totse.com | Packet Attacks v2

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Let me start by saying the internet is full of wonderful tools and papers like this one. A lot of these things can help you increase your knowledge, perhaps your job or more. But just as easily as you can learn from them, people read into them to much and decide to harm other peoples work for no apparent reason. Let it be known that is in no way the purpose of this paper. A true hacker is one who strives to attain the answers for themselves through curiosity. Its the path we take to those answers that makes us hackers, not destruction of other peoples work. So with that said, please enjoy my work, as I have enjoyed writing it.

The flow of data has always captured my interest. Just how does it work, how can we dissect it and use it to our advantage. Well I have spent a long time studying all of this, and that is why I wrote this paper. It's a collection of run on sentences on different packet attacks and how they work. Now we all know you can learn all you ever wanted to know about the specifications of a protocol by reading its 30 page RFC document.

But that is the protocol according to design, in the wild its a different story all together. 'Packet Attacks' covers everything from basic DOS attacks to TCP/IP hijacking. Hence the name "Packet Attacks". This paper also focuses not just on attacks but practical ways to prevent such attacks and ideas on new methods to help us stop them and secure our networks.

Introduction

Well I assume most of you reading this paper already have a good understanding of TCP/IP and how it works so I wont get to much into detail on that, but I will scrape the surface on the parts we NEED to discuss. The internet is a MASSIVE web of machines all connected to one another through a series of hardware devices known as routers, switches, hubs, bridges and lots more. All of these devices (although some are smarter then others) push along packets. Our operating systems and applications craft these packets in order to send data to one another over the wire. Each packet, although varying in size, carries a small bit of data to and from one host to another. Each packet must also carry its own personal information such as where it came from and where its headed. Of course there is a lot more to a packet then just this information. But as far as attacks go this is the crucial information we need to look at. Now there are many many different types of protocols that craft many different types of packets. And they are all read differently when they are received at the other end. Where as an ARP packet may tell a host who has this MAC address on this subnet, a TCP packet might transfer the last few bits in that MP3 your downloading. Regardless the data, all of these packets use the same wire to move to and from locations. I couldn't possibly discuss every protocol and packet structure in this one paper. The average end user takes for granted all of this running in the background while they surf the net. Most people don't understand the complexity of this internet we are all so familiar with, the chat rooms etc. But there are people who do, and there are people who take advantage of that. Reverse engineering has led to the creation of attacks using the basic fundamentals these protocols rely on. And since TCP/IP is so embedded in our infrastructure we must adapt and learn to defend each new attack.

OSI MODEL

Open Systems Interconnection model, is a seven layered networking design. Its an industry standard that defines exactly how data is transffered between protocol to protocol. Not every protocol follows the OSI model exactly and some do. TCP the internets main mode of data transport does not follow it exactly. Let me take you through a brief over view of the OSI model.

Layer Seven : Application Layer

This layer is obviously application specific, it provides everything from authentication to email to ftp and telnet, the list goes on. Its specifically for end user processes, what we input into our applications we can see on our screens.

Layer Six : Presentation Layer

This layer changes and possibly encrypts the data so that the application layer can understand it. (you will understand what this means in a few minutes)

Layer Five : Session Layer

Think of this layer as Establishment, Control and Termination of the sessions formed by the application(client) to a remote host(server).

Layer Four : Transport Layer

This layer is responsible for the invisible transfer of data between host to host. It is there to ensure all data transfer goes accordingly. The protocols used are, UDP and TCP.

Layer Three : Network Layer

This layer is for error correction, packet sequencing, and for transmitting data from node to node. Addressing is also another function of this layer in inter-networking.

Layer Two : Data Link Layer

This layer decodes and encodes packets into bits so they are ready for the physical layer. It also handles error correction in the physical layer. This layer is also divided into two different sub-layers. The LLC (logical link control) and MAC (media access control) sub layers. The LLC sub layer provides control for frame synchronization and error checking. The MAC sub layer controls how a computer on your network has access to data.

Layer One : Physical Layer

This layer is the actual movement of the data. Using electrical impulse or some other form of data movement is pushes the bit stream towards the other host. This layer is the hardware level, the ethernet card, the wire etc. There are many protocols within this layer.

You may ask yourself why I listed these from 7 to 1. Well I did to show you how the OSI model really works. Layer Seven really comes first, the end user types something into his instant messenger (for example) and the data flows down through the OSI model being encapsulated and changed at every level it has to be changed or corrected at. The data travels the wire and at the other end it moves back up the OSI model all the way back up to layer seven where the other host can read it in the original form it was sent. So there's a VERY basic understanding of the OSI model and how it works to transmit data from host to host. There is alot more protocols and parts to the OSI model but this basic representation should provide a firm understanding.

