Home > Articles

This chapter is from the book

Attacks

Due to the anonymity of networks and the Internet, we are seeing an increase in attacks on all types of servers. The reasons for such attacks can be attributed to anything from simple curiosity to malicious intent.

In an effort to prevent your network from becoming part of the growing number of statistics, you need to recognize when an attack is happening and take the proper steps to end it. Learning to identify which types of attacks you might be subject to and how to implement proper security to protect your environment are important functions of your position. Some of the more common attacks are listed in this section.

Denial of Service (DoS) and Distributed Denial of Service (DDoS) Attacks

The purpose of a denial of service (DoS) attack is to disrupt the resources or services that a user would expect to have access to. These types of attacks are executed by manipulating protocols and can happen without the need to be validated by the network.

Many of the tools used to produce this type of attack are readily available on the Internet. Administrators use them to test connectivity and troubleshoot problems on the network, whereas malicious users use them to cause connectivity issues.

Here are some examples of DoS attacks:

  • Smurf/smurfing—This attack is based on the Internet Control Message Protocol (ICMP) echo reply function. It is more commonly known as ping, which is the command-line tool used to invoke this function. In this attack, the attacker sends ping packets to the broadcast address of the network, replacing the original source address in the ping packets with the source address of the victim, thus causing a flood of traffic to be sent to the unsuspecting network device.

  • Fraggle—This attack is similar to a Smurf attack. The difference is that it uses the User Datagram Protocol (UDP) instead of ICMP. The attacker sends spoofed UDP packets to broadcast addresses as in the Smurf attack. These UDP packets are directed to port 7 (echo) or port 19 (chargen). When connected to port 19, a character generator attack can be run. Table 3.1 lists the most commonly exploited ports.

  • Ping flood—This attack attempts to block service or reduce activity on a host by sending ping requests directly to the victim. A variation of this type of attack is the ping of death, in which the packet size is too large and the system doesn't know how to handle the packets.

  • SYN flood—This attack takes advantage of the TCP three-way handshake. The source system sends a flood of synchronization (SYN) requests and never sends the final acknowledgment (ACK), thus creating half-open TCP sessions. Because the TCP stack waits before resetting the port, the attack overflows the destination computer's connection buffer, making it impossible to service connection requests from valid users.

  • Land—This attack exploits a behavior in the operating systems of several versions of Windows, Unix, Macintosh OS, and Cisco IOS with respect to their TCP/IP stacks. The attacker spoofs a TCP/IP synchronization (SYN) packet to the victim system with the same source and destination IP address and the same source and destination ports. This confuses the system as it tries to respond to the packet.

  • Teardrop—This form of attack targets a known behavior of UDP in the TCP/IP stack of some operating systems. The Teardrop attack sends fragmented UDP packets to the victim with odd offset values in subsequent packets. When the operating system attempts to rebuild the original packets from the fragments, the fragments overwrite each other, causing confusion. Because some operating systems cannot gracefully handle the error, the system will most likely crash or reboot.

  • Bonk—This attack affects mostly Windows machines by sending corrupt UDP packets to DNS port 53. This causes confusion, and the system crashes.

  • Boink—This is a Bonk attack that targets multiple ports instead of just port 53.

CAUTION

You should know the difference between the various types of attacks and the ports they are executed on.

Table 3.1 Commonly Exploited Ports

Port

Service

7

Echo

11

Systat

15

Netstat

19

Chargen

20

FTP-Data

21

FTP

22

SSH

23

Telnet

25

SMTP

49

TACACS

53

DNS

80

HTTP

110

POP3

111

Portmap

161/162

SNMP

443

HTTPS

1812

RADIUS


Another form of attack is a simple expansion of a DoS attack, referred to as a Distributed DoS (DDoS) attack. There is already downloadable software that allows DDoS attacks to be generated from inside the network. This will allow disgruntled or malicious users to disrupt services without any outside influence. The attacker distributes zombie software that allows the attacker partial or full control of the infected computer system. Once an attacker has enough systems compromised with the installed zombie software, he can initiate an attack against a victim from a wide variety of hosts. The attacks come in the form of the standard DoS attacks, but the effects are multiplied by the total number of zombie machines under the control of the attacker.

To help protect your network, you can set up filters on external routers to drop packets involved in these types of attacks. You should also set up another filter that denies traffic originating from the Internet that shows an internal network address. When you do this, the loss of ping and some services and utilities for testing network connectivity will be incurred, but this is a small price to pay for network protection. If the operating system allows it, you should reduce the amount of time before the reset of an unfinished TCP connection. This will make it harder to keep resources unavailable for extended periods of time.

TIP

In the case of a DDoS attack, your best weapon is to get in touch quickly with your upstream ISP and see whether it can divert traffic or block the traffic at a higher level.

Subscribing to newsgroups and checking security Web sites daily ensures that you keep up with the latest attacks and exploits. Applying the manufacturer's latest operating system patches or fixes can also help prevent attacks.

