WEB SPOOFING full report

Seminar Report’03 IP & WEB SPOOFING

1.0 INTRODUCTION

This paper describes an Internet security attack that could endanger the

privacy of World Wide Web users and the integrity of their data. The attack can

be carried out on today's systems, endangering users of the most common Web

browsers, including Netscape Navigator and Microsoft Internet Explorer.

1.1 HISTORY

The concept of IP spoofing was initially discussed in academic circles in

the 1980's. It was primarily theoretical until Robert Morris, whose son wrote the

first Internet Worm, discovered a security weakness in the TCP protocol known

as sequence prediction. Another infamous attack, Kevin Mitnick's Christmas day,

crack of Tsutomu Shimomura's machine, employed the IP spoofing and TCP

sequence prediction techniques. While the popularity of such cracks has

decreased due to the demise of the services they exploited, spoofing can still be

used and needs to be addressed by all security administrators.

1.2 WHAT IS SPOOFING?

Spoofing means pretending to be something you are not. In Internet

terms it means pretending to be a different Internet address from the one you

really have in order to gain something. That might be information like credit

card numbers, passwords, personal information or the ability to carry out actions

using someone else’s identity.

IP spoofing attack involves forging one's source address. It is the act of

using one machine to impersonate another. Most of the applications and tools in

web rely on the source IP address authentication. Many developers have used the

Dept. of CSE MESCE, Kuttippuram1


host based access controls to secure their networks. Source IP address is a unique

identifier but not a reliable one. It can easily be spoofed.

Web spoofing allows an attacker to create a "shadow copy" of the entire

World Wide Web. Accesses to the shadow Web are funneled through the

attacker's machine, allowing the attacker to monitor the all of the victim's

activities including any passwords or account numbers the victim enters. The

attacker can also cause false or misleading data to be sent to Web servers in the

victim's name, or to the victim in the name of any Web server. In short, the

attacker observes and controls everything the victim does on the Web.

The various types of spoofing techniques that we discuss include TCP

Flooding, DNS Server Spoofing Attempts, web site names, email ids and link

redirection.



2.0 WEB SPOOFING

2.1 INTRODUCTION








2.2 SPOOFING ATTACKS

In a spoofing attack, the attacker creates misleading context in order to

trick the victim into making an inappropriate security-relevant decision. A

spoofing attack is like a con game: the attacker sets up a false but convincing

world around the victim. The victim does something that would be appropriate if

the false world were real. Unfortunately, activities that seem reasonable in the

false world may have disastrous effects in the real world.

Spoofing attacks are possible in the physical world as well as the

electronic one. For example, there have been several incidents in which criminals

set up bogus automated-teller machines, typically in the public areas of shopping

malls. The machines would accept ATM cards and ask the person to enter their

PIN code. Once the machine had the victim's PIN, it could either eat the card or

"malfunction" and return the card. In either case, the criminals had enough

information to copy the victim's card and use the duplicate. In these attacks,



people were fooled by the context they saw: the location of the machines, their

size and weight, the way they were decorated, and the appearance of their

electronic displays.

People using computer systems often make security-relevant decisions

based on contextual cues they see. For example, one might decide to type in your

bank account number because he/she believes you are visiting your bank's Web

page. This belief might arise because the page has a familiar look, because the

bank's URL appears in the browser's location line, or for some other reason.

To appreciate the range and severity of possible spoofing attacks, we must

look more deeply into two parts of the definition of spoofing: security-relevant

decisions and context.

2.2.1 Security-relevant Decisions

By "security-relevant decision," we mean any decision a person makes

that might lead to undesirable results such as a breach of privacy or unauthorized

tampering with data. Deciding to divulge sensitive information, for example by

typing in a password or account number, is one example of a security-relevant

decision. Choosing to accept a downloaded document is a security-relevant

decision, since in many cases a downloaded document is capable of containing

malicious elements that harm the person receiving the document.