To understand all of this more in depth please get your hands on a few RFC (request for comment) documents and start reading. Because it will take you a very long time to understand exactly how TCP/IP works. If your very knowledgeable in the way TCP/IP works then this paper should make a lot of sense to you, perhaps even bore you! :( On the other hand if you don't understand TCP/IP as well as you would like to, you still might get something out of this. I try and explain all of the technical writing as easily as I can. Feel free to email me if you have a question or comment. Thanks :)

Chapter 1

The most common attack on the internet today is a denial of service attack. There are many programs on the internet today that will assist anyone in crafting one of these attacks. The sad part is for as easy as they are to make their power can be destructive when used properly. No matter what kind of packet attack it may be most are based on the same principal, volume. Thousand and thousands of spoofed packets will eat up network resources within minutes, choking and essentially 'killing' any network. There are many types of packet attacks. Some are more sophisticated then others. I will also talk about TCP/IP hijacking and your typical port and vulnerability scans among other things.

Why do people launch these attacks? How are they launched? How do they exactly (technically speaking) 'choke a network'?! Hold tight im getting to that. The lower end of these attacks are usually launched by what the hacker community calls a script kiddie. You see a hacker isn't a mindless web defacing juvenile (please see the mentors manifesto). A hacker is a person of true intellect and would never craft such an attack for no reason. But these lower end attacks are usually launched at peoples individual machines. Their IP address's may come from an IRC chat room, yahoo messenger, AOL, ICQ, or whatever other messenger you might use. Although not as sophisticated, these 'lower end' attacks can still knock an individual machine offline in minutes. The slightly more advanced attacks may be aimed at a business competitor in order to slow their sales or disrupt their outgoing internet connection. Whatever the reason may be they are usually launched for a reason. Attacking a box for no reason is typically useless and will only take up your own bandwidth.

The more sophisticated attacks are aimed at government and root points of the internet. Such as the attacks on the root DNS servers in October of 2002. These attacks were sophisticated in the way they were crafted. The attacks lasted for over an hour and successfully took out a few of the servers. If the attack had lasted just a few more minutes who knows the damage it could have caused. The possibility of the authorities solving these attacks and apprehending the offenders is slim to none because they are created and launched by skilled malicious individuals. They were also distributed denial of service attacks. Which means the 'zombie' machines that attacked the servers were spread out all over the world. We will touch more on that later though.

You will learn more about how these individual attacks are crafted and how they work later in this paper but this is small introduction so you can get a vague idea. Creating spoofed packets requires an open socket. This socket binds to an IP and a port and allows you to inject a packet onto the wire or accept any incoming packets to that IP and port. *NIX openly supports open socket programming (many tutorials on this type of programming). Which means you can code programs that create packets and then inject them into the network with ease. An example of this would be a program called "SENDIP" which allows you to create custom packets, and it supports many protocols (another good program is nemesis). I have written a few tutorials using SENDIP, I think its a great program for both advanced and new network engineers to use. It will help you learn about packet structure and the different protocols it supports. Microsoft is not an open source company, which pretty much makes it even harder to find help in creating these sorts of programs for Windows. But it is possible to craft these attacks from within a Windows environment. Its referred to 'Winsock' programming. Infact most of these DDOS attacks are because of vulnerable Windows boxes out on the net. They are sitting ducks for trojan horses and other programs that craft these attacks on servers when commanded from a client program to do so. Most end users do not understand security and how easy it is to break into someone's home computer, so they lack firewalls and virus scanners. This leads to many zombie machines available to hackers disposal on the net. All one has to do is scan a class C subnet for open trojan ports and hack their way into those trojans and use them as a backdoor, another zombie is created for attacking remote targets. Almost every program that interacts with TCP/IP generates packets to and from places, this is valid traffic. As you read you will distinguish the difference between valid and non valid, as it easy pretty easy to understand what I am explaining when I say "attack". When creating an open socket and crafting spoofed packets these programs tell the kernel they are going to construct their own IP headers. Usually this information is put on by the kernel before exiting the machine. But in this instance we are telling the kernel we want to specify our own information. Not all operating systems will allow this. And no I don't have a detailed list of which do and which dont. Most of the experiments I have conducted on my network used different versions of RedHat Linux, Mandrake Linux, and Windows XP.

Chapter 2

There are several different types of packet attacks. There's the simple brute flood of ICMP packets which floods a network and eats up all the available bandwidth. And then there are more sophisticated attacks like the Smurf or SYN/ACK attack. All of these attacks target different things. While the SMURF attack may target the general network its attacking, the SYN/ACK attack targets a specific host or service running on a host. We also must take into consideration when a target is attacked it may not be the only machine affected. There are many routers and other boxes transferring the data between point A and point B. Other peoples legitimate data is flowing between them, and may be disrupted by the packet flood. Even a top of the line router can only handle so much data. And unfortunately it is very easy to attain source code for these attacks all over the web. Lets take a more detailed look at each attack.

ICMP Brute Flood Attack

ICMP works on top of TCP. The ICMP protocol is simple yet very effective. Its used for error correcting and testing network connectivity. Your average PING program uses ICMP packets to test network connectivity. By sending a small amount of arbitrary data in an ECHO_REQUEST packet it waits for a reply from the target host, simple right? A typical ICMP packet is called an ECHO_REQUEST. You send 4 or 5 of these at a target machine and when it arrives there it requests an ECHO_REPLY. Thats when everything is done according to design. If you want more info on an ICMP packet and how it works then read my tutorial on that!

