nessus report

Paul Schmehl pauls at
Sat Dec 20 23:21:15 UTC 2008

--On December 19, 2008 11:32:51 PM -0600 Richard Yang 
<kusanagiyang at> wrote:

> hi,
> when i ran nessus against my bsd box, nessus can detect "the remote host
> is
> up".
> i don't understand how nessus can detect it...
> does anyone know how it is done?
> thanx

There are several ways to detect if a host is up.  Responses to icmp 
packets is one.  Almost all hosts will respond to pings unless they're 
prevented by a firewall.

Another way is the type of response to a probe of a port.  Sometimes 
services will respond differently if they're firewalled than if they're 
not listening on a particular port.  Also, very few computers have no 
ports at all listening.  For example, most unix boxes will be running 
syslogd and listening on port udp/514.  That is the default for that 
daemon.  Unless you reconfigured syslogd to listen on localhost only, it 
will respond to probes.

Sometimes a host will respond to a problem with RSETs.  It's very, very 
hard to configure a box in such a way that it's impossible to detect that 
it's up and running.

Run sockstat and look at what's listening on your computer.  Then see if 
you can figure out how to get it to stop listening on those ports.

Paul Schmehl (pauls at
Senior Information Security Analyst
The University of Texas at Dallas

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