Even the decision to accept the accuracy of information displayed by

one’s computer can be security-relevant. For example, if one decide to buy a

stock based on information one get from an online stock ticker, he/she is trusting

that the information provided by the ticker is correct. If somebody could present

some incorrect stock prices, they might cause the victim to engage in a

transaction that the person would not have otherwise made.



2.2.2 Context

A browser presents many types of context that users might rely on to

make decisions. The text and pictures on a Web page might give some

impression about where the page came from; for example, the presence of a

corporate logo implies that the page originated at a certain corporation.

The names of objects can convey context. People often deduce what is in

a file by its name. Is manual.doc the text of a user manual? (It might be another

kind of document, or it might not be a document at all.) URLs are another

example. Is MICR0S0FT.COM the address of a large software company? (For a

while that address pointed to someone else entirely. By the way, the round

symbols in MICR0S0FT here are the number zero, not the letter O.).

People often get context from the timing of events. If two things happen at

the same time, you naturally think they are related. If you click over to your

bank's page and a username/password dialog box appears, you naturally assume

that you should type the name and password that you use for the bank. If you

click on a link and a document immediately starts downloading, you assume that

the document came from the site whose link you clicked on. Either assumption

could be wrong.

If you only see one browser window when an event occurs, you might not

realize that the event was caused by another window hiding behind the visible

one.

Modern user-interface designers spend their time trying to devise

contextual cues that will guide people to behave appropriately, even if they do

not explicitly notice the cues. While this is usually beneficial, it can become

dangerous when people are accustomed to relying on context that is not always

correct.



2.3 WEB SPOOFING

Web spoofing is a kind of electronic con game in which the attacker

creates a convincing but false copy of the entire World Wide Web. The false Web

looks just like the real one: it has all the same pages and links. However, the

attacker controls the false Web, so that all network traffic between the victim's

browser and the Web goes through the attacker.

Consequences Since the attacker can observe or modify any data going from the

victim to Web servers, as well as controlling all return traffic from Web servers

to the victim, the attacker has many possibilities. These include surveillance and

tampering.

Surveillance The attacker can passively watch the traffic, recording which pages

the victim visits and the contents of those pages. When the victim fills out a

form, the entered data is transmitted to a Web server, so the attacker can record

that too, along with the response sent back by the server. Since most on-line

commerce is done via forms, this means the attacker can observe any account

numbers or passwords the victim enters.

The attacker can carry out surveillance even if the victim has a "secure"

connection (usually via Secure Sockets Layer) to the server, that is, even if the

victim's browser shows the secure-connection icon (usually an image of a lock or

a key).

Tampering The attacker is also free to modify any of the data traveling in either

direction between the victim and the Web. The attacker can modify form data

submitted by the victim. For example, if the victim is ordering a product on-line,

the attacker can change the product number, the quantity, or the ship-to address.



The attacker can also modify the data returned by a Web server, for

example by inserting misleading or offensive material in order to trick the victim

or to cause antagonism between the victim and the server.

2.3.1 Spoofing the Whole Web

You may think it is difficult for the attacker to spoof the entire World

Wide Web, but it is not. The attacker need not store the entire contents of the

Web. The whole Web is available on-line; the attacker's server can just fetch a

page from the real Web when it needs to provide a copy of the page on the false

Web.

2.3.2 How the Attack Works

The key to this attack is for the attacker's Web server to sit between the

victim and the rest of the Web. This kind of arrangement is called a "man in the

middle attack" in the security literature.

2.3.3 URL Rewriting

The attacker's first trick is to rewrite all of the URLs on some Web page

so that they point to the attacker's server rather than to some real server.

Assuming the attacker's server is on the machine www.attacker.org, the attacker

rewrites a URL by adding http://www.attacker.org to the front of the URL. For

example, http://home.netscape.com becomes

http://www.attacker.org/http://home.netscape.com.