In this attack the source IP address is spoofed. So now hundreds, thousands of ECHO_REQUEST packets rush towards their destination. They reach point B, request an ECHO_REPLY for every ECHO_REQUEST sent. Point B says OK, reads the source IP. The source IP ends up being unreachable. ut point B is waiting a small amount of time (milliseconds) to determine that for every packet thats hitting it. It will be a few more moments before the process relinquishes this small bit of memory back to the system. This adds up to a great deal of packets and memory allocation building up. Now if these packets are coming from multiple source zombies (DDOS) then this means there each coming from different routes. So even if one ISP stops one attack, there are still many more zombie machines attacking the victim. All of this is eating up time and bandwidth, because with every millisecond that passes more and more bandwidth is being taken up. Eventually point B can no longer keep up with the ECHO_REQUESTS and his connection is completely flooded and of no use. On an unprotected system or router this attack can be very consuming. This attack is also sometimes referred to a bandwidth attack. Even if the target is running an advanced firewall it cannot protect the wire it connected to from being flooded with packets. There have been changes in this attack as well. On the net there are what we call amplifiers. On every network there are the network and subnet addresses. In many default configurations when you ping either one of these addresses they multiply the echo requests by 4 or more. So a zombie would attack a vulnerable network (.0) or subnet address (.255) with a spoofed source IP, being the victims real IP. So even tho the traffic becomes valid as far as IP addresses go. The victim gets bombarded with massive ECHO_REPLY packets. You will see more of this description in other attacks, as it works for some of those to.

Hopefully that simple drawing shows you exactly how this attack works. Its very very simple, massive ICMP packets with spoofed address's taking up network resources. The simplest of attacks.

Smurf Attack

(first part is repeat from ICMP attack) There have been changes in the ICMP attack. On the net there are what we call amplifiers. On every network there are the network and subnet addresses. In many default configurations when you ping either one of these addresses they multiply the echo requests by 4 or more. So a zombie would attack a vulnerable network (.0) or subnet address (.255) with a spoofed source IP, being the victims real IP. So even tho the traffic becomes valid as far as IP addresses go. The victim gets bombarded with massive ECHO_REPLY packets. You will see more of this description in other attacks, as it works for those to. You can try this attack on your home network by simply opening a packet sniffer on each machine that is on. Pick a machine, any machine and ping your broadcast address. Mine is 192.168.0.255 Immediately you see each machine receiving a broadcast packet. Now imagine its several hundred and each one has a spoofed source IP address. Its a brute ICMP attack on a massive scale, this possibilities to this attack are endless. You could easily implement this attack in anyway you chose. You could spoof the victims real IP as your source IP and create massive volumes of legit ECHO_REPLY packets. Even though its valid traffic, its 4x or more times the normal load of valid traffic. This consumes the connection and valid traffic cant pass, or passes so slowly it makes no difference to the end user.

[zombie machine] --> ICMP ECHO_REQUEST source ip = 10.2.2.2 --> to: broadcast router 4.1.0.255 (router multiplies the ECHO_REPLY packets by 4x! --> --> --> --> [victim 10.2.2.2]

SYN/ACK Attack

The SYN/ACK attack is a very powerful attack. SYN/ACK packets are also used in TCP hijacking, and the TCP/IP three way handshake. When an application wants to connect with a server somewhere over the net via a TCP connection (connection vs connectionless data transfer (UDP)) it first sends a SYN packet. The SYN packet tells the target machine he wants to make a connection on a certain specified port, and then send data. When the target machine read the SYN packet it replies to the original host with a SYN packet of his own and an ACK (acknowledgement) packet with sequence and ack numbers. These SEQ and ACK numbers are used to synchronize the data transfer, incase one or two packets gets lost or slowed down along its route, it can be assembled again in the correct order. The orignal machine replies again with another SYN ACK packet combination acknowledging the sequencing numbers and then it starts to send data. When it creates this connection a tiny piece of memory is allocated to hold the connection while the packets are in route. Now a SYN/ACK attack would consist of spoofing the source IP address on the original SYN packet. The target receives the request for a connection, reads the spoofed source IP and tries to send its own SYN and ACK packet to a destination that does not exist. Most operating systems will continue to send SYN/ACK packets if they dont receive a reply as a method of error correction and guaranteed data delivery. Just like in the ICMP attack the machine has to wait a few milliseconds before abandoning all hope of reaching the machine. So these tiny allocated spaces of memory are building up with every spoofed packet that arrives at the target. This attack is very powerful and can disable a service running on the target machine in a matter of minutes. Not to mention all the available bandwidth is eaten with thousands and thousands of spoofed packets. So there is the SYN/ACK attack in a brief description.

[zombie machine] --> SYN packet (source IP 1.1.1.1, port = 23 telnet) (seq = 100) --> [target]

As you can see from the simple drawing above the target machine has no idea who is sending the SYN packets and the telnet server he is running on port 23 would most likely crash. At best the telnet daemon would not allow any other legitimate traffic through, as it could not gather enough resources (memory, bandwidth) to make the connection due to all the spoofed packets.

