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Using Snort Stealthily
jukal writes "Linux Journal has an article on using Snort as stealth sniffer, a stealth NDIS probe and stealth loger -- on a network interface with no IP address. 'Snort is a versatile and powerful tool for sniffing, intrusion detection and packet logging. Configuring it to run stealthily in sniffing mode or NIDS mode is easy; incorporating it into a stealth-logging solution is only slightly less so'"
It's easy to remain undetected with a custom patch cord, (no transmit). IIRC, 10BaseT, you simply didn't set up the TX wires, and 100BaseT, you untwisted one of the twisted pairs.
It's even possible to remain undetected with software only, but you *really* need to know what you're doing. Stuff can be detected on the ethernet layer that most people aren't aware of.
Unfortunately, firewalls are not the be-all and end-all of network security... A firewall can effectively protect your network from malicious access from the outside world, however it can not prevent hack-attacks on your systems which originate from within your network.
There are two primary reasons for hack-attacks originating inside a firewalled-zone:
1. A trojaned system, usually due to poor Antivirus policy and/or poor user education.
2. A Disgruntled employee who is out to get you!
Obviously, the best solutions to these problems are to implement a good Antivirus product and virus protection policy, and to keep your employees happy!
Unfortunately, no matter how hard you try, there are always likely to be problems you have not forseen - which is where Sniffers and NIDS tools come in. Whilst these tools are also not the sole answer to anyone's prayers, they can often help as part of an overall security system implementation.
Snort is (IMHO) one of the best NIDS tools out there - I have used Snort for a couple of years as part of an integrated security solution, and the logfiles it generates, once properly parsed, have helped me track down a number of threats to network security, and plug any holes present before the problems became serious.
Firewalls are not a panacea, nor are NIDS tools, used together though, they are much more than the sum of their parts....
Disclaimer: I meant what I thought, not what I wrote! What? You can't read my Mind? Oh dear!
The biggest problems are:
- A switch can mangle the packets a little before they're port-mirrored
- How exactly DOES one monitor >100mbit full-duplex traffic using only a single 100mbit port
:) ? (dropped packets are a significant reality on a busy network)
'Course, what you REALLY need is a good, *electrically* transparent impedance matching tap, like one of these.Don't sweat the petty things. But do pet the sweaty things.
Whew, the ISS marketing guys really did a number on your mind, didn't they?
I worked on intrusion detection at a site where we had two IDS systems set up in parallel, one based on RealSecure and the other being a custom tailored solution that utilized a "sensor" machine sitting in our DMZ with a quiet NIC, similar to what's described in the linked article. It used tcpdump for data collection, and saved most of our incoming and outgoing network traffic to a fast disk array for analysis (based on tcpdump filters.) Hourly scripts would process the saved packages with Snort (and a variety of other tools, some of them free and some of them custom written for us and the other sites on our WAN.)
While RealSecure is fine for detecting bumbling script kiddies and obvious misconfigurations (like unpatched boxes becoming Nimda zombies), the tcpdump solution was far better at detecting the serious intrusion attempts, like the slow and low network probes with custom crafted packets, and telling us exactly who on our network was doing boneheaded things like using telnet across network boundaries. RealSecure's coming in a pretty box and costing a lot of money doesn't make it the end-all be-all of intrusion detection systems.
The best analogy for defending your networks is a castle. Castles have moats, walls and an inner keep, all to protect the treasures of the kingdom (jewels, the princess, etc.). But, none of that does you any good without sentries watching the moat and walls who can report to the Captain of the Watch anything out of the norm. Your network defense should consist of a hardened router(the moat), firewall and DMZ (walls), and your private networks (the keep). You should have intrusion detection systems, syslogs from routers and firewalls and regular system monitoring (sentries). All of this should be parsed by a system that provides alerts for key events (report to the Captain of the Watch) and is also checked regularly by humans.
In my universe I'm perfectly normal, it's not my fault you don't live in my universe.
There's a better article about SNORT and ACID on LinuxWorld. Also, if you want to investigate SNORT, check out the following links:
In my universe I'm perfectly normal, it's not my fault you don't live in my universe.
The wonderful tool which is less configurable than Snort, doesn't log data as well, and provides less viewable data about packets which set off alerts.
And this is better than Snort how? Snort can log to local or remote databases, text files, syslog, and probably other formats (but I haven't tried). It supports multiple output formats, so you can choose how you want to look at the data. It also supports loading a database from tcpdump files (Our training with ISS never covered how to do this with RealSecure, and I'm doubtful that it can be done).
Superior in what way? It costs more than Postgres or MySQL, has more holes than any other database out there, and costs an insane amount of money compared to what most people running Snort would use (we use MySQL here, I know many people using Postgres, or you can dump to text files).
In the world of real security grunts, we like to call such a tool Nessus (http://www.nessus.org/). It scans for more vulnerabilities than ISS (the marketing claims by ISS notwithstanding), is updated more frequently, offers more flexibility in scanning options, has a better support community, and is free.
Unfortunately for me, ISS has brainwashed many, many people in the Department of Energy. I'm forced to use their product on a day-to-day basis. On the upside, I can run Snort and Nessus to do all my real checks and detects, and the go to the ISS products I have to use, try to make them show me the data I need, and report with that. But every single site I have to deal with which uses ISS has done the same thing I've done - shoved it in a corner, set up a system with Snort and a system with Nessus, and gone about getting real work done with free, easy to use, well supported tools.
RagManX
You probably should work in the security world before making statements about things you clearly don't understand. tcpdump is a tool for watching all or select traffic. It dumps raw packets, and you have to figure out what to make of them. Snort is a tool for analyzing those packets and alerting on suspicious data. It provides the information you need to help you find potentially dangerous traffic.
Where I work, we have a T-3 'net connection. We typically run about 40% available bandwidth. You'll have just a *TINY* bit of trouble keeping up with that traffic if you manually analyze tcpdump logs. If you run Snort, it will do the bulk of the work, and alert you on things it thinks bear further investigation. It makes mistakes. But having it help focus your traffic checks makes the day a lot easier.
As for using a firewall, too many people have the mistaken impression that once they install a firewall, all their worries will go away. If you have an insider attacking one of your corporate servers, a firewall doesn't help with that at all. An intrusion detection system like Snort will. If you users bring in discs from home that contain trojan programs with call home features, your firewall probably won't catch that, but an intrusion detection system probably will. If your users are surfing to pr0n sites, your firewall might catch that, but an intrusion detection system has a much greater chance.
A firewall is a good thing to have, but everyone working in the security field is going to tell you that it is not enough. We have a concept which we frequently preach to newbs - defense in depth. Put as many systems in place for securing your network as you can realistically manage and track. If you have only a single security device, once an exploit comes out for that device, your network is wide open. And every single security system out there has bugs, so depending on one greatly increases your chances of getting 0wnzerized. Put in multiple systems, and you are likely to catch attacks on at least one of them, in the event that a way to avoid one part of your defense is found.
RagManX
A 10baseT patch cable with the TX wires clipped will get you a whole lotta nothing because the TX wires are used for heartbeat signals. You need to corrupt the outgoing frames instead, which is a PITA.
l #receive-only or read up on Antisniff (weird, I can't find anything about it on @stake's site).
The easier method is to use a 10 Mbit AUI adapter with the TX pins cut. You can probably even find a 10baseT -> AUI adapter at a computer junk shop for a buck or three.
For more about creating a receive-only ethernet adapter check out http://www.robertgraham.com/pubs/sniffing-faq.htm
Why can't I moderate something "Wrong" or at least "Grossly Misinformed"?