The victim's browser requests the page from www.attacker.org, since the

URL starts with http://www.attacker.org. The remainder of the URL tells the

attacker's server where on the Web to go to get the real document.



Once the attacker's server has fetched the real document needed to satisfy

the request, the attacker rewrites all of the URLs in the document into the same

special form by splicing http://www.attacker.org/ onto the front. Then the

attacker's server provides the rewritten page to the victim's browser.

Since all of the URLs in the rewritten page now point to

www.attacker.org, if the victim follows a link on the new page, the page will

again be fetched through the attacker's server. The victim remains trapped in the

attacker's false Web, and can follow links forever without leaving it.



2.3.4 Forms

If the victim fills out a form on a page in a false Web, the result appears to

be handled properly. Spoofing of forms works naturally because forms are

integrated closely into the basic Web protocols: form submissions are encoded in

URLs and the replies are ordinary HTML. Since any URL can be spoofed, forms

can also be spoofed.

When the victim submits a form, the submitted data goes to the attacker's

server. The attacker's server can observe and even modify the submitted data,

doing whatever malicious editing desired, before passing it on to the real server.

The attacker's server can also modify the data returned in response to the form

submission.

2.3.5 "Secure" connections don't help

One distressing property of this attack is that it works even when the

victim requests a page via a "secure" connection. If the victim does a "secure"

Web access (a Web access using the Secure Sockets Layer) in a false Web,

everything will appear normal: the page will be delivered, and the secure

connection indicator (usually an image of a lock or key) will be turned on.

What is SSL?

SSL stands for Secure Sockets Layer. This protocol, designed by

Netscape Communications Corp., is used to send encrypted HTTP (Web)

transactions.

Seeing "https" in the URL box on your browser means SSL is being used

to encrypt data as it travels from your browser to the server. This helps protect



sensitive information--social security and credit card numbers, bank account

balances, and other personal information--as it is sent.

The victim's browser says it has a secure connection because it does have

one. Unfortunately the secure connection is to www.attacker.org and not to the

place the victim thinks it is. The victim's browser thinks everything is fine: it was

told to access a URL at www.attacker.org so it made a secure connection to

www.attacker.org. The secure-connection indicator only gives the victim a false

sense of security.

2.3.5 Starting the Attack

To start an attack, the attacker must somehow lure the victim into the

attacker's false Web. There are several ways to do this.

1) An attacker could put a link to a false Web onto a popular Web page.

2) If the victim is using Web-enabled email, the attacker could email the

victim a pointer to a false Web, or even the contents of a page in a

false Web.

3) Finally, the attacker could trick a Web search engine into indexing part

of a false Web.

2.3.6 An example from real life

As web surfers and users we must always be wary of the content of the

web pages we surf, look for clues to spoofing, and report immediately to the

providers. NEVER click on link provided to you in an e-mail from someone you

don’t know or trust.



This is a very easy way to get you to that Hacker Intercept site! As an

example, let’s say you get the following e-mail from someone claiming to know

you.

Hi Johnny,

I found this new book on gardening on Amazon and I thought you would enjoy it.

Check it out...

Square Foot Gardening — Mel Bartholome

Love,

Mom

Close inspection of the link above provides the following:

http://www.amazone.com/exec/obidos/search-handleform/102-7984499-0468854

The link points to amazone.com instead of amazon.com. Everything else

in the link is genuine. So before buying this great new book recommended by

Mom, you’ll be stopping by and visiting the folks at amazone.com and giving

them your credit card number, expiration date, name, address and phone.

2.4 COMPLETING THE ILLUSION

The attack as described thus far is fairly effective, but it is not perfect.

There is still some remaining context that can give the victim clues that the

attack is going on. However, it is possible for the attacker to eliminate virtually

all of the remaining clues of the attack's existence.

Such evidence is not too hard to eliminate because browsers are very

customizable. The ability of a Web page to control browser behavior is often

desirable, but when the page is hostile it can be dangerous.