Another use of this attack is to disconnect a user from their current TCP session. By spoofing SYN/ACK packets to a server a client is currently using. An attacker would place a "FIN" flag in the packets, this tells the server the client is done sending data. Client uses his connection and attacker walks away undetected, because it only took one packet to accomplish this.

UDP Attack

UDP is a protocol that is used to transfer data. Short for USER DATAGRAM PROTOCOL. UDP offers very little error correction and is used as an alternative means for data transfer. It doesn't require the 3 way handshake such as the SYN/ACK method, so its initial attack may not take down a remote daemon as quickly. UDP is generally used to broadcast messages over a network. A UDP attack would consist of spoofing the source IP addresses and specifying a port number like in the SYN attack above. UDP packets are generally large because they are usually used on closed 100mb subnets (LANS). So an attack would set flags in the packets and fragment them (break them up and flag where in the packet they broke, so they can be reassembled on the receiving end). For example in Windows 2000 there was a remote UDP DOS exploit that used the IKE service running on port 500. All an attacker had to do was connect to port 500 on a random machine with that port open. Start sending massive UDP packets (above 500 bytes) to that service and the CPU usage would hit 99% and the machine would lock up. The typical ports that accept UDP packets are 7, 13, 19 and 37 on a Windows box.

DNS Attack

The DNS attack is a special one. Not as easily crafted as the others, there aren't that many tools readily available to the average script kiddie to construct such an attack. The DNS protocol is used for name resolution, 216.239.35.100 = google.com, simple as that? Well not really. A DNS attack is based on the fact that a DNS query takes very little data and bandwidth to create, but a DNS response is much bigger. So this is how a DNS attack would look like.

[dns query packet (who is google.com)] --> source IP is 10.10.10.10 --> [dns server]

[dns server] --> --> --> [dns response] [dns response] [dns response] --> [victim]

As you can see the attack is sort of relayed from a legitimate DNS server. Although the DNS response packets are 'legit' there is a massive flood of them because the DNS server that is sending them is a very good machine on a very good connection. The end user, most likely a home pc, gets flooded with these huge DNS response packets it never asked for.

ARP Attack

The arp attack is a special one, it can be used to 'hijack' a tcp connection currently in session or it can be used to sniff the legitimate traffic on a wire other then your own. Which is a very dangerous thing in the information world we live in today. There are a few methods of this attack. Lets say person1, attacker, and server are all on the same subnet. Person1 and server currently have an FTP session open. Attacker sends both server and person1 an ARP packet containing an invalid MAC address. Now both of their arp tables are messed up for atleast 30 seconds. Server and person1 cant find that invalid MAC address so they send their data to the IP its associated with, the attacker. So in this case the attacker has a sniffer setup and hes collecting a ton of data. Now the attacker (an advanced one at that) can issue commands as person1 to the server. This attack takes timing and skill to pull off on the internet, but on a LAN its very easy. It only allows for maybe 30 or so seconds of sniffing, until their arp table is constructed properly again.

DRDOS Attack

A DRDOS attack uses a little of other attacks to inflict damage. This attack spoofs the source IP address of SYN packets to the IP of the victim. It requires a third party. This is the part of the attack that makes it so easy. All it needs is some ftp, web server, telnet.. ANY service that will reply with an ACK packet, anywhere on the internet. Could be Angelfires free ftp servers, could be your neighbors web server running off his 233mhz Compaq with IIS 4.0. It doesn't matter! The SYN packets are sent to that services IP address and they of course reply with a steady stream of SYN/ACK packets to the victim. Most likely directed towards an open port on the victims machine, crashing that service and the system. These attacks are near impossible to track down. This attack is quite possibly the strongest DOS attack in my opinion. For every SYN packet you send the middle man, it sends out up to 4 SYN/ACK combinations to the victim. And each time the victim doesn't respond the middle man sends even more (error correction). This allows the attacker to construct a massive attack from just one machine with a broadband connection. There are more dangers to this attack as well, there are hundreds of thousands of FTP, web servers and many more services running on the net today that will deflect these SYN/ACK packets at the victim. So in theory this attack could use any number of 'middle man' servers to bombard your network with packets.

Bot / Trojan DrDOS Attack

Recently many IRC bots and trojan servers have found their way to users home computers via email and .exe binding etc. They are just backdoors to any system they have infected. If u really want to read into this goto www.grc.com This guy knows a lot about these attacks because he was the target of one. These bots infect a machine and join an irc server and a private channel. Its an army of zombies collecting in a room. The attacker enters the room and can issue commands at the army of bots to attack a target anywhere he wants. With any kind of attack he wants to use. This type of lameness can be easily stopped with a home firewall like zone alarm and denying internet access to the bot. Or a good virus scanner, both should come standard with every operating system. But you will have to email Bill Gates about that one. The attack its self is a bit like bandwidth hogging, the term is DrDoS (Distributed Reflected Denial of Service). Another analysis of the attack is below,

Not to go into much detail about this one, however it must be said, this attack type is full power and if used in the wrong hands could and most likely will cause serious damage, to the host attacked. Like above the attack all depends on the amount of zombies the hacker has, for example if a hacker had 30,000 infected zombies (bots) all with the upstream of 1024kbps, thats 30,000 meg upstream / a sec. Aimed at a web host for about 10 mins thats 300,000 meg a sec enough to take down some of the leading webhosts and even if the Ip's are blocked the router still has to say no to the packets, so by now you should see the problem. The fact is home users should be targeted to prevent these attacks at the source.

