## 4 Devices' Vulnerabilities and Requirements
### Classification of IoT Security Attacks on Different Layers of IoT Networks
#### 4.6.3 Network Attacks
In this attack, legitimate users are unable to use network resources to access information as all available resources are exhausted, which makes network resources unavailable to users. Moreover, many users' unencrypted data can also be exposed [133,134]. * Sinkhole Attack: In a sinkhole attack, an adversary deceives the system by luring all data flow from neighboring WSN nodes into a metaphorical blackhole; the system is fooled into believing the data has already arrived its endpoint. The attacker uses a compromised node to attract network traffic by transmitting fraudulent routing information. The goal of the attacker is to breach the system's integrity as well as disrupting network service. It prevents all packets from transferring, resulting in a sink or black hole in the network [135,136]. * Routing Information Attacks: In a routing information attack, the adversary uses a compromised node or a group of compromised nodes to make or change the routing information. The purpose of the attack is to obfuscate the system and make routing loops, permit or reject traffic, change the destination, provide fake error messages, shorten or extend source paths, or even partition the network; e.g., Hello Attack and Blackhole Attack [84,137]. * Sybil Attack: Sybil attacks are more common in networks with a large number of clients. A single node that unlawfully acquires the identities of numerous other nodes is referred to as a malicious node. The attacker uses the identities of the other nodes, causing the adjacent nodes to receive phony and incorrect information. The attacker can part in the distributed algorithm, such as the election where one sybil node has an identity more than once. It can also be selected as a part of the routing path, which can lead to a longer routing distance [138,139,140]. * Replay Attack: Attackers get information by eavesdropping on the messages of two parties, and the malicious node resends old packets to the overall system as broadcast or sent to a specific set of devices. When the other nodes receive these messages, they update their routing tables according to this expired information and reply regardless of whether the sender is transmitting any new packets or not. The Routing table and network topology will also be outdated, and with a huge number of packets replayed, both bandwidth and power will be consumed. This will result in the network's activities being terminated sooner than expected, facilitating the impersonation attacks [20; 86]. * HELLO flood attack: Some WSN routing protocols broadcast the \"HELLO\" packet to advertise themselves to their neighbors and construct a network topology. The attacker does not need to send legitimate traffic to conduct this attack. It can subsequently rebroadcast overhead packets with sufficient strength to deliver to every other network interface, leaving the network in disarray [141]. Though the malicious node is far away from network nodes, every node in the network will be convinced that the attacker is nearby. The majority of protocols that are impacted by this kind of attack depend on nearby nodes exchanging localized information to maintain topology or control flow. * Blackmail attack: In the blackmail attack, a compromised node eliminates a legitimate node from the network by proclaiming that the legitimate node is a malicious node. If a compromised node is able to block a large number of nodes, the network will become unstable [142; 143]. * Blackhole attack: In this attack, a malicious node, instead of forwarding all the packets, may drop those, and it may drop all the data traffic around the malicious node. This attack is also referred to as \"Selfishness\". Its impact is highest if the malicious node is a sinkhole [110]. * Wormhole attack: A wormhole attack necessitates the collaboration of two or more adversaries with excellent communication resources (e.g., power, bandwidth) and the ability to construct better communication lines (called \"tunnels\") between them.