Another artifact of this kind of attack is that the pages returned by the

hacker intercept are stored in the user’s browser cache, and based on the

additional actions taken by the user; the spoofed pages may live on long after the

session is terminated.

2.4.1 The Status Line

The status line is a single line of text at the bottom of the browser window

that displays various messages, typically about the status of pending Web

transfers.

The attack as described so far leaves two kinds of evidence on the status

line. First, when the mouse is held over a Web link, the status line displays the

URL the link points to. Thus, the victim might notice that a URL has been

rewritten. Second, when a page is being fetched, the status line briefly displays

the name of the server being contacted. Thus, the victim might notice that

www.attacker.org is displayed when some other name was expected.

The attacker can cover up both of these cues by adding a JavaScript

program to every rewritten page. Since JavaScript programs can write to the

status line, and since it is possible to bind JavaScript actions to the relevant

events, the attacker can arrange things so that the status line participates in the

con game, always showing the victim what would have been on the status line in

the real Web. Thus the spoofed context becomes even more convincing.

2.4.2 The Location Line

The browser's location line displays the URL of the page currently being

shown. The victim can also type a URL into the location line, sending the

browser to that URL. The attack as described so far causes a rewritten URL to



appear in the location line, giving the victim a possible indication that an attack

is in progress.

This clue can be hidden using JavaScript. A JavaScript program can hide

the real location line and replace it by a fake location line which looks right and

is in the expected place. The fake location line can show the URL the victim

expects to see. The fake location line can also accept keyboard input, allowing

the victim to type in URLs normally. Typed-in URLs can be rewritten by the

JavaScript program before being accessed.

2.4.3 Viewing the Document Source

There is one clue that the attacker cannot eliminate, but it is very unlikely

to be noticed.

By using the browser's "view source" feature, the victim can look at the

HTML source for the currently displayed page. By looking for rewritten URLs in

the HTML source, the victim can spot the attack. Unfortunately, HTML source is

hard for novice users to read, and very few Web surfers bother to look at the



HTML source for documents they are visiting, so this provides very little

protection.

A related clue is available if the victim chooses the browser's "view

document information" menu item. This will display information including the

document's real URL, possibly allowing the victim to notice the attack. As

above, this option is almost never used so it is very unlikely that it will provide

much protection.

2.4.4 Bookmarks

There are several ways the victim might accidentally leave the attacker's

false Web during the attack. Accessing a bookmark or jumping to a URL by

using the browser's "Open location" menu item might lead the victim back into

the real Web. The victim might then reenter the false Web by clicking the "Back"

button. We can imagine that the victim might wander in and out of one or more

false Webs. Of course, bookmarks can also work against the victim, since it is

possible to bookmark a page in a false Web. Jumping to such a bookmark would

lead the victim into a false Web again.

2.5 WEB SPOOFING DEMONSTRATION

The HTML Source Code

<HTML>

<HEAD>

<TITLE>Web Spoofing Demonstration

</TITLE>

</HEAD>

<BODY onload=init()>

<HR>



<H2>Spoofing</H2>

<P>In both the cases below, if you mouse-over the link below, you'll see

“http://basement.dartmouth.edu" in the status line at the bottom of your screen.

<P>If you click on it, and you're not susceptible, then you'll actually go

there.

<P>If you click on it, and you are susceptible, then we'll pop open a new

window for you.

<P><A onclick="return openWin();

"href="http://basement.dartmouth.edu/"> Click here to see a spoof, if you're

configured correctly.</A></P>

<P><A onclick="javascript:openRealWin();return false;"

href="http://basement.dartmouth.edu/">Click here to see the real basement

site</A></P>

<P>

<HR>

</BODY>

</HTML>

The HTML Page as seen

Spoofing

In both the cases below, if you mouse-over the link below, you'll see

"http://basement.dartmouth.edu" in the status line at the bottom of your screen.

If you click on it, and you're not susceptible, then you'll actually go there.