Once you open the bot/trojan it secretly logs you into a IRC room, where the hacker can sends group commands to all his bots. Keep protected with firewalls, such as "Sygate" www.sygate.com and anti-trojan system such as "The Cleaner" www.moosoft.com.

Worm Attack

Worms are special 'breed' of programming. There advanced, and very sophisticated. The recent SQL worm we saw came with a built in DOS attack on the servers it infected. The worm did not damage files or anything like that but it kept trying to find other servers to infect. It used big UDP packets in order to find other vulnerable servers to infect. When no servers that could be infected were, found the worm created DOS attacks on the networks it was on. The network became flooded with UDP packets, denying service to legitimate clients. A worm can also act like a Bot or trojan server. In which when it infects the target it instantly begins to attack a pre-programmed target with random source IP addresses. Its a deadly race to clean these worms, because the target may never be free of the attack if the worm infects enough people. This was the case with the Code Red worm. I suggest reading about the Code Red worm on the internet as it is very interesting :]

Unicode Ping Flood

This attack is native to the unicode bug found in most IIS web servers. Here's a sample:

http://imnotsecure.com/scripts/images/..%c0%af..%c0%af..%c0%afwinnt/
system32/cmd.exe?/c+ping+10.10.10.10-n+1000+-l

Ok this is one of MANY unicode strings that are possibly useful on a vulnerable server. But you see the unicode bug accessing the command shell on the target host. And then issuing the command to ping 10.10.10.10 forever with 1000 byte ICMP packets. Now these packets aren't spoofed but they are still traffic and with enough vulnerable machines the traffic volume begins to build up.

This section is very small, its on the topic of phasing. Phasing is a very simple yet very effective method of using DOS attacks without setting off alarms at a router somewhere for the volume of packets the attacker is sending. I will only give one example attack with this method since it is sort of self explanatory after you read it once. Lets take the DRDOS attack. Your sending spoofed SYN packets at servers all over the internet. Well without breaking a sweat you could code a program in C that simply switches the servers you are deflecting off of every 3-4 mins. It takes the server 3 or 4 mins to stop sending SYN/ACK packets when it doesn't receive any ACK in return from your victim. So after the 3 or 4 initial minutes of the attack you begin to phase your attack to a different server, and your packets take a different route. You could phase your attack over a group of 25 servers or a group of 1000 servers. Attacking with 5 at a time, and switching every 4 minutes. This method of attacking is very effective and doesn't raise any alarms. Which is not good.

TCP Hijacking

[zombie machine] --> SYN/ACK packets sent (seq = 101) (ack = 301)-DATA-DATA -->--> [target]

Above is the basic three way hand shake, according to design. Now there are different types of TCP hijacking. There are attacks where the attacker can actually issue commands, as the victim, to a server. This requires knowing the next sequence numbers the server is expecting from the client. This is difficult, but not impossible. And then there is passive sniffing of the traffic intended for the victim. In this method the valid traffic, after being sniffed and saved by the attacker, is all forwarded to the real client. This completely avoids any detection, the attackers machine just looks like another router. Now this is done by changing the victim or servers arp table. This attack is not limited to a subnet, it works on the internet to.

Lets say server1 has a connection going with client1. The attacker would ping his victim, client1. Capture the ICMP data and extract his MAC address from it. Now armed with that MAC address, the attack creates a spoofed arp packet and sends it to the server. The server receives the arp packet and changes its arp table. Now it thinks that client1's MAC address belongs to a new IP address, the IP address of the attacker. Now when the server constructs its packets to be sent to client1, it compares the MAC address in its packets to its arp table as it passes through the network layer of the OSI model. It matches up the MAC address with the IP address of the attacker. The traffic is then sent off directly to the attacker. Now to avoid detection, the attacker redirects the valid traffic, after logging it, to client1. Now the attackers machine looks like another router, almost unnoticeable to the average end user. This is called passive sniffing. This will only last until the server has updated its arp table. We can complicate this matter and change the clients arp table so it only sends its arp requets to the attacker first. Where he drops the packets, therefore server and client are never updating their arp tables, and the continous flow of data between them is logged by attacker.

