War Tools! Scan, Sniff, Spoof and Hijack

Published: Oct 16, 2002
Updated: Oct 16, 2002
Section: Network Security Library :: Harmless hacking book
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[Free Dmitry Sklyarov] [Advertisement] [Free Dmitry Sklyarov] ___________________________________________________________ GUIDE TO (mostly) HARMLESS HACKING Vol. 3 No. 9, Part 1 War Tools! Scan, Sniff, Spoof and Hijack ____________________________________________________________ This Guide is excerpted from the Second Edition of “The Happy Hacker” book, available Sept. 31 1998. “Hello, I don’t mean to be rude, but I noticed you were examining something, er... proprietary on our system. Would you mind explaining what you were doing?” Sigh. From time to time I get an email like that. Sometimes it is less polite than this. In this case, I had been examining an intranet server. For some reason it was directly accessible from the Internet instead of being on a private internal network. I’ll bet you can’t reach that box from the Internet any more:) I was just curious, not trying to break in! The one thing that defines a hacker is curiosity: a blinding, insatiable hunger for more, more, more information. If your objective is to fight those who attack your computers, your curiosity will be your greatest asset. This chapter covers some powerful war tools that can satisfy your curiosity in a legal and constructive way -- and shows how to use them to battle computer criminals. Sysadmins tell me that it is far harder to keep people out of your computer systems than it is to break in. In this chapter we will get a glimpse of this war between sysadmins and computer intruders, and learn something about the tools they both use. ******************* In this chapter you will learn about: IP address scanning Port scanning a beginner’s scanner a stealth scanner How to give intruders a hard time Nuke Nabber (for casual users) Port Dumper (for anyone with a sense of humor) RotoRouter (drive the bad guys nuts) Sniffit TCPview TTY-Watcher (great fun for casual users, great tool for sysadmins) Industrial strength tools Etherpeek IP-Watcher T-sight **************** ********************************* You can get punched in the nose warning: Before you start playing with the techniques of this chapter, beware. If you use what you learn here for snooping on other people’s networks, you should expect them to suspect you of being a computer criminal. For this reason, if you want to explore other people’s systems, it helps to make friends with the staff of your ISP so they won’t kick you off for suspicion of computer crime. Also, it helps to get permission from the sysadmins of whatever network you are checking out. If you find a problem, you should notify the responsible sysadmin so he or she may fix the problem. It also helps to maintain a good reputation. If you are known as a troublemaker, you will get lots of grief for using the tools of this chapter. If you have a good reputation, people will believe it when you say you are exploring in order to learn network administration -- or simply for the pure joy of discovery. If your ISP is one of those big, anonymous places that would kick you off at the least sign of trouble, switch to a local ISP where you can drop in and offer to take the tech support staff out for pizza. Trust me on this, if you try out what this chapter teaches, almost any large ISP will soon give you the boot. ********************************* ********************************* You can go to jail warning: If you live outside the United States, be sure to check on what the local computer crime laws are. I can’t guarantee the tactics of this chapter will be legal everywhere. ********************************* IP Address and Port Scanning Every day someone emails me to complains that some host name in an ancient GTMHH won’t do cool stuff any more. Imagine that! When I wrote those first GTMHHs I was just sending them to a few friends. I assumed these Guides would soon fade out of existence in the vastness of the Internet. Little did I suspect that eventually tens of thousands of newbies would be fingering, telnetting, ftping, phfing and worse into those IP addresses. So