- Internet & the Web
Different Types of Network Attacks And Security Threats and Counter Measures
A Network attack or security or security incident is defined as a threat, intrusion, denial of service or other attack on a network infrastructure that will analyze your network and gain information to eventually cause your network to crash or to become corrupted. In many cases, the attacker might not only be interested in exploiting software applications, but also try to obtain unauthorized access to network devices. Unmonitored network devices are the main source of information leakage in organizations. In most organizations, every email message, every web page request, every user logon, and every transmittable file is handled by a network device. Under some setups, telephone service and voice messaging are also handled by network devices. If the attacker is able to "own" your network devices, then they "own" your entire network. Network attacks cut across all categories of software and platform type.
There are at least seven types of network attacks.
- DoS and DDoS.
- Social engineering.
1. Spoofing (Identity spoofing or IP Address Spoofing)
Any internet connected device necessarily sends IP datagrams into the network. Such internet data packets carry the sender's IP address as well as application-layer data. If the attacker obtains control over the software software running on a network device, they can then easily modify the device's protocols to place an arbitrary IP address into the data packet's source address field. This is known as IP spoofing, which makes any payload appear to come from any source. With a spoofed source IP address on a datagram, it is difficult to find the host that actually sent the datagram.
The countermeasure for spoofing is ingress filtering. Routers usually perform this. Routers that perform ingress filtering check the IP address of incoming datagrams and determine whether the source addresses that are known to be reachable via that interface. If the source addresses that are known to be reachable via that interface. If the source address is not in the valid range, then such packets will be discarded.
Packet sniffing is the interception of data packets traversing a network. A sniffer program works at the Ethernet layer in combination with network interface cards (NIC) to capture all traffic traveling to and from internet host site. Further, if any of the Ethernet NIC cards are in promiscuous mode, the sniffer program will pick up all communication packets floating by anywhere near the internet host site. A sniffer placed on any backbone device, inter-network link or network aggregation point will therefore be able to monitor a whole lot of traffic. Most of packet sniffers are passive and they listen all data link layer frames passing by the device's network interface. There are dozens of freely available packet sniffer programs on the internet. The more sophisticated ones allow more active intrusion.
The key to detecting packet sniffing is to detect network interfaces that are running in promiscuous mode. Sniffing can be detected two ways:
- Host-based : Software commands exist that can be run on individual host machines to tell if the NIC is running in promiscuous mode.
- Network-based : Solutions tend to check for the presence of running processes and log files, which sniffer programs consume a lot of. However, sophisticated intruders almost always hide their tracks by disguising the process and cleaning up the log files.
The best countermeasure against sniffing is end-to-end or user-to-user encryption.
3. Mapping (Eavesdropping)
Before attacking a network, attackers would like to know the IP address of machines on the network, the operating systems they use, and the services that they offer. With this information, their attacks can be more focused and are less likely to cause alarm. The process of gathering this information is known as mapping.
In general, the majority of network communications occur in an unsecured or "clear text" format, which allows an attacker who has gained access to data paths in your network to "listen in" or interpret the traffic. When an attacker is eavesdropping on your communications, it is referred to as sniffing or snooping. The ability of an eavesdropper to monitor the network is generally the biggest security problem that administrators face in an enterprise.
Counter measures are strong encryption services that are based on cryptography only. Otherwise your data can be read by others as it traverses the network.
4. Hijacking (man-in-the-middle attack)
This is a technique that takes advantage of a weakness in the TCP/IP protocol stack, and the way headers are constructed. Hijacking occurs when someone between you and the person with whom you are communicating is actively monitoring, capturing, and controlling your communication transparently. For example, the attacker can re-route a data exchange. When computers are communicating at low levels of the network layer, the computers might not be able to determine with whom they are exchanging data.
Man-in-middle attacks are like someone assuming your identity in order to read your message. The person on the other end might believe it is you, because the attacker might be actively replying as you, to keep the exchange going and gain more information.
These are programs that look like ordinary software, but actually perform unintended or malicious actions behind the scenes when launched. Most remote control spyware programs are of this type. The number of trojan techniques are only limited by the attacker's imagination. A torjanizes file will look, operate, and appear to be the same size as the compromised system file.
The only protection is early use of a cryptographic checksum or binary digital signature procedure.