Sniffing

There are different ways to 'sniff' the traffic of other machines. One was was described above using the arp method to redirect someone else's specific traffic at your own machine. This method only allows you to sniff the certain traffic you were looking for. But on a local subnet, say at your work or home, if you run a sniffer you can see ALL the traffic on the wire. This includes every protocol. This is called promiscuous sniffing. A packet sniffer works by capturing (copying) all the data on the wire. This traffic does reach its legitimate target, but you are viewing a copy of the raw packet in your packet sniffer. Packet sniffers usually dump the packet in the form of a HEX dump because it is easy to decipher and manipulate. Using a packet sniffer can be very useful, you can run your sniffer and ping a victim. This captures the return ICMP packet and an attacker can extract his victims MAC address from that data. A MAC address is very easy to pull from a hex dump because it is in HEX form to begin with. Some newer programs will even allow you to reassemble the packets and create what they were intended for. Now this is easier when reconstructing say HTTP packets then just a few TCP packets containing your MP3 data. The HTTP data is easier to reassemble. Another form of packet sniffing may be much more intrusive. An attacker can install a sniffer by remotely breaking into a machine. The attacker sets the sniffer to only pick up plain text login and passwords it finds in packets. Then he returns a few weeks later to retrieve the data the sniffer has found. This type of sniffing is the most dangerous because the attacker has full access to every single packet your machine generated and received since the sniffer was installed.

Scans

Scans are the most common thing on the internet. The average broadband customer receives up to 40 scans within the first three days of owning their new connection. There are 2 types of scans, port scans and vulnerability scans. A port scan is very basic but imperative to an attack for gathering information on your machine. A port scanner sends a SYN packet to each port specified by the attacker on the victims machine. If that port is open and there is a daemon / service running it returns a SYN/ACK packet and port scanner reports that port as 'open'. A firewall would pick up on the individual packet shape of the request for a certain port, and send no ACK back and possible connection Termination/Refusement. Certian port scanners like Nmap are extremely advanced and will have options to stealth scan, or not to ping the host. A vulnerability scanner scans an IP address for ports as well, but it goes beyond that. The vulnerability scanner attempts to scan the services running on the open ports for known vulnerabilities. Now most scanners are made for administrators to harden their security. But these tools are easily available to attackers. A typical vulnerability scanner will scan a website for known unicode bugs, buffer overflows, and weak passwords among many things. Now its not illegal to scan any IP address but its most likely the sign of an attack in the making. These types of vulnerability scans can also fill up a targets log files very quickly.

Information Gathering / Finger Printing

Before attempting to gather information on a remote target its important to build an information database on each of the possible OS the attackers target could be running. Such as identifier values, TTL, TOS, and possible services the OS could be running by default. Use this database to compare the results you build up after using various methods. Some of the simple "banner grabbing methods" work very well, but there are more stealth like methods, TCP/IP finger printing. Both methods are described.

Information gathering is an essential part to any attackers plan. But this cant always be done with neat little applications, it takes brains and skill if the attacker does not want to be caught. Before attempting to gain root access on a remote box an attacker must know what he's attacking. Different operating systems are like night and day, they all have different security holes and vulnerabilities. The attacker has probably already done a port scan on his target. Lets say for the sake of argument he has found port 21 (ftp) and port 80 (http) open. Well now he wants to know what version FTP and what web server his target is running. This is easy information gathering.

This will return an HTTP header and the type and version of the web server. If its IIS the attacker looks at the version # and can instantly tell what version WINNT or 2000 he is running. This method can be done on the FTPD port the target is running also.

Now the attacker just heads off to google.com to search for vulnerabilities in the software the victim is running. Its that simple, yes very lame and doesn't take much skill. But there is skill to information gathering. An attacker who didn't want to raise such attention to himself to the sites admin would use a different way of gathering this information. From one simple ICMP ECHO_REPLY a skillful attacker can read the values in the packet data to determine OS type. There are Identifier bits in packets. Here are a couple examples of identifier bits for Windows machines.

These above values are the values different Windows machines will return. *NIX machines return all different sorts of values as well, you will have to do more research on the value you get and match it up with your prepared OS information database.

The TTL value in a packet specifies how many hops the packet can travel before being dropped or recreated. The TTL value is another form of OS detection, a Windows box will return a TTL of 128. Where as a Redhat box will return a value of 64. Routers and switches will return a low value as well, usually around 64. These are little examples of TCP/IP stack fingerprinting. Its forensic work on a much smaller scale then running a vulnerability scanner on a target and alerting the admins that the attacker is inspecting them. Much can be told from examining one packet. The data inside the packet is irrelevant, the IP headers generated by the target are what you need to examine. Every OS has its own way of forming these headers and values.

Telnet is probably the best way of remote OS detection. If the attackers target has a telnet daemon running and he attempts to connect to it, he doesn't even need to logon with the proper credentials to see what OS and version you are running. For example

This is probably the most obvious form of remote OS detection. Its among the basic "banner grabbing" methods.

Finally I just want to suggest a tool on this topic, NMAP. NMAP can perform remote OS detection through various TCP/IP stack finger printing methods. There are command line and GUI versions, its very reliable and dependable. NMAP is just the first in a long line of tools available to you on the internet. But most of use the same methods described above, TCP/IP stack fingerprinting. Some OS can produce the same results as another OS and this can make it even harder to make an accurate guess at the OS. But this will eventually lead to better ways of detection.

