One common method of attack involves saturating the target (victim) machine with external communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consuming its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.Denial-of-service attacks are considered violations of the IAB’s Internet proper use policy, and also violate the acceptable use policies of virtually all Internet Service Providers. They also commonly constitute violations of the laws of individual nations. (Source: http://en.wikipedia.org/wiki/Denial-of-service_attack)

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Common DoS Attacks

• Filling hard drive space with e-mail attachments
• Sending a message that resets a targets host subnet mask causing routing disruption
• Using up all the target’s resources to accept network connections

Additional DoS Attacks

• Buffer Overflow Attack
  • When a process receives much more data that expected
  • Since buffers are created to contain a finite amount of data, the extra information, which has to go somewhere – can overflow in adjacent buffers, corrupting or overwriting the valid data held in them
  • PING – Packet Internet Groper – uses ICMP – Internet Control Message Protocol
  • PING of Death – Intruder sends a PING that consists of an illegally modified and very large IP datagram, thus overfilling the system buffers and causing the system to reboot or hang
• SYN Attack
  • Attacks the buffer space during a TCP handshake
  • Attacker f;ppds the target system’s “in-process” queue with connection requests causing the system to timeout
• Teardrop Attack
  • Modifying the length of the fragmentation fields in the IP packet
  • When a machine receives this attack, it is unable to handle the data and can exhibit behavior ranging from a lost Internet connection to the infamous BSOD, the machine becomes confused and crashes
• Smurf Attack
  • Source site sends spoofed network requests to a large network (bounce site) and all machines responds to a target site
  • Exploits IP broadcast addressing
• Fraggle Attack
  • “Cousin” of the Smurf Attack
  • uses UDP echo packets in the same fashion as the ICMP echo packet