If you click on it, and you are susceptible, then we'll pop open a new window for

you.

Click here to see a spoof, if you're configured correctly.


http://basement.dartmouth.edu/


Click here to see the real basement site

2.6 TRACING THE ATTACKER

Some people have suggested that this attack can be deterred by finding

and punishing the attacker. It is true that the attacker's server must reveal its

location in order to carry out the attack, and that evidence of that location will

almost certainly be available after an attack is detected.

Unfortunately, this will not help much in practice because attackers will

break into the machine of some innocent person and launch the attack there.

Stolen machines will be used in these attacks.

2.6.1 Remedies

Web spoofing is a dangerous and nearly undetectable security attack that

can be carried out on today's Internet. Fortunately there are some protective

measures you can take.

2.6.2 Short-term Solution

In the short run, the best defense is to follow a three-part strategy:

1. disable JavaScript in your browser so the attacker will be unable to hide

the evidence of the attack;

2. make sure your browser's location line is always visible;

3. pay attention to the URLs displayed on your browser's location line,

making sure they always point to the server you think you're connected to.


http://basement.dartmouth.edu/


This strategy will significantly lower the risk of attack, though you could

still be victimized if you are not conscientious about watching the location line.

At present, JavaScript, ActiveX, and Java all tend to facilitate spoofing and

other security attacks, so we recommend that you disable them. Doing so will

cause you to lose some useful functionality, but you can recoup much of this loss

by selectively turning on these features when you visit a trusted site that requires

them.

2.6.3 Long-term Solution

We do not know of a fully satisfactory long-term solution to this problem.

Changing browsers so they always display the location line would help, although

users would still have to be vigilant and know how to recognize rewritten URLs.

For pages that are not fetched via a secure connection, there is not much

more that can be done.

For pages fetched via a secure connection, an improved secure-connection

indicator could help. Rather than simply indicating a secure connection, browsers

should clearly say who is at the other end of the connection. This information

should be displayed in plain language, in a manner intelligible to novice users; it

should say something like "Microsoft Inc." rather than "www.microsoft.com."

Every approach to this problem seems to rely on the vigilance of Web

users. Whether we can realistically expect everyone to be vigilant all of the time

is debatable.



3.0 IP SPOOFING

3.1 TCP FLOODING

3.1.1 Introduction

When a system (called the client) attempts to establish a TCP connection

to a system providing a service (the server), the client and server exchange a set

sequence of messages. This connection technique applies to all TCP connec-

tions-telnet, Web, email, etc.

Examining the IP header, we can see that the first 12 bytes (or the top 3

rows of the header) contain various information about the packet. The next 8

bytes (the next 2 rows), however, contains the source and destination IP

addresses. Using one of several tools, an attacker can easily modify these

addresses – specifically the “source address” field. It's important to note that each

datagram is sent independent of all others due to the stateless nature of IP.

The client system begins by sending a SYN message to the server. The

server then acknowledges the SYN message by sending SYN-ACK message to

the client. The client then finishes establishing the connection by responding

with an ACK message. The connection between the client and the server is then

open, and the service-specific data can be exchanged between the client and the

server.

Here is a view of this message flow:



Client Server

------ ------

SYN-------------------->

<--------------------SYN-ACK

ACK-------------------->

Client and server can now send service-specific data

TCP uses sequence numbers. When a virtual circuit establishes between

two hosts, then TCP assigns each packet a number as an identifying index. Both

hosts use this number for error checking and reporting. Rik Farrow, in his article

"Sequence Number Attacks", explains the sequence number system as follows:

"The sequence number is used to acknowledge receipt of data. At the beginning

of a TCP connection, the client sends a TCP packet with an initial sequence

number, but no acknowledgment. If there is a server application running at the

other end of the connection, the server sends back a TCP packet with its own

initial sequence number, and an acknowledgment; the initial number from the

client's packet plus one. When the client system receives this packet, it must send

back its own acknowledgment; the server's initial sequence number plus one."