Back Door

A back door is a program that allows access to a system without using security checks. Usually programmers put back doors in programs so they can debug and change code during test deployments of software. Because many of these back doors are undocumented, they may get left in, causing security risks.

Some of the better-known software programs that can be used as back doors include the following:

  • Back Orifice—This is a remote administration tool that allows system administrators to control a computer from a remote location (that is, across the Internet). It is construed as a dangerous back door designed by a group called the Cult of the Dead Cow Communications. Back Orifice consists of two main pieces: a client application and a server application. The client application, running on one machine, can be used to monitor and control a second machine running the server application.

  • NetBus—Like Back Orifice, NetBus allows a remote user to access and control a machine via the Internet. NetBus runs under the Windows NT operating system as well as Windows 95/98. NetBus also has two essential parts: a server (the part that resides on the victim's system) and a client (the application used to find and control the server). Features and functions vary, but the result is much the same—loss of privacy and security on a computer anytime it is connected to the Internet.

  • Sub7 (or SubSeven)—This is a Windows 9X Internet backdoor Trojan similar to Back Orifice and NetBus. When it is running, anyone running the appropriate client software has unlimited access to the system while it is connected to the Internet.

NOTE

The following are legitimate products that may be installed by malicious users to cause harm:

Virtual Network Computing (VNC)—This is remote control software by AT&T labs that allows you to view a desktop environment from anywhere on the Internet and from a wide variety of machine architectures.

PCAnywhere—This product is produced by Symantec. It is remote control software with encryption and authentication. It is used by many companies in their help desk departments for resolving user issues.

Terminal Services—This application is used by Microsoft operating systems for remote control. It delivers the Windows desktop and applications by means of terminal emulation.

CAUTION

Back Orifice, NetBus, and Sub7 have two essential parts: a server and client. The server is the infected machine and the client is used for remote-controlling the server. These programs are known as illicit servers.

As with most utilities, the software in the preceding list can be used with good intent or maliciousness. The best ways to prevent backdoor attacks are user education and software monitoring. Users should be instructed to only download software off the Internet that has been approved by network or security administration and from approved sites. Installation and use of software such as antivirus packages can catch many of these backdoor applications, including Back Orifice, NetBus, and Sub7. Be sure your antivirus software is scheduled to download the latest virus definitions at least weekly.

Another type of back door comes in the form of a privileged user account. An existing user who already has privileges often creates the backdoor account. This account is set up to look like a normal user's account and given a high-level privilege. This allows the user or an attacker to come in under an alias. To prevent this situation, you need to set proper access so users will not have the right or privilege to alter operating system files—know who has administrative rights. Auditing, covered in the last section of this chapter, can help detect the creation and use of backdoor accounts by tracking the creation of these accounts and their frequency of use.

Spoofing

Spoofing is making data appear to come from somewhere other than where it really originated. This is accomplished by modifying the source address of traffic or source of information. Spoofing seeks to bypass IP address filters by setting up a connection from a client and sourcing the packets with an IP address that is allowed through the filter.

Services such as email, Hypertext Transfer Protocol (HTTP), and File Transfer Protocol (FTP) can also be spoofed. Web spoofing happens when an attacker creates a convincing but false copy of an 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. In email spoofing, a spammer or a computer virus can forge the email packet information in an email so that it appears the email is coming from a trusted host, from one of your friends, or even from your own email address. If you leave your email address at some Internet site or exchange email with other people, a spoofer may be able to use your email address as the sender address to send spam. These forms of attacks are often used to get additional information from network users in order to complete a more aggressive attack.

As mentioned earlier, you should set up a filter that denies traffic originating from the Internet that shows an internal network address. Using the signing capabilities of certificates on servers and clients allows Web and email services to be more secure. The use of IPSec can secure transmissions between critical servers and clients. This will help prevent these types of attacks from taking place.

Man in the Middle

The man-in-the-middle attack takes place when an attacker intercepts traffic and then tricks the parties at both ends into believing that they are communicating with each other. The attacker can also choose to alter the data or merely eavesdrop and pass it along. This attack is common in Telnet and wireless technologies. It is also generally difficult to implement because of physical routing issues, TCP sequence numbers, and speed. Because the hacker has to be able to sniff both sides of the connection simultaneously, programs such as Juggernaut, T-Sight, and Hunt have been developed to help make the process easier.

If the attack is attempted on an internal network, physical access to the network will be required. Be sure that access to wiring closets and switches is restricted—if possible, the area should be locked. After you have secured the physical aspect, the services and resources that allow a system to be inserted into a session should be protected. DNS can be compromised and used to redirect the initial request for service, providing an opportunity to execute a man-in-the-middle attack. DNS access to should be restricted to read-only for everyone except the administrator. The best way to prevent these types of attacks is to use encryption and secure protocols.

CAUTION

A man-in-the-middle attack takes place when a computer intercepts traffic and either eavesdrops on the traffic or alters it.

Replay

In a replay attack, packets are captured by using sniffers. After the pertinent information is extracted, the packets are placed back on the network. This type of attack can be used to replay bank transactions or other similar types of data transfer in the hopes of replicating or changing activities, such as deposits or transfers.

Protecting yourself against replay attacks involves some type of timestamp associated with the packets or time-valued, nonrepeating serial numbers. Secure protocols such as IPSec prevent replays of data traffic in addition to providing authentication and data encryption.

TCP/IP Hijacking

Hijacking is the term used when an attack takes control of a session between the server and a client. This starts as a man-in-the-middle attack and then adds a reset request to the client. The result is that the client gets kicked off the session, while the rogue machine still communicates with the server. This commonly happens during Telnet and Web sessions where security is lacking or when session timeouts aren't configured properly.

Forcing a user to reauthenticate before allowing transactions to occur could help prevent this type of attack. Other protection mechanisms include the use of unique initial sequence numbers (ISNs) and Web session cookies.

Weak Keys

Weak keys generally denote a weak choice in the number of combinations during encryption. This is usually found in the block cipher method used in 40-bit and 56-bit encryption, whereby the messages are broken into blocks that are independent of each other.

Mathematical

A mathematical attack on an algorithm uses the mathematical properties of the algorithm to decrypt data using computations that are more efficient than guessing. They can come in the form of ciphertext-only, plaintext, or chosen plaintext attacks. These concepts are explained in greater detail in Chapter 8, "Basics of Cryptography."

The best way to avoid weak key, birthday (discussed later), and mathematical attacks is to use 128-bit encryption. Both 40-bit and 56-bit encryption have already been broken—40-bit in less than four hours. Keep in mind that export laws prohibit strong encryption from being exported, resulting in many vulnerable servers.

Password Guessing

Allowing users to choose their own passwords produces an unsecure environment because users typically choose passwords that are easy-to-remember words. On the other end of the spectrum, if the passwords are too difficult to remember, users will write them down and post them on monitors, keyboards, and any number of easy-to-find places. Secure passwords should consist of uppercase and lowercase letters, numbers, and special characters. The two basic types of attacks on passwords are brute-force and dictionary attacks. Passwords can also be guessed by shoulder surfing, which is looking over a person's shoulder and watching as she types.

TIP

When allowing users to choose their own passwords, you might to have them combine the first letters and dates of important events. An example would be "My daughter Diane was born on Jan 1, 1976." The password would be MdDwbJ11976.

Brute Force

Brute force is a term used to describe a way of cracking a cryptographic key or password. It involves systematically trying every conceivable combination until a password is found, or until all possible combinations have been exhausted. The more complex the password is, the longer it takes to crack. Many programs exist that try to guess passwords or decipher password files.

Dictionary

We tend to choose passwords that have special meaning to us or relate to our everyday lives. This makes them easy to crack because they are usually found in the dictionary. A dictionary attack is the first step of a brute-force attack. This type of attack checks through known words in a dictionary data file trying to match the password.

Birthday

Birthday attacks are a type of brute-force technique that uses hash functions. It gets its name from the probability that two or more people in a group of 23 sharing the same birthday is greater than 50%.

Some of the more popular password guessing programs include:

  • Crack—A password-cracking program designed to quickly locate insecurities in Unix (or other) password files by scanning the contents of a password file.

  • John the Ripper—A password cracker currently available for Unix, DOS, and Windows NT/95. It has its own modules for different ciphertext formats and architectures.

  • L0phtCrack—A Windows and Unix password-auditing tool that produces user passwords from the cryptographic hashes that are stored by the operating system.

The following are measures you can use to help reduce the use of brute-force password-guessing tools:

  • Make the password length at least eight characters and require the use of uppercase and lowercase letters, numbers, and special characters.

  • Lock user accounts out after three to five failed logon attempts. This stops programs from deciphering the passwords on locked accounts.

  • Monitor the network for the use of questionable tools. If password files can be captured, they can be run though password-guessing programs on another machine.

CAUTION

Passwords should be at least eight characters in length and possess a combination of uppercase and lowercase letters, numbers, and special characters.

Software Exploitation

Software exploitation takes advantage of a program's flawed code. One of the most used flaws is the buffer overflow. When more data is sent to a buffer than it is able to handle, it doesn't know how to react to the extra data. Usually this crashes the system and leaves it in a state where arbitrary code can be executed or an intruder can function as an administrator.

In the case of buffer overflow, good quality assurance and secure programming practices would definitively thwart this type of attack. The most effective way to prevent an attacker from exploiting software bugs is to keep the manufacturer's latest patches and service packs applied as well as monitor the Web for newly discovered vulnerabilities.

Pearson IT Certification Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Pearson IT Certification and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Pearson IT Certification products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.pearsonitcertification.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020