Network Security Hacks

Keep an Inventory of Your Network

Use Nmap to keep track of the devices and services on your network.

As we saw in [Hack #40] , Nmap (http://www.insecure.org/nmap/) is free a tool that can be used to conduct various sorts of scans on networks. Normally when people think of using Nmap, they assume it’s used to conduct some sort of nefarious network reconnaissance in preparation for an attack. But as with all powerful tools, Nmap can be used for far more than breaking into networks.

For example, simple TCP connect scans can be conducted without needing root privileges:

$ nmap rigel

Starting nmap 3.48 ( http://www.insecure.org/nmap/ ) at 2003-12-15 17:42 MST
Interesting ports on rigel (192.168.0.61):
(The 1595 ports scanned but not shown below are in state: filtered)
PORT      STATE  SERVICE
7/tcp     open   echo
9/tcp     open   discard
13/tcp    open   daytime
19/tcp    open   chargen
21/tcp    open   ftp
22/tcp    open   ssh
23/tcp    open   telnet
25/tcp    open   smtp
37/tcp    open   time
79/tcp    open   finger
111/tcp   open   rpcbind
512/tcp   open   exec
513/tcp   open   login
514/tcp   open   shell
587/tcp   open   submission
4045/tcp  open   lockd
7100/tcp  open   font-service
32771/tcp open   sometimes-rpc5
32772/tcp open   sometimes-rpc7
32773/tcp open   sometimes-rpc9
32774/tcp open   sometimes-rpc11
32775/tcp open   sometimes-rpc13
32776/tcp open   sometimes-rpc15
32777/tcp open   sometimes-rpc17

Nmap run completed -- 1 IP address (1 host up) scanned in 75.992 seconds

This is tremendously useful for checking on the state of your own machines. You could probably ...