of course their sysadmins have buttoned them down. Strangers can’t play with them any more. What really saddens me is how many people ask me for good host names they can use. It is so easy to find them yourself! If you want to be primitive about it, you can scan for IP addresses by hand. Find a tempting domain name while surfing the web, running traceroute or tracert, or in the headers of email. Then try the techniques of the “Port Surf’s Up!” chapter to see if there is anything interesting there. This is a good way to start, because you know exactly what you are doing and can get a gut feel for the process. Also, it’s quite a rush to discover something rare like the Internet backbone VAX/VMS in the port surfing chapter -- and discover that it is advertising the status of its huge network to you from port 15! There also are programs that will find live Internet host computers for you automatically. Many of these tools will also map which ports are open. They won’t always give you all the goodies you can get when you port surf by hand, but they find out the basics for you fast. ******************************** You can get punched in the nose warning: The downside of the IP scanner and port scanner tools of this chapter is that when you use them on other people’s computers without permission, this practically shouts “I am a criminal hacker.” Presumably this isn’t true, but way too many sysadmins have discovered that a port scan is soon followed by a break-in attempt. If you do insist on scanning without permission, it helps to scan Internet hosts owned by other hackers. If people who are obviously hackers complain, the sysadmins at your ISP or company LAN may not have much sympathy for them. Hey, they are hackers, they can take care of themselves. However, if you do this without the hackers’ permission, you just might incite a hacker war against you, which may nevertheless lead to losing your Internet access. ******************************** So we’re ready to scan for Internet hosts and their ports. Let’s start with how newbies can do it. You can get a Windows 95/98 program that scans IP addresses and ports, What’s Up Gold, from http://www.ipswitch.com. It’s free for a one month trial. It’s a simple point and click program that does an excellent job. Here’s what I get when I scan IP addresses from 198.987.999.1 through 198.987.999.254 looking for any open ports in the range of 1 through 600. This scan is set to check each port by waiting only 100 milliseconds for a response from each one: 198.987.999.033 198.987.999.036 80 198.987.999.044 198.987.999.048 198.987.999.049 198.987.999.066 198.987.999.067 198.987.999.074 198.987.999.080 198.987.999.113 198.987.999.115 198.987.999.118 198.987.999.167 I run the same scan again but with the time-out set to 1 second. This reveals many more live IP addresses and ports: 198.987.999.033 7 9 11 13 15 19 21 23 25 37 53 79 80 110 111 113 139 143 198.987.999.034 139 198.987.999.035 198.987.999.036 80 139 198.987.999.041 198.987.999.042 139 198.987.999.043 139 198.987.999.044 139 198.987.999.045 139 198.987.999.048 139 198.987.999.049 139 198.987.999.050 80 139 198.987.999.051 21 22 23 25 37 70 79 109 110 111 113 143 198.987.999.055 139 198.987.999.056 198.987.999.058 139 198.987.999.059 139 198.987.999.060 198.987.999.061 139 198.987.999.061 139 198.987.999.065 139 198.987.999.066 21 23 80 139 198.987.999.067 198.987.999.068 198.987.999.069 198.987.999.072 198.987.999.073 198.987.999.074 198.987.999.075 198.987.999.077 198.987.999.078 198.987.999.079 198.987.999.080 198.987.999.082 198.987.999.083 198.987.999.084 198.987.999.085 198.987.999.086 198.987.999.088 198.987.999.092 198.987.999.093 198.987.999.098 198.987.999.099 198.987.999.101 198.987.999.103 198.987.999.105 198.987.999.108 198.987.999.110 198.987.999.111 198.987.999.112 198.987.999.113 198.987.999.115 198.987.999.118 198.987.999.119 198.987.999.120 198.987.999.121 198.987.999.122 198.987.999.123 198.987.999.124 198.987.999.125 198.987.999.126 198.987.999.131 198.987.999.133 198.987.999.136 198.987.999.137 198.987.999.139 198.987.999.146 198.987.999.156 80 198.987.999.158 198.987.999.162 139 198.987.999.163 198.987.999.165 198.987.999.166 198.987.999.167 