Abstract-Wireless sensor networks can be deployed in inhospitable terrains or in hostile environments to provide continuous monitoring and processing capabilities. Due to the wireless and distributed nature, security is very crucial issue in wireless sensor network. Security comes from attacks. Detecting wormhole attack is very hard compared to other attacks because it uses private, out-of-band channel to launch the attack. To launch this type of attack, attacker does not require any cryptographic breaks. Wormhole attack represents one forms of Denial of Service attack. It is a gateway of many more attacks. This paper focuses on the various wormhole detection techniques, the open research areas and future research directions.Keywords: Wireless sensor network, security, distributed, wormhole, out-of-band. I. INTRODUCTION Wireless sensor network consists of large number of sensor nodes. Each sensor node consists of processor, analog to digital converter, transceiver and battery. Sensor nodes are densely deployed. They use broadcast communication primitive. Sensor nodes rely on wireless channels for transmitting and receiving data from other nodes [1,2]. Sink node is the data aggregation point. Wireless sensor networks that are capable of observing the environment, processing data and making decisions based on these observations [3][4][5][6]. These networks are important for a number of applications such as coordinated target detection and localization, surveillance and environment monitoring.Providing security services in sensor networks turns out to be a very challenging task. First, sensor nodes usually have very limited resