9 Attack techniques
9.2 Active attacks

Active attacks attempt to alter system resources or affect their operation. This type of attack is one where the adversary attempts to delete, add, or in some other way alter the transmission on the channel. An active attacker threatens data integrity and authentication as well as confidentiality.

Active attacks involve some modification of the data stream or the creation of a false stream and can be divided into six categories:

- Masquerade. It is a type of attack where the attacker pretends to be an authorized user of a system in order to gain access to it or to gain greater privileges than they are authorized for.
- Replay. In this kind of attack, a valid data transmission is maliciously or fraudulently repeated or delayed. This is carried out either by the originator or by an adversary who intercepts the data and retransmits them, possibly as part of a masquerade attack.
- Modification of messages. The attacker removes a message from the network traffic, alters it, and reinserts it.
- Man in the Middle (MitM). In this kind of attacks, an intruder intercepts communications between two parties, usually an end user and a website. The attacker can use the information accessed to commit identity theft or other types of fraud.
- Denial of Service (DoS) and Distributed Denial of Service (DDoS). A denial of service (DoS) attack is an incident in which a user or organization is deprived of the services of a resource they would normally expect to have. In a distributed denial-of-service, large numbers of compromised systems (sometimes called a botnet) attack a single target.
- Advanced Persistent Threat (APT). It is a network attack in which an unauthorized person gains access to a network and stays there undetected for a long period of time. The intention of an APT attack is to steal data rather than cause damage to the network or organization. APT attacks target organizations in sectors with high-value information, such as national defense, manufacturing and the financial industry.