Nmap – Locating Idle Scan Zombies and FTP Bounce Servers

So, ambulance having read my previous posts on Idle Scanning and FTP Bounce, you may be interested in finding useable boxes.

Now, as I suggested, you could scan for printers or other embedded devices, they make fucking AMAZING Idle Scan hosts. However, there is an nmap script here which is excellent for checking a host to see is it useable, by checking how its IPID sequence works.

Meet ipidseq.nse

ipidseq.nse is basically a test script, that tells you if you can use a host for Idle Scans. So, assuming you want a fair few zombies, lets scan 1000 hosts in the hope of finding a few good ones!

root@bha:~# nmap -iR 1000 —script ipidseq -T5 -v -oA zombies

The above scan will scan 1000 random IP addresses using the ipidseq script, testing them to see are they useable as zombies. I am using T5 here as scanning ranges slowly is BORING :P

The -oA zombies will create three “Output Files”. zombies.xml (XML format of scan), zombies.nmap (normal output), and a third “grepable” version – zombies.gnmap. You can then extract the useable hosts from said list using grep or similar, or just scroll through, copy, paste, like myself…

“So we found us some Zombies. What about those Bouncy FTP servers then?”

Well, nmap again has the solution to this problem. The ftp-bounce.nse script. We will use it in a very similar manner to the ipidseq script…

root@bha:~# nmap -iR 1000 —script ftp-bounce -T5 -v -oA bouncyFTP

This does the same as above, except instead it outputs lists of FTP servers we can “Bounce” via! Useful, no?

BONUS ROUND! Finding Anonymous FTP Servers for stashin’ yo’ warez!

So. Say you want to store/share a bunch of files and need some storage, or just like rummaging through open FTP servers (likely in search of other peoples warez and such… Never know, might find someones super secret 0day stash!).

How do we go about doing such a thing? Well, Guess what? nmap, yet again, solves this problem with the ftp-anon script.

Now, as above, you simply use it like so…

root@bha:~# nmap —script ftp-anon -T5 -iR 1000 -v -oA ftpAnon

Remember – with these you can always scan actual *ranges* instead of my “scan 1000 random hosts” idea, and this is VERY useful for auditing internal networks! Or some specific target networks… I know some web hosting firms may be VERY interested in scanning their own ranges for anonymous FTP setups to detect illegal piracy and such!

Remember, ask before you scan!

Nmap – FTP Bounce Scans

In part One and Two of this series I described various methods of evading IDS/IPS/Firewalls, sick and general methods of evading detection when port scanning your targets using nmap.
In this instalment I hope to give an overview of the technique called the “FTP Bounce” Scan technique, and various “interesting” uses I have had for it…
This, along with my other nmap articles, is all kind of my notes for the wiki article over at http://blackhatacademy.org – reopening soon – with lots of shiny new content and awesome stuff!

So, how does FTP Bounce work?
Well, the File Transfer Protocol, according to its RFC (RFC 959 according to nmap man pages), has a feature called the PORT command (now I may be messing up, but I THINK this is the command. Ping me if I am wrong :3 ). Basically it allows proxy FTP connections, where I can ask the FTP server I am connected to to send a file to a host/port I specify. Obviously, in order to send a file to another host/port, it has to CONNECT to said host/port. So, we can use this to get the FTP server to check is said host/port open… Seeing what I am getting at here?

We can make an arbritary FTP server port scan another server for us (IF said FTP server supports this “feature”… Which, according to nmaps man pages, many do not anymore… but still!).

Now, most of us are likely thinking “Right, so I an make random FTP servers act as “drones” during my port scans… AWESOME!”. Yes, yes you can. This puts another “hop” between you and your victim, meaning it is a shitload harder to trace it back to you! Using standard methods like -T0 and such are recommended here, to make things even sneaker. As the FTP server is not DESIGNED to be a port scanner, it is not exactly going to be stealthy… So we kind of have to rely on timing. Need I say this is TCP ports only also?

Now for the super fun part. Now the following idea, I thought was fairly original when I came up with it while walking my dog. However, upon reading the man pages for nmap (and you wondered why I was sleep deprived? I STILL AM!) I realized Fyodor had gotten there first. Years ago. Feck.
However, it is still a cool trick… So I will outline it.

Say you are scanning company.tld, and have found a FTP server on their network, but the rest of the bloody network is firewalled off. You wish to scan the inside of their network. So, you somehow have gained credentials to their FTP server (or it supports anonymous logins), and you are still wondering how to use this to scan out the insides.
FTP BOUNCE!
Use the external FTP server as your bounce host, and ask it to scan various inside-network ranges (just use the default 10.x, 192.168.x, etc) for you until you figure out which addressing scheme they use. Then ask it to scan the whole bloody network for you! Now, you have mapped out their internal networks by simply leveraging the FTP Bounce bug in their FTP server! Awesome, no?

Using FTP Bounce (Assuming you have a vulnerable FTP that allows this, see the ftp-bounce NSE script for checking FTP servers…)

root@bha:~# nmap -T0 -b username:password@ftpserver.tld:21 victim.tld

This uses the username “username”, the password “password”, the FTP server “ftpserver.tld” and port 21 on said server to scan victim.tld.
If the FTP server supports anonymous logins, just forget about the username:password@ part and nmap will assume it allows-anonymous. You may omit :21 if the FTP port is 21, however, some people configure FTP on wierd ports as an attempt at “security”.

So, thought up of any “fun” uses for the FTP bounce scan technique? Tell us about them! And keep an eye out for the finished Wiki article over at http://blackhatacademy.org (if I ever finish it, that is :P )

// Yay! Still importing content with great success!