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Fooling NMAP for Whatever Reason
taviso writes "Are you bored with your OS fingerprint? Do you dream of being able to impress your friends by convincing them your webserver is running on a sega dreamcast, or Apple LaserWriter? Well Dream no more! David Berrueta has written a paper oulining the techniques and tools available to defeat nmap's OS fingerprinting, available here [pdf]. Besides the hours of entertainment this could provide, he also lists some of the more serious reasons why you might want to consider this."
I could just see slashdot running on a Trash - 80. .
Modular Redundancy--Because 4 out of 5 Nodes agree
...to see the first time some hacker scans my network to see that every server is running off a Dreamcast. Wouldn't that be funny if that became the secure standard? Every TCP/IP fingerprint returns "Sega Dreamcast". Wouldn't be a huge security boost, but it would help slow down the process of choosing a system to try and break. And the stupid kids who think they're hackers would probably just move on.
Many servers hosting the web site of the US armed forces don't seem to be running the OS they are claiming to run. However, this *could* also be the result of some sort of load balancing.
I've seriouly been looking for this for my home box. Of course its only part of the way of hiding the real OS your running. One part of eunermation is to look at the banners that network servers show. For example telneting to my home box
:). So changing these as well could give those l33t script kiddies some fun :)
[rghf@localhost rghf]$ telnet foo.wibble 22
Trying foo.wibble...
Connected to foo.wibble
Escape character is '^]'.
SSH-2.0-OpenSSH_3.4p1 Debian 1:3.4p1-1
Shows I'm running debian (or am I?
Rus
Cheap UK and US VPS
Well, this proves that it doesn't matter what OS fingerprint you have, you can still get slashdotted...
(But not before I d/led it to my local machine first!)
Well I'm strongly against security through obscurity as a security infrastructure. However, as long as you have a solid, proven security infrastructure protecting your enviornment then adding a bit of obscurity over the top as an added layer can only be benefitial.
If I know that I've done everything to protect my x86 Linux box from an attack if the attacker already knows it's an x86 Linux box, what distro it's running, has access to my network (assuming the attacker is an employee) etc. then why not make it so that script kiddies will think it's a commodore 64 and will try and exploit it as so?
Though security through obscurity is not a good idea as the only form of protection, it can add another blanket of support and I'm all for that as long as you understand what you're doing and why.
The folks at netcraft use these kinds of techniques for getting their server stats. Modifying the TCP/IP stack will screw up their stats collection :(
OS fingerprinting is dying!
(sorry. someone had to...)
Well, not me personally. But what do you think Microsoft has been doing all the years? Considering how stable their site is (and taking into account the humongous crash when they tried to move Hotmail onto WinNT), I'm convinced that they've been running the whole MSN network on Unix-based servers, disguising them as Windows ;)
$x='S24;r)>63/* h@<5+oZ)32"5cz';$me='phroggy'x$];
$x=~y+ -xz+\0-Tx+;print$_^chop$me for split'',$x;
Quoting from "Microsoft IIS 5 Administration" ) pp 52) ...
Longwinded way of saying Unix/Linux is percieved as being harder to crack. :)
Do you even lift?
These aren't the 'roids you're looking for.
A lot of sites have to eat their own dogfood, like hotmail. Now they needn't any longer. If they can change their fingerprint, they can run linux and make it look like they're running NT. (They used to run FreeBSD earlier.)
Someone thought about OS fingerprint obfuscating a while ago... http://ippersonality.sourceforge.net/
Because someone using TCP/IP fingerprinting is looking for interesting hosts to attack, for whatever reason.
Something they've never seen before is interesting, and the would be hacker would likely pry a bit deeper. Giving them false information either makes them disinterested ("some idiot put up a Dreamcast on the web, how stupid") or leads them to attack in a way you are expecting, and that you know will be ineffective. Watching for these known false attacks could act as some part of an early warning alarm system, holding the attacker with his interest long enough to track him down. Ala, the Cuckoo's Egg.
Yessiirreee,
I'm servin' mah HTTP files from this here ol' guitar and my FTP files from an empty bottle-a-booze.
And this post, yes HTTP_REFERER was from the ol' cadillac factory I once worked at; the one where I snagged my dancin' machine car one peice at a time over twenty or some number of years-*HICUP*
-SlashdotTroll (because slashdot don't like me, my karma is terrible, and at -1 they only let me post twice in 24hours from this ol' Folsom prison I'm stuck in.)
... a story i heard a while back regarding script kiddies.
some researchers set up a unix server, went into a script kiddies irc channel and said they found this wide open windows box, saying it contained credit card numbers or something like that, giving the ip of their honeypot.
not one kiddie tried a unix sploit on the box, 100% of the attempts were exploits designed for windows.
so for fooling nmap, if you're a security admin, set up your windows boxen with unix fingerprints and vice/versa, and you'll at least avoid getting r00ted by most script kiddies. just continue to be aware of the dedicated cracker whose above the ranks of kiddies.