6. Denial-of-Service attack (DoS) and Distributed-Denial-of-Service (DDoS)
A denial of service attack is a special kind of Internet attack aimed at large websites. It is a type of attack on a network that is designed to bring the network to its knees by flooding it with useless traffic. Denial of Service can result when a system, such as a Web server, has been flooded with illegitimate requests, thus making it impossible to respond to real requests or taks. Yahoo! and e-bay were both victims of such attacks in February 2000.
A Dos attack can be perpetrated in a number of ways. There are three basic types of attack.
- Consumption of computational resources, such as band width, disk space or CPU time.
- Disruption of configuration information, such as routing information.
- Disruption of physical network components.
The consequences of a DoS attack are the following:
- Unusually slow network performance.
- Unavailability of a particular web site.
- Inability to access any web site.
- Dramatic increase in the amount of spam you receive in your account.
Common forms of denial of service attacks are,
a) Buffer Overflow Attacks
The most common kind of DoS attack is simply to send more traffic to a network address than the programmer's expectation on size of buffers. A few of the better known attacks based on the buffer characteristics of a program or system include:
- Sending e-mail messages that have attachments with 256 character file names to Netscape and Microsoft mail programs.
- Sending over sized Internet Control Message Protocol (ICMP) packets.
- Ending to a user of an e-mail program a message with a "From" address longer than 256 characters.
b) Smurf Attack
In this attack, the perpetrator sends an IP ping request to a receiving site. The ping packet specifies that, it is broadcast to a number of hosts within the receiving site's local network. The packet also indicates that the request is from another site, which is the target site that is to receive the denial of service attack. The result will be lots of ping replies flooding back to the innocent, spoofed host. If the flood is great enough, the spoofed host will no longer be able to receive or distinguish real traffic.
c) SYN floods
When a computer wants to make a TCP/IP connection to another computer, usually a server, an exchange of TCP/SYN and TCP/ACK packets of information occur. The computer requesting the connection, usually the client's or user's computer, sends a TCP/SYN packet which asks the server if it can connect. If the server is ready, it sends a TCP/SYN-ACK packet back to the client to say "Yes, you may connect" and reserves a space for the connection, waiting for the client to respond with a TCP/ACK packet. In a SYN flood, the address of the client is often forged so that when the server sends a TCP/SYN-ACK packet back to the client, the message is never received from client because the client either doesn't exist or wasn't expecting the packet and subsequently ignores it. This leaves the server with a dead connection, reserved for a client that will never respond. Usually this is done to one server many times in order to reserve all the connections for unresolved clients, which keeps legitimate clients from making connections.
Distributed Denial-of-Service attacks (DDoS)
A distributed denial of service attack (DDoS) occurs when multiple compromised sysrems or multiple attackers flood the band width or resources of a targeted system with useless traffic. These systems are compromised by attackers using a variety of methods.
In DDoS attacks, the attacker first gains access to user accounts on numerous hosts across the Internet. The attacker then installs and runs a slave program at each compromised site that quietly waits for commands from a master programs running, the master program then contacts the slave programs, instructing each of them to launch a denial-of-service attack directed at the same target host. The resulting coordinated attack is particularly devastating, since it comes from so many attacking hosts at the same time.
Here also ingress filtering only can control DoS attack and that too to a small extent.
7. Social Engineering
Social engineering is the use of persuasion or deception to gain access to information systems. The medium is usually a telephone or e-mail message. The attacker usually pretends to be a director or manager in the company traveling on business with a deadline to get some important data left on their network drive. They pressure the help desk to give them the toll-free number of the RAS server to dial and some times get their password reset. The main purpose behind social engineering is to place the human element in the network-breaching loop and use it as a weapon. The human element has been referred to as the weakest link in network security.
Examples of social engineering.
- Faked Email : The social engineer sends a message to one or more users in a domain that "this is the system administrator and your password must be reset to user 123 " for a temporary period of time. The hacker then continuously monitors for the change and then exploits the whole system.
- Fictitious Competition : The social engineer manipulates a group of users to participate in some fake competition for a jackpot prize, with the ultimate purpose of eventually extracting confidential information about network and password security.
- The Helpful Help Desk : The help desk gets a call from the social engineer impersonating a user reporting a forgotten password. In many cases the help desk will change the user's password over the phone. The hacker now has a legitimate user name and password to work with. To avoid problems from the original user, the social engineer will then call the user who was impersonated and say something like " This is Vivek from MIS department. We had some problems with security today, so we have changed your password. Your new password is angel123."
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