Last week, I spent most of my time installing Linux and a few white hat
applications from hacker Web sites: Firewalk, Nmap, Sniffit, Swatch and
Tripwire. This week, I've had a bit of a chance to play around with
This "white hat" nomenclature confused me when I first heard it. White
hat is a fairly common term for people who hack legitimately - security
staff, researchers and so on. By contrast, black hat hackers hack
maliciously. Basically, white hats are the good guys; black hats are
the bad guys. Gray hats are somewhere between the two, and nobody knows
where Red Hat Linux fits in with all this.
I'm told the terms come from the early Western movies. Because the
movies were filmed in black and white, the chase scenes tended to get a
bit confusing, until someone decided to give the good guys white hats
and the bad guys black hats. Anyway, back to Linux. Frills and Thrills
Nmap impressed me. It's simple, it's powerful, and it does exactly what
it says it does: It maps your network. The author, who goes only by the
name Fyodor, even includes a short but well-written HTML manual in a
choice of five languages. The program is freeware, so you've got to
admire the amount of work that he's put into it.
Nmap runs ping sweeps to find out what machines are connected to your
local network, a port scan to find out what services each machine is
running and TCP/IP fingerprinting to find out what operating system
each is running. The result is a log file giving you a reasonably
complete list of what's on your network and what it's doing. That's
useful information both for a security manager and any hacker.
We also run Internet Scanner from Atlanta-based Internet Security
Systems Inc. (ISS). Internet Scanner can do exactly what Nmap can do
and much more. The big difference between the tools - apart from the
fact that Nmap is free and Internet Scanner most certainly isn't - is
the slant each puts on this function.
The ISS tool gives a much more user-friendly graphical user interface
(GUI), advertises its presence to anyone being scanned and so on. It's
clearly designed to fit into a corporate environment.
Nmap, on the other hand, is designed for technical staffers who want to
dispense with the frills: It's much faster, and it's designed to be run
in "stealth mode" so as to avoid detection by intrusion detection
software. It certainly snuck in beneath the radar of our intrusion
detection software, RealSecure from ISS. That's something we'll have to
Sniffing for Hack Attacks
Next up was Sniffit, a network packet sniffer. Packet sniffers are
rather intriguingly named pieces of software that monitor network
Under many networking protocols, data that you transmit gets split into
small segments, or packets, and the Internet Protocol address of the
destination computer is written into the header of each packet. These
packets then get passed around by routers and eventually make their way
to the network segment that contains the destination computer.
As each packet travels around that destination segment, the network
card on each computer on the segment examines the address in the
header. If the destination address on the packet is the same as the IP
address of the computer, the network card grabs the packet and passes
it on to its host computer.
That's how I think it works, anyway. I'm sure there are many network
engineers out there who are champing at the bit to explain the many
subtle but important errors I've made, but frankly, that little model
seems to work for me.
Promiscuous Network Cards
Packet sniffers work slightly differently. Instead of just picking up
the packets that are addressed to them, they set their network cards to
what's known as "promiscuous mode" and grab a copy of every packet that
goes past. This lets the packet sniffers see all data traffic on the
network segment to which they're attached - if they're fast enough to
be able to process all that mass of data, that is. This network traffic
often contains very interesting information for an attacker, such as
user identification numbers and passwords, confidential data - anything
that isn't encrypted in some way.
This data is also useful for other purposes - network engineers use
packet sniffers to diagnose network faults, for example, and we in
security use packet sniffers for our intrusion detection software. That
last one is a real case of turning the tables on the attackers: Hackers
use packet sniffers to check for confidential data; we use packet
sniffers to check for hacker activity. That has a certain elegant
simplicity to it.
I've known of packet sniffers for years, and I've talked about the
dangers of attackers using packet sniffers in many a consulting
assignment, but like many consultants, I've never actually used one
One of the reasons for that is simple fear - I'm not that technical at
the best of times, but networking is by far my weakest subject. So I've
avoided trying packet sniffers because I expected to get swamped by all
sorts of networking jargon and problems that would send me running to
our network support guys. I feel embarrassed enough that I can't get my
head around the concept of subnet masks, so I don't want to display my
greater ignorance if I can possibly avoid it.
The thing that worried me most about Sniffit was how easy it was to
install. It took about three commands and three minutes to get this
thing installed and running on my Linux machine. It even has a GUI (not
exactly pretty, but hey - it's free).
Like Nmap, Sniffit is very easy to use and does exactly what it says it
does: It sniffs your network and shows you what sort of data is getting
I'd recommend that you install a packet sniffer and have a look at what
sort of data you can see on your local network. Better still, get one
of your network engineers to install it for you. They probably know of
better, more professional sniffers and will be able to talk you through
some of the data that you see going past. It's an interesting look into
exactly what's going on within your network.
Firewalk, Swatch and Tripwire stumped me. I don't yet know what I'm
doing wrong, but I can't get these things installed. I may not get
around to it, though, because my long-awaited laptop has finally
arrived. Now, I can get back on course with all those projects that
have been on hold for the past couple of weeks.