198.987.999.169 7 9 13 198.987.999.173 13 15 21 23 25 79 513 514 515 540 198.987.999.177 198.987.999.178 135 389 198.987.999.180 198.987.999.182 198.987.999.183 198.987.999.184 198.987.999.186 139 198.987.999.188 198.987.999.189 139 198.987.999.194 139 198.987.999.195 7 9 13 17 19 135 139 198.987.999.198 110 119 139 OK, I admit it, to save space I was trying to accomplish two slightly conflicting things with this particular set of IP addresses. These are (foobarred) dynamically assigned IP addresses of an ISP. These are assigned to dial-up customers. So some of these addresses will change or the users of the same address may change from one scan to the next. However, these two scans were done only a few minutes apart. So not many of the connections would have changed in this period. These scans show the importance of a long time-out setting in What’s Up. One second (1000 ms) has given me better results. Here, among these dynamically assigned IP addresses, is where I really get my kicks. Dynamically assigned IP addresses are the Rick’s Cafe -- no, the Star Wars Cantina -- of cyberspace. OK, most of these IP addresses reveal no open ports. They are probably mere dialups for downloading email or surfing the Web for people who wouldn’t know Unix from unicorns. However, since I chose the dynamic IP addresses of an ISP well-known for attracting hackers, this particular set of IP addresses is -- interesting. Check out “198.987.999.036 80 139”, “198.987.999.050 80 139”, and “198.987.999.156 80”. Those 80s represent ephemeral Web sites, in existence only so long as their dialups last. Wonder what they hold? The fact that almost all other services are turned off suggests sophisticated users. Maybe those Web sites will be passworded, or maybe I can get in... That “198.987.999.033 7 9 11 13 15 19 21 23 25 37 53 79 80 110 111 113 139 143” must be a Linux or other home Unix type box. It’s run by a real novice, I’d say, judging from all those open ports. Look at that port 21 open. Wonder if he or she has an anonymous ftp server? Better check it out before it winks out of existence. It also has a Web server... Take a look at “198.987.999.051 21 22 23 25 37 70 79 109 110 111 113 143”. That port 22 -- that means secure shell login. No webserver (80), no echo (7), discard (8), daytime (13), netstat (15) etc. Since these are ports that a cautious sysadmin would disable, these are signs this the box might be owned by a hacker. If this is a dynamically assigned IP address from an ISP on which you have a shell account, a quick look at netstat and/or the “last” command will probably reveal the user name of this hacker. Check out “198.987.999.198 110 119 139” and “198.987.999.178 135 389”. Weird selection of ports. Wonder if the owners of those boxes would tell me what they are up to? Hey, there’s a POP server (110). Maybe if I email “root@198.987.999.198” I will get a message through. Sheesh, I don’t know, I’m just playing around. Hacking. It’s OK to make mistakes and hit dead ends, because real hackers mess around, explore, and try out new things. If things don’t work, it’s no big deal. If they do work, however... If you have a Unix type computer, there are many other port scanners available. SATAN (Security Analysis Tool for Auditing Networks) is famous, free, and also will often identify ports that are vulnerable to attack. You can get it at ftp://ftp.cs.ruu.nl:/pub/SECURITY/. Possession of the code for SATAN is enough to get you kicked off some ISPs. Check out http://www.rootshell.com for other Unix port scanner programs that may not get people as suspicious at you. If you are willing to pay lots of money for a port scanner, several computer security companies sell them. Internet Security Systems (ISS) has an exceptionally good one, Internet Scanner (at http://www.iss.net). Like SATAN, Internet Scanner will identify security holes in the ports you scan. There are versions for both Unix and Windows NT systems. Because their software would be dangerous in the wrong hands, ISS will only sell you a version to scan the IP addresses you own or that the company you work for has given you permission to scan. Stealth Port Scanning You may have already heard that there are port