T 5.28 Denial of services

A denial of service (DoS) attack is intended to prevent users from using functions or devices that are normally available to them. This type of attack is often connected to the use of distributed resources, with the attacker placing such high demands on these resources that other users are prevented from carrying out their work. For example, a shortage of the following resources can be artificially induced: processes, CPU time, disk space, inodes, or directories.

This can be caused, for example,

• by starting a large number of programs simultaneously,
• by simultaneously starting up numerous programs which consume a lot of CPU time,
• by allocating all the free inodes on a UNIX system so that no new files can be created,

• through uncoordinated allocation of tape units in z/OS systems so that applications have to wait for free tape units and online processing is limited,

• by deliberately entering incorrect passwords (also using scripts) with the objective of blocking all user IDs on a z/OS system,
• by sending data packets constructed in a certain way that can cause malfunctions on the recipient's computer due to software vulnerabilities,
• by deliberately overloading the network, and
• by cutting off network connections.