Thus an attacker has two problems:

1) He must forge the source address.

2) He must maintain a sequence number with the target.

The second task is the most complicated task because when target sets the

initial sequence number, the attacker must response with the correct response.

Once the attacker correctly guesses the sequence number, he can then

synchronize with the target and establish a valid session.

3.1.2 Services vulnerable to IP Spoofing:



Configuration and services that are vulnerable to IP spoofing:

RPC (Remote Procedure Call services)

Any service that uses IP address authentication

The X Window system

The R services suite (rlogin, rsh, etc.)

3.1.3 TCP and IP spoofing Tools:

1) Mendax for Linux

Mendax is an easy-to-use tool for TCP sequence number prediction and rshd

spoofing.

2)spoofit.h

spoofit.h is a nicely commented library for including IP spoofing functionality

into your programs. [Current URL unknown. -Ed.]

3) ipspoof

ipspoof is a TCP and IP spoofing utility.

4) hunt

hunt is a sniffer which also offers many spoofing functions.

5) dsniff

dsniff is a collection of tools for network auditing and penetration testing. dsniff,

filesnarf, mailsnarf, msgsnarf, urlsnarf, and webspy passively monitor a network

for interesting data (passwords, e-mail, files, etc.). arpspoof, dnsspoof, and macof

facilitate the interception of network traffic.

3.2 DESCRIPTION

3.2.1 TCP Flags

Flags are used to manage the establishment and shutdown of a virtual

circuit


http://www.monkey.org/~dugsong/dsniff/

http://www.ryanspc.com/sniffers/hunt-1.3.tgz

http://www.ryanspc.com/spoof/ipspoof.c

http://air.csc.ncsu.edu/xzhao/docs/DogPack/spoofers/sp/spoofit.h

http://rootshell.com/archive-j457nxiqi3gq59dv/199711/mendax_linux.tgz


o SYN: request for the synchronization of syn/ack numbers (used in

connection setup)

o ACK: states that the acknowledgment number is valid (all segments in a

virtual circuit have this flag set, except for the first one)

o FIN: request to shutdown one stream

o RST: request to immediately reset the virtual circuit.

3.2.2 TCP Virtual Circuit: Setup

A server, listening to a specific port, receives a connection request from a

client: The segment containing the request is marked with the SYN flag and

contains a random initial sequence number sc

The server answers with a segment marked with both the SYN and ACK

flags and containing

o an initial random sequence number ss

o sc + 1 as the acknowledgment number

The client sends a segment with the ACK flag set and with

sequence number sc+ 1 and acknowledgment number ss+ 1.



3.2.3 TCP Virtual Circuit: Data Exchange

A partner sends in each packet the acknowledgment of the previous

segment and its own sequence number increased by the number of

transmitted bytes

A partner accepts a segment from the other partner only if the numbers

match the expected ones

An empty segment may be used to acknowledge the received data.

The potential for abuse arises at the point where the server system has sent

an acknowledgment (SYN-ACK) back to client but has not yet received the ACK

message. This is what we mean by half-open connection. The server has built in

its system memory a data structure describing all pending connections. This data

structure is of finite size, and it can be made to overflow by intentionally creating

too many partially-open connections.



Creating half-open connections is easily accomplished with IP spoofing.

The attacking system sends SYN messages to the victim server system; these

appear to be legitimate but in fact reference a client system that is unable to

respond to the SYN-ACK messages. This means that the final ACK message will

never be sent to the victim server system.

The half-open connections data structure on the victim server system

will eventually fill; then the system will be unable to accept any new incoming

connections until the table is emptied out. Normally there is a timeout associated

with a pending connection, so the half-open connections will eventually expire

and the victim server system will recover. However, the attacking system can

simply continue sending IP-spoofed packets requesting new connections faster

than the victim system can expire the pending connections.