scanners that are impossible to detect. If true, that would solve the problem of getting kicked off your ISP for running scans. One that I have tried out is Nmap, available for free from http://dhp.com. It runs on Unix type operating systems, and has options to do both normal port scanning and “stealth” port scanning. Warning -- like What’s Up, Nmap is not always accurate. While What’s Up misses open ports, Nmap often erroneously says closed ports are open. **************************** Wizard tip: Here’s why Nmap is inaccurate in fin scan (stealth or half-open) mode. It sends to each port on the victim computer a single packet with the fin flag (end of transmission) set. If it gets back a packet with the rst (reset) flag set, it reports the port as closed. If it doesn't get rst back, it reports it as open. Of course a dropped packet can also account for the missing rst. As a result, on a noisy connection Nmap shows many ports as open that aren't. Try fin scanning a nonexistent host with Nmap and you will see all ports reported open. On a theoretical basis, any scanner that sends only a single packet to probe each port is vulnerable to false results. *************************** There is another problem that afflicts all stealth scanners. They actually can be detected, and the sender identified, if the target network is running the right sniffer software. EtherPeek (discussed in detail below) is one we have tested against Nmap on the Happy Hacker Wargame (see http://www.happyhacker.org for details on how to play our Wargame). We discovered that EtherPeek definitely detects and identifies the user of stealth port scanners. How to Tell What Ports are Open on your own Computer It’s a good idea to regularly check what ports are open on your own computer. If you discover a new port -- time to investigate. For example, an open port 31337 is an almost sure sign that your computer has been taken over by the Windows Back Orifice Trojan. (See the “How to Break into Windows 95/98 Computers” chapter for removal instructions.) It is possible to check all your ports with just the tools that are already part of your Windows or Unix operating system. The “netstat -a” command will show all the ports open on your computer. Here’s what I get on a home Linux box: ~ > netstat -a Active Internet connections (including servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 134 fu.ml.org:telnet pma03.foo66.com:1030 ESTABLISHED tcp 0 0 *:www *:* LISTEN tcp 0 0 fu.ml.org:22 *:* LISTEN tcp 0 0 *:smtp *:* LISTEN tcp 0 0 *:2049 *:* LISTEN tcp 0 0 *:660 *:* LISTEN tcp 0 0 *:printer *:* LISTEN tcp 0 0 *:auth *:* LISTEN tcp 0 0 *:finger *:* LISTEN tcp 0 0 *:imap2 *:* LISTEN tcp 0 0 *:pop3 *:* LISTEN tcp 0 0 *:login *:* LISTEN tcp 0 0 *:shell *:* LISTEN tcp 0 0 *:telnet *:* LISTEN tcp 0 0 *:ftp *:* LISTEN tcp 0 0 *:time *:* LISTEN tcp 0 0 *:sunrpc *:* LISTEN udp 0 0 *:2049 *:* udp 0 0 *:657 *:* udp 0 0 *:ntalk *:* udp 0 0 *:biff *:* udp 0 0 *:time *:* udp 0 0 *:syslog *:* udp 0 0 *:sunrpc *:* raw 0 0 *:1 *:* Active UNIX domain sockets (including servers) Proto RefCnt Flags Type State I-Node Path unix 2 [ ] STREAM 3870 /dev/log unix 2 [ ] STREAM CONNECTED 3869 unix 2 [ ] STREAM 475 /dev/log unix 2 [ ] STREAM CONNECTED 474 unix 2 [ ] STREAM 434 /dev/log unix 2 [ ] STREAM CONNECTED 433 unix 2 [ ] STREAM 281 /dev/log unix 2 [ ] STREAM CONNECTED 280 unix 2 [ ] STREAM 257 /dev/log unix 2 [ ] STREAM CONNECTED 252 unix 1 [ ACC ] STREAM LISTENING 247 /dev/printer unix 2 [ ] STREAM 246 /dev/log unix 1 [ ACC ] STREAM LISTENING 207 /dev/log unix 2 [ ] STREAM CONNECTED 198 How about seeing what ports are open on your Windows computer? If you are not on a LAN, chances are there won’t be much to see. Here’s what my stand alone Win98 computer (her name is Lovely_Lady) says when I am on America Online: C:\WINDOWS>netstat -a Active Connections Proto Local Address Foreign Address State TCP lovely-lady:137 LOVELY_LADY:0 LISTENING TCP lovely-lady:138 LOVELY_LADY:0 LISTENING TCP lovely-lady:nbsession LOVELY_LADY:0 LISTENING UDP lovely-lady:nbname *:* UDP lovely-lady:nbdatagram *:* How to Give Computer Criminals a Hard Time Now -- are you ready for war? First, you need to know whether an intruder is