Protecting yourself against the packet attacks described a few paragraphs above can be simple or can be hard depending on how you want to go about it. You must take into consideration your network topology as well, the way it is physically and logically setup. If you are running a webserver on port 80 then this port will be a sitting duck for SYN attacks. Unfortunately TCP/IP wasn't designed to be secure. This port needs to be open in order to accept legitimate SYN/ACK and HTTP packets among many. But you can still protect your network by installing basic firewalls. Firewalls are software or hardware that can be configured to allow and block certain specified network traffic. Firewalls are imperative for networks with machines behind them on a LAN. As well as for stand alone machines. Configuring your firewall is easy, first you need to examine the traffic you must allow in order for people to access your website or FTP server. At this point you may want to block the rest of the traffic. This isn't always a smart move. Outbound firewalls are usually only applied in a business environment when you want to restrict access to certain websites outside of the LAN. If every machine on your LAN is trusted, or its your home network then applying outbound firewalls may not be a good idea. It all depends on your situation. Outbound application blocking is however important in a home environment. A free firewall like Zone Alarm provides an excellent application blocking feature. You supply the firewall with a list of applications that can access the network, this blocks trojans and worms from spreading or making communication with the attacker over the internet. Inbound firewalls on the other hand must be hardened to secure your internal machines. Blocking all ICMP traffic would stop your attacker from receiving an ECHO_REPLY packet when he pings your IP address. But ICMP is sometimes very useful for error correction and network connectivity testing.

Your firewall can also be configured to detect a flood of traffic. Lets say your web server isnt hosting any applications for download. Its a simple web page designed to update your viewers on current news and things happening in your business. Well this means there wouldn't be that much traffic flowing between you and your viewers besides the normal HTTP packets. You can configure your firewall to stop responding to a certain IP address after your server receives 'X' amount of packets from them in 'Y' amount of time.

Above we talked about the Smurf attack. The attacker uses your router in order to broadcast these massive amounts of packets throughout your subnet. By default these routers are set to broadcast this traffic that hits their network address of .255 . This can be as simple as disabling that feature! Yes my friends these precautions seems almost ridiculous. You must be thinking anyone that doesn't do this the second they set their machines up is truly dense. But these attacks happen everyday, all over the internet. Default installs will be the death of the internet.

Many of the DOS attacks above have no perfect solution to stopping them. Its a game of wits, out smarting your attacker is the best way to stop these attacks from happening. Keeping your software up to date and your hardware configured correctly is the best way to secure your network. Often running vulnerability scans and attempting to exploit and break your own network is the best way to protect it from malicious attackers.

Attack Detection

Detecting attacks on your network are quite easy. In the event of a DDOS attack you will most likely notice your internet connection is dead. The only traffic that moves fast is the traffic inside of your network, depending on the attack. Then there are the physical signs, your switches or routers are all lighting up like a Christmas tree. Your firewall logs are the best place to go when you think you are the target of an attack. Here's a line from my routers firewall with the original IP address changed to hide the real attackers IP address.

Friday, February 21, 2003 5:32:38 PM
Unrecognized access from 10.10.10.10:38461 to TCP port 21

Friday, February 21, 2003 5:32:38 PM
Unrecognized access from 10.10.10.10:38461 to TCP port 23

Friday, February 21, 2003 5:32:38 PM
Unrecognized access from 10.10.10.10:38461 to TCP port 80

Friday, February 21, 2003 5:32:38 PM
Unrecognized access from 10.10.10.10:38461 to TCP port 443

This is an example of someone port scanning me for open ports. This type of stuff is easy to pick out of your logs because of how neat and clean it is. Its obviously someone sending one SYN packet to each port he wants to check on your machine. These logged attempts are usually right next to one another. Now a SYN attack would most likely look similar to these logs. Except they would all be directed towards the same port and the source IP would look obviously fake such as this 1.1.1.1

Friday, February 21, 2003 5:32:38 PM
Unrecognized access from 1.1.1.1:38461 to TCP port 80

This would most likely be a SYN flood trying to kill my web server. To stop this attack you can configure your firewall to stop receiving packets from 1.1.1.1, The attacker may just choose another source address when he realizes what you've done, but this gives you enough time to prepare yourself.

Another way of detecting these attacks is to run a packet sniffer. Download ethereal packet sniffer from www.ethereal.com and set the filters to only pick up ICMP traffic. Ethereal doesn't have a huge buffer to hold the captured data so when it begins to grow large, thousands of ICMP packets. Its time to stop the capturing and examine the packets. These logs are useful to save in order to show the authorities or your ISP, in order to track down the attacker. A normal ping program produces an ICMP packet every few seconds. An ICMP attack will usually flood your wire with over 5000 packets in just under 10 seconds.

Intrusion Detection

Intrusion detection is easy as well, as will almost always help you catch your attacker if you are smart enough about it. On a normal linux box the most important logs are kept at /var/log and var/log/httpd by default. The logs you should look at are 'messages', 'secure', and 'access_log' in the HTTPD folder. These will accurately log who used what service on your machine. Usually an attacker will delete this logs upon leaving your machine. Thats why you should create backups and alternative places to log these files. Make it harder for the attacker to find these files, in hopes he will give up and you will have logged his real IP address. Lets take a look at one of these logs from my machine.