In most cases, the victim of such an attack will have difficulty in

accepting any new incoming network connection. In these cases, the attack does

not affect existing incoming connections nor the ability to originate outgoing

network connections. However, in some cases, the system may exhaust memory,

crash, or be rendered otherwise inoperative.

The location of the attacking system is obscured because the source

addresses in the SYN packets are often implausible. When the packet arrives at

the victim server system, there is no way to determine its true source. Since the

network forwards packets based on destination address, the only way to validate

the source of a packet is to use input source filtering.

3.3 IMPACT

Systems providing TCP-based services to the Internet community may be

unable to provide those services while under attack and for some time after the

attack ceases. The service itself is not harmed by the attack; usually only the

ability to provide the service is impaired.



In some cases, the system may exhaust memory, crash, or be rendered

otherwise inoperative.

3.3.1 TCP Virtual Circuit: Shutdown

One of the partners, say A, can terminate its stream by sending a segment

with the FIN flag set

The other partner, say B, answers with an ACK segment

From that point on, A will not send any data to B: it will just acknowledge

data sent by B

When B shutdowns its stream the virtual circuit is considered closed.



3.3.2 TCP Spoofing

Node A trusts node B (e.g., login with no password)

Node C wants to impersonate B with respect to A in opening a

TCP connection

C kills B (flooding, crashing, redirecting) so that B does not send

annoying RST segments

C sends A a TCP SYN segment in a spoofed IP packet with B’s address as

the source IP and sc as the sequence number

A replies with a TCP SYN/ACK segment to B with ss as the sequence

number. B ignores the segment: dead or too busy

C does not receive this segment but to finish the handshake it has to send

an ACK segment with ss + 1 as the acknowledgment number

o C eavesdrops the SYN/ACK segment

o C guesses the correct sequence number

3.4 REDUCING IP SPOOFED PACKETS



3.4.1 Be Un-trusting and Un-trustworthy

One easy solution to prevent this attack is not to rely on address-based

authentication. Disable all the r* commands, remove all .rhosts files and empty

out the /etc/hosts.equiv file. This will force all users to use other means of remote

access (telnet, ssh, skey, etc).

3.4.2 Packet Filtering

With the current IP protocol technology, it is impossible to eliminate IP-

spoofed packets. However, you can take steps to reduce the number of IP-

spoofed packets entering and exiting your network.

Currently, the best method is to install a filtering router that restricts the

input to your external interface (known as an input filter) by not allowing a

packet through if it has a source address from your internal network. In addition,

you should filter outgoing packets that have a source address different from your

internal network to prevent a source IP spoofing attack from originating from

your site.

The combination of these two filters would prevent outside attackers from

sending you packets pretending to be from your internal network. It would also

prevent packets originating within your network from pretending to be from

outside your network. These filters will *not* stop all TCP SYN attacks,

since outside attackers can spoof packets from *any* outside network, and

internal attackers can still send attacks spoofing internal addresses.

3.4.3 Cryptographic Methods



An obvious method to deter IP-spoofing is to require all network traffic to

be encrypted and/or authenticated. While several solutions exist, it will be a

while before such measures are deployed as defacto standards.

3.4.4 Initial Sequence Number Randomizing

Since the sequence numbers are not chosen randomly (or incremented

randomly) this attack works. Bellovin describes a fix for TCP that involves

partitioning the sequence number space. Each connection would have its own

separate sequence number space. The sequence numbers would still be

incremented as before, however, there would be no obvious or implied

relationship between the numbering in these spaces. Suggested is the following

formula:

ISN=M+F(localhost,localport,remotehost,remoteport)

Where M is the 4 microsecond timer and F is a cryptographic hash. F

must not be computable from the outside or the attacker could still guess

sequence numbers. Bellovin suggests F be a hash of the connection-id and a

secret vector (a random number, or a host related secret combined with the

machine's boot time).