The One Rule Of Chess You'll Ever Need: Don't play someone who carries a kit in their bookbag.
Here.
:-X
Please mod this down so I don't get slashdotted too badly.
$x='S24;r)>63/* h@<5+oZ)32"5cz';$me='phroggy'x$];
$x=~y+ -xz+\0-Tx+;print$_^chop$me for split'',$x;
I've seen very few portscans against any of my internet connected boxes. The usual unsolicited connection attempts tend to be for well-known exploits (18 months ago, port 111 was *really* popular with several attempts a day). I'm not really sure whether it's worth the effort going out of your way to do things to change the OS fingerprint that nmap comes up with (even under good conditions, I've never found nmap's fingerprint particularly reliable or accurate anyway)
Oolite: Elite-like game. For Mac, Linux and Windows
If their computers start lying about their OS and software installed then the BSA will invade them and stick 100 lawyers on their head before you can say "Nmap"
A caveman dreams of being us, the incalculable power and riches. We dream of being Q, then what?
Any level of additional security, brought about by "lying" or "fooling" is a great thing. After all, nobody needs to know your OS except you. But my opinion is that people should keep their faked responses within the realm of reason. No Sega Dreamcasts, no TI calculators, no Epson Dot Matrix LQ-2170 printers... If you lie, it must be a believable lie or it will be transparently obvious and the h4x0r will figure it out instantly. And that's not a security boon at all.
Takes a completely different approach to what I was thinking - I was thinking of doing it all in userspace. Run some daemon that uses libpcap and "responds" to certain ports like a real machine. Basically means a TCP stack in userspace, so it's not a trivial undertaking but still lots of fun. I was also thinking of making it use nmap's own configuration files so you can simply specify what OS you want it to look like and it looks up the params in the config file. Only disadvantage is that you want it to pass "real" packets in to the kernel for normal processing so this is only useful in limited situations (when you can firewall a machine off completely from the Internet and only need it to serve up something within your organization). I was also considering writing something that uses FreeBSD's divert sockets since you could integrate that nicely with your firewall, but it wouldn't be as portable as the other approach (which would work wherever pcap works).
Anyway, this has been done. The paper seems slashdotted so I can't read it.
From the Netcraft FAQ:
Why do you report impossible operating system/server combinations ?
Webservers that operate behind a caching system, load balancer, reverse proxy server or a firewall may sometimes report the operating system of the intermediate machine. Hence reports of 'Microsoft/IIS on Linux' may indicate that either the web server is behind a Linux server that is acting as a reverse proxy, or has configured the Akamai caching system such that the first request to the site goes to one of Akamai's servers [which run Linux], or as in the case of www.walmart.com has been configured to send a misleading signature.
Well I'm strongly against security through obscurity as a security infrastructure. However, as long as you have a solid, proven security infrastructure protecting your enviornment then adding a bit of obscurity over the top as an added layer can only be benefitial.
Yes, except you are implementing this security by fucking with your tcp/ip stack. In other words, you are taking the 'solid, proven security infrastructure' and stirring it up a bit. It is no longer proven to be solid so this bit of obscurity could have cost you some real security. Personally this is not a patch I'd go applying to production machines.
dan.
I wonder how clever this deception is? It's easy enough to grab the version advertisement, but more difficult to make your system respond the same way as another OS, especially if that other OS is 'broken' in regard to TCP/IP. The question is whether you want to mimic the 'bug for bug' behaviour...
There are some who disable ICMP response because it could help to show that a machine is active. Well, that's the canonical reason. But you can also use ICMP to (very slowly) move data, so at least in a far-fetched scenario it could be used a vector for attack.
Say someone wants to attack your server. NMAP shows the OS as Windows NT. However, attaching to port 80 shows an Apache version string that has been released with RedHat. The casual cracker may have been deterred by the OS advertisement, but anyone else would not have. If your defense depends to a large part on version obfuscation then you don't have a defense, simply put.
So you could grep through all the sources for version strings of all your internet exposed services, but that won't gain anything. Does version obfuscation hurt? Probably not. Neither does changing your user-agent string in the browser, except that fewer non-IE browsers will be tallied. For this reason alone I don't change my user-agent string, nor do I change my OS signatures (though I know how to).
honeyd is able to do this already for quite a long time. With honeyd you can basically create "virtual hosts", running on another computer, with their own IP address, their own IP personality (it comes with a large database of them), and their own services (basically, every inetd-capable program can be used as server with it). You can even create a "virtual network" of them, with configurable routes, latency and packet loss. Indistinguishable from real computers and networks.
A monkey is doing the real work for me.
ObReadTheArticleFirst:
"IP Personality
The first and probably, best option is IP Personality. It'a netfilter module (then, only available for 2.4 linux kernels) that allows us to change the IP stack behaviour and 'personality', having multiple network personalities depending on parameters that you can specify as an iptables rule. "
etc, etc, etc..
Support FSF: Stop thinking with your wallet, and think with your imagination. (cc/non-commercial)
Keep going and soon you'll have an empty route table. Do you drop just the IP or the class C or the entire netblock?