The 10.10.10.10 being the attackers IP address. This tells me exactly when he logged on my telnet daemon. By default my RedHat 7.3 machine is set to email my ROOT account whenever my FTP or Telnet daemon is accessed. These mails are kept in /var/mail. Lets take a look (deleting the email headers, they are irrelevant).

This mail also logs unsuccessful attempts at breaking your passwords. If a brute force program is used to break in your log file may become to large to read. So it is imperative you read these logs daily and sift through them for possible attacks.

IPSEC

IPSEC is a protocol that encrypts packet headers and data. IPSEC works by exchanging packets on the IP layer. It supports two types of encryption, tunnel and transport. The tunnel mode encrypts both the data and the IP header. Where as the transport mode only encrypts the data of the packet. IPSEC was designed to implement VPN's. The sender and receiver of the packets both share a public key to decrypt the packets. IPSEC ensures the validity of your data, and that even if sniffed, it is worthless to the attacker. For more on IPSEC please visit this page http://www.netbsd.org/Documentation/network/ipsec/

This next part is copied from my tutorial on NAT. I think NAT plays a substantial part in our networks security and I have decided to add my other work on NAT to this paper.

Now lets pretend the 100.10.2.3 address is a valid internet address on the backbone of the network. The three users are using 3 DHCP assigned addresses. They would not be valid IP's on the internet. But their packets go through the NAT router where their packet headers are stripped and replaced with the 100.10.2.3 valid IP header. This is a vague description of how this works. But it should give you grasp on what NAT is. Why NAT is good for security. What is easier to defend? One point of entry? Or a thousand points of entry? Of course one. NAT allows hundreds of machines to access the internet via one address. At this one address it is much easier to construct a firewall and keep out intruders from seeing your internal network. At this one access point we can setup different protocols allowing our outside employees to reach the internal network with the proper authentication. This doesn't have to be done on each internal machine because there is only one entry point instead of thousands. How do exiting packets return to their source? Easy, the NAT router does not strip the MAC address from the packets. So when user1 sends an ICMP echo request to lets say yahoo.com. NAT strips the 200.200.200.1 IP address but does not strip the MAC (media access control) hex number from the packet. So when the packet is returned the NAT router can check its ARP (address resolution protocol) table and send the packet to the right internal machine.

This brings us to the web security of NAT. Most webpages uses dynamic databases now using java or CGI script. They must be connected to some sort of database within the internal network where the average websurfer can't reach. But how are his packets supposed to reach that data? NAT takes the incoming packets and reads their destination port. Once the packet is inside the firewall NAT uses port forwarding and forwards the packet to the specific internal machine containing the database. As the packet exits the firewall on its way back to the user it is rewritten again to look like the firewall sent it. So you can see how NAT can help secure your webserver.

NAT can also provide load balancing for webservers. Lets say you have a very busy webserver. You get hits from all over the country every few seconds. These packets are beginning to slow down the time in which your server can respond. Well using NAT we can forward certain packets to mirror servers, thus making the load on the main server substantially smaller. NAT can separate these packets by shortest amount of hops they have to travel to return to their source and forward them to the appropriate mirror site. These mirror sites can be physically located throughout the country. All of this is done in seconds, the user never notices the new route their packet took.

So there is how NAT can play a very important role in your networks security. However NAT is just one of many protocols that can offer more security, NAT is however used in all operating systems and networks.

The Future of TCP/IP

This chapter could be 50 pages long or it could be one paragraph, but we will keep it short. TCP/IP was not designed to be a very secure means of transporting data. It is easily manipulated and exploited for every attackers advantage. Pherhaps IPv6 will bring more secure protocols with advanced methods of transporting data and routing. In the past people have suggested large centers in which data should be stored, encrypted, and then sent back out again. But this is against the internets original design, this creates a central point. This just opens doors to all new types of attacks and loss of data. If an attacker were to breach the security of these 'data' centers, the damages would be catastrophic. It is certain by this point that IPv6 will co-exist with IPv4 for a time. IPv6 will allow many more hosts to join the internet, and hopefully a great deal of new secure protocols for us to use and study.

Lets take for example the TCP protocol. Its imperative for the internet to transfer data. Yet its so easily manipulated. Now the average end user usually does not have the knowledge to manipulate it and cause damage. This is what has kept the internet to stable (I believe) over the past 30 years of its brief history. However these days we see more and more crackers releasing programs that craft these attacks so easily for the average end user.

Insert Victim, Click Here

Wow that took an enormous amount of skill? ...Right. So you can see how easy it is for script kiddies to launch these attacks with the current set of tools manipulating IPv4 protocols.

I would like to suggest a link on IPv6, http://www.ipv6.org/specs.html it is full of information and changes in IPv6.

Well that's it for my paper 'Packet Attacks'. Whether your getting ready to email me with a flame or question, I sincerely hoped you enjoyed this paper, as I have enjoyed writing it. Look forward to many more projects and papers by me. Thanks again for reading.

Packet Attacks v2

by Dreifachx and Data_Clast