on your system. How to do that is worth at least another entire chapter that I haven’t written yet. However, there are some hints for sysadmins I can give you on the basis of first hand experience from our Happy Hacker Wargame. Don’t expect this to be more than a tiny bit of all you should be doing to detect intruders, however. · Look for unusual traffic patterns -- for example, many ftp sessions, or a user who hasn’t logged into a shell account for months suddenly spending hours at a time logged in. · A new user name and account that no one remembers creating · Watch the processes. A skilled hacker may replace the “ps” command with a Trojan that hides his or her activities. However, you might see a high CPU utilization when the processes running couldn’t account for it. Time to go red alert! · Check whether system configurations have changed, for example new ports open. Or if your policy is to automatically kill all processes when a user logs off (most ISPs do this), perhaps you will discover processes left running after logoff. · Look for an Ethernet card on your local area network that is in promiscuous mode (meaning it is accepting all packets broadcast on the network). That probably means an intruder is sniffing your network with a program hidden on the computer with the promiscuous mode card. · Look for suspiciously large files turning up. They may be secret sniffer logs. · Do you notice a hacked Web page or obscene Message of the Day -- OK, this suggestion is lame, you knew those signs of hacker attack already! Of course it’s far better to detect your attacker before he gets inside. Signs that someone is trying to break in are basically activities that we all like to do such as port scans and telnet connections to unusual ports. Coming up in Part II: both free and commercial programs that help you fight intruders! # # # Guess what? “The Happy Hacker Book” has almost sold out its First Edition, published March 31, 1998. So American Eagle Publications is putting out a Second Edition, due to come off the presses Sept. 31, 1998. It has several all-new chapters as well as updates to cover Windows 98 and the major changes that are happening in email forging and spam fighting. How’s that -- only six months between editions? This is partly because people were so quick to buy out the First Edition -- and partly because the hacking scene is changing so fast. So instead of going to a second printing, the publisher agreed to spend the extra money to create a Second Edition so we could keep you as up to date as possible. If you want to buy one of the few remaining copies of the First Edition of “The Happy Hacker” (soon to be a collector’s item), you can order it from me ($34.95 for Priority mail shipping in the US; $35.95 airmail in Canada and Mexico; email me for quotes outside the US) by sending a check or money order to PO Box 1520, Cedar Crest NM 87008. Since I only have 18 copies left today, if your order comes in too late, be sure to tell me whether I should just return your money or if you want me to hold on to it and be among the first to get a Second Edition. Oh, yes, I autograph all books bought directly from me. _______________________________________________________________________ Where are those back issues of GTMHHs and Happy Hacker Digests? Check out the official Happy Hacker Web page at http://www.happyhacker.org. We are against computer crime. We support good, old-fashioned hacking of the kind that led to the creation of the Internet and a new era of freedom of information. So don’t email us about any crimes you have committed! And don’t expect us to come to your rescue if you crash 100 million computers with some new Java virus you just unleashed. To subscribe to Happy Hacker and receive the Guides to (mostly) Harmless Hacking, please email hacker@techbroker.com with message "subscribe happy-hacker" in the body of your message. Copyright 1998 Carolyn Meinel. You may forward, print out or post this GUIDE TO (mostly) HARMLESS HACKING on your Web site as long as you leave this notice at the end. _______________________________________________________________________ Carolyn Meinel M/B Research -- The Technology Brokers http://techbroker.com