Unless it is an all out attack, I just report it to the netblock owner. Most of the time (almost always) the report goes ignored and unanswered.
No sig
He telneted to port 22, the ssh port. He used telnet so you could see the informational banner.
I was one of the instructors in the war games lab. To make things interesting for the students, I distributed nmap with a modified nmap-os-fingerprints file. Windows 2000 machines were reported as Solaris 2.6 (X86) and so forth. Some of the student responses were interesting.
I want to drag this out as long as possible. Bring me my protractor.
This is cool and all, but these days worms and virii select victims at random so your fingerprint won't make a damn bit of difference, except you might think you are a bit safer but you are not.
Silly Rabbit: tricks are for kids.
I read this article a few days ago and bookmarked most of the links I thought valueable. If anyone else is interested add some more to this thread so I can grab them :)
a rticle.txt
Exported bookmarks Fingerprint
blackhole(4) - a sysctl(8) MIB for manipulating TCP
Help Net Security OS-FngrPrint article in PDF
Honeyd - Network Rhapsody for You
http://ojnk.sourceforge.net/stuff/iplog.readme
http://www.insecure.org/nmap/nmap-fingerprinting-
IP Personality - Home
Kernel Options
p0f file listing
PhoneBoys FireWall-1 FAQs: Blocking queSO packets
s0ftpr0ject 2000 Fingerprint Fucker
Security Technologies
SourceForge.net: Project Info - SING
Sys-Security.com - Because Security is not Trivial
USENIX Technical Program - Abstract - Security Symposium - 2000
-- "of course thats just my opinion, I could be wrong." --Dennis Miller
As for the paper, I found it interesting and amusing enough to announce to the nmap-hackers. I'm all for doing this to your personal machines for entertainment and experimental value, but would almost never recommend it as a serious security hardening technique. Your time is almost always better spent working on fundamental security improvements such as applying patches, tightening firewalls, installing IDS systems, removing unnecessary services and setuid binaries, auditing system logs, etc. And sometimes this type of spoofing can actually increase security risk. Nmap expects many modern UNIX operating systems to offer nearly-unpredictable generation of TCP initial sequence numbers and the IP ID field. Crippling the generators to appear as a printer can make you vulnerable to TCP connection spoofing and a plethora of vulnerabilities related to the new Nmap Idle Scan technique.
And remember that many or most worms and script kiddies simply spew their exploit code to every listening server rather than bothering with fingerprints. All the attempted IIS exploits in my Apache log are testament to that! And if you attract a more competent attacker, you probably won't fool them for long anyway.
-Fyodor
Concerned about your network security? Try the free Nmap Security Scanner
So ractically speaking, 99.999% mundane risks (kiddies, scripts, worms) out there do minimal OS detection, and pretty much shoot attacks at random IP's. Those that do some form of detection before trying to attack certainly aren't using NMAP to scan (server version detection is far more common, and is not limited to version strings.
For my money the time spent on stack-signature obfuscation would be far better invested in actual security measures (e.g. staying up to date on patches, implementing defense-in-depth or deploying hardened OS's.
Sure, if you're going to put your servers behind a load ballancer, packet filter or proxy, then you may well get a measure of obfuscation for free, but if the security implementation on the screened systems is no good you're going to get rooted anyway.
Linux is Linux, if One need clarify their dist: <Dist>/GNU Linux
bsds are of course just BSD
If you use NetCraft to see what Iowa State is running, it says they are using /bin/sh as their webserver. Here are the results.
Is this related? How do they do that? It must be a joke.
The systems described in the paper such as IP Personality and Honeyd (my favorite), work by watching for the exact probes as described in my fingerprinting paper and then responding as detailed in the Nmap OS DB. But what about all the other TCP/IP techniques for fingerprinting a system? Later this year, I hope to add about half a dozen, including selective ACKs, TTL-normal-reply, and TTL-RST-Echo. Once these are implemented, spoofed systems will appear as a Dreamcast (or whatever) using the old techniques and will be exposed as their real OS via the new techniques. So Nmap could offer fingerprints like "Linux 2.4 pretending to be a Laserwriter". And attackers could even scan the 'Net looking for spoofed boxes -- lets hope the spoofing modules/programs don't open any security holes of their own!
Of course, the spoofers will then update their software to recognize the new fingerprinting technique and the cycle begins anew. Ah well. I enjoyed Berrueta's paper, by the way.
-Fyodor
Concerned about your network security? Try the free Nmap Security Scanner
I can always telnet to a UNIX box - regardless if you remove telnetd or not.
It just that I have to use another port
I've sent email and surfed the web using telnet !
Telnet us very usefull to debug a port with a text protocol...
However it's not a secure way to log in to a box!
Just saying it like it are.
For a while now, Netcraft has reported Wal-Mart as running IIS 5.0 on Linux or Solaris :) See for yourself
political_news.c: warning: comparison is always true due to limited range of data type