4.0 DNS SERVER SPOOFING ATTACKS

The most complex attack is to alter the address the master DNS servers

will resolve for a given URL. The URL that an Internet user types in is not the

numeric address of the site required, but an alphanumeric address structure. The

DNS servers convert, say, www.articsoft.com, into a real Internet address, say

195.217.192.145 (not the correct address, but the point is made). This has to be

done because people don’t generally remember and associate 12 digit numbers

with anything except telephone numbers, and then they generally file them on the

telephone with a ‘friendly name’ that they have some relationship with. An

attack of this type has been successfully mounted that altered the server list, so

that, for a period of time, users requesting some sites were directed to the wrong

addresses.

This type of attack is a major threat and the Internet naming and

addressing authorities have taken it very seriously indeed. DNS servers have

incorporated numerous security measures to prevent repetitions of this attack

from being successful. These include having the servers mirror and monitor each

other as well as controlling very carefully how updates are introduced into the

servers.

This kind of problem can be resolved by positive site identification, where

the end user is able to automatically check the claimed web site URL against the

content provided.



5.0 CONCLUSION

When the world has started calling this era as the era of Internet – A

World Wide Web that connects the every nook and corner of the globe we should

never be let behind because of some pestering security problems.

Spoofing of the Web and IP has over the years proved to be annoying as

well as dangerous. In this tense scenario it is mandatory that we stick onto the

various solutions so far available and at the same time spend our sincere efforts

in devising better plans to solve this menace. Indeed techniques like Packet

Filtering and Cryptographic techniques help to some extend but their efficiency

is limited. We still rely on manual security checks of the status line, location line

etc. which indeed are quite ineffective and practical.

The whole problem basically exists in that most of the web applications

and tools rely on the source IP address authentication. Alternatives are to be

derived and a better safer Internet should solve the problem of Spoofing.

---------------------------------



6.0 REFERENCES

IP Spoofing

1. www.cert.org

2. www.securityfocus.com

3. www.webopedia.com

4. www.linuxgazatte.com

5. www.networkice.com

Web Spoofing

1. www.cs.princeton.edu

2. www.cs.dartmouth.edu

3. www.fbi.gov

4. www.systemexperts.com

5. www.spoonybard.nu



ABSTRACT

This paper describes an Internet security attack that could endanger the

privacy of World Wide Web users and the integrity of their data. The attack can

be carried out on today's systems, endangering users of the most common Web

browsers, including Netscape Navigator and Microsoft Internet Explorer.

Spoofing means pretending to be something you are not. In Internet

terms it means pretending to be a different Internet address from the one you

really have in order to gain something. That might be information like credit

card numbers, passwords, personal information or the ability to carry out actions

using someone else’s identity. IP spoofing attack involves forging one's source

address. It is the act of using one machine to impersonate another.








……………………………



CONTENTS

1.0 INTRODUCTION

1.1 HISTORY

1.2 WHAT IS SPOOFING?

2.0 WEB SPOOFING

2.1 INRTODUCTION

2.2 SPOOFING ATTACKS

2.3 WEB SPOOFING

2.4 COMPLETING THE ILLUSION

2.5 WEB SPOOFING DEMONSTRATION

2.6 TRACING THE ATTACKER

3.0 IP SPOOFING

3.1 TCP FLOODING

3.2 DESCRIPTION

3.3 IMPACT

3.4 REDUCING IP SPOOFED PACKETS

4.0 DNS SPOOFING ATTACKS

5.0 CONCLUSION

6.0 REFERENCES

………………………..



ACKNOWLEDGMENT

I express my sincere thanks to Prof. M.N Agnisarman Namboothiri

(Head of the Department, Computer Science and Engineering, MESCE),

Mr. Sminesh (Staff incharge) for their kind co-operation for presenting the

seminar.

I also extend my sincere thanks to all other members of the faculty of

Computer Science and Engineering Department and my friends for their

co-operation and encouragement.

Nandakumar.V


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