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DOS Attacks

Denial of service (DOS) attack, a type of attack on a network that is designed to bring the network to its knees by flooding it with useless traffic. Many DoS attacks, such as the Ping of Death and Teardrop attacks, exploit limitations in the TCP/IP protocols.

Teardrop attack is type of attack where fragmented packets are forged to overlap each other when the receiving host tries to reassemble them.

Ping of death type of DoS attack in which the attacker sends a ping request that is larger than 65,536 bytes, which is the maximum size that IP allows. While a ping larger than 65,536 bytes is too large to fit in one packet that can be transmitted, TCP/IP allows a packet to be fragmented, essentially splitting the packet into smaller segments that are eventually reassembled. Attacks took advantage of this flaw by fragmenting packets that when received would total more than the allowed number of bytes and would effectively cause a buffer overload on the operating system at the receiving end, crashing the system. Ping of death attacks are rare today as most operating systems have been fixed to prevent this type of attack from occurring. 
DDOS Attack: A distributed denial of service attack (DDoS) occurs when multiple systems flood the bandwidth or resources of a targeted system, usually one or more web servers. This is the result of multiple compromised systems (for example a botnet) flooding the targeted system(s) with traffic. When a server is overloaded with connections, new connections can no longer be accepted.

Peer to Peer Attack Attackers have found a way to exploit a number of bugs in peer-to-peer servers to initiate DDoS attacks. Peer-to-peer attacks are different from regular botnet-based attacks. With peer-to-peer there is no botnet and the attacker does not have to communicate with the clients it subverts. Instead, the attacker acts as a "puppet master," instructing clients of large peer-to-peer file sharing hubs to disconnect from their peer-to-peer network and to connect to the victim's website instead. As a result, several thousand computers may aggressively try to connect to a target website. While peer-to-peer attacks are easy to identify with signatures, the large number of IP addresses that need to be blocked (often over 250,000 during the course of a large-scale attack) means that this type of attack can overwhelm mitigation defenses.

For all known DOS attacks, there are software fixes that system administrators can install to limit the damage caused by the attacks.

A permanent Denial Of Service (PDOS), also known as "Phlashing". It's an attack that damages a system so badly that it requires replacement or reinstallation of hardware. Phlashing used for hardware attack. Unlike the distributed denial-of-service attack, a PDoS attack exploits security flaws which allow remote administration on the management interfaces of the victim's hardware, such as routers, printers, or other networking hardware. The attacker uses these vulnerabilities to replace a device's firmware with a modified, corrupt, or defective firmware image a process which when done legitimately is known as flashing. This therefore "bricks" the device, rendering it unusable for its original purpose until it can be repaired or replaced.

The PDOS is a pure hardware targeted attack which can be much faster and requires fewer resources than using a botnet in a DDoS attack. Because of these features, and the potential and high probability of security exploits on Network Enabled Embedded Devices (NEEDs), this technique has come to the attention of numerous hacker communities. PhlashDance is a tool created by Rich Smith (an employee of Hewlett-Packard's Systems Security Lab) used to detect and demonstrate PDoS vulnerabilities at the 2008 EUSecWest Applied Security Conference in London. Smith said remotely abusing firmware update mechanisms with a Phlashing attack, for instance, is basically a one-shot attack. “Phlashing attacks can achieve the goal of disrupting service without ongoing expense to the attacker; once the firmware has been corrupted, no further action is required for the DOS condition to continue,”

An attacker could use remote firmware update paths in network hardware, which are often left unprotected, to deliver corrupted firmware and flash this to the device. As a result, the device would become unusable.

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