commercial scanners in the industry. These tools
essentially perform a series of automated checks against each target, trying to
locate known vulnerabilities. Each tool has a vulnerability signature database
that it can use to test the host for known vulnerabilities. If the vulnerability
does not exist in the database, the tool cannot find it. Additionally, if the
database is not continually updated, the tool will not find the latest
vulnerabilities and will become less effective. Therefore, the number of
vulnerabilities a scanner looks for and the frequency of the updates are
important criteria for selecting the right vulnerability scanner. The problem is
each vendor does not define the term vulnerability in the same way. For
instance, some scanners find one vulnerability and then report each piece of
information that can be gathered as a result of this one vulnerability as
additional vulnerability checks. So a single vulnerability becomes ten as
reported by the scanner.
There are two main types of automated scanners, network-based and host-based. Network-based scanners attempt to look for vulnerabilities from the outside in. The scanner is launched from a remote system such as a laptop or desktop with no type of user or administrator access on the network. Conversely, the host-based scanner looks at the host from the inside out. Host-based scanners usually require a software agent to be installed on the server. The agent then reports back to a manager station any vulnerabilities it finds. Network-based scanners look for exploitable remote vulnerabilities such as IIS holes, open ports, buffer overflows, and so on. Host-based scanners look for problems such as weak file permissions, poor password policy, lack of security auditing, and so on. Host-based and network-based scanners complement one another well. It is very effective to employ both when testing critical systems. Again, you need to be careful when using these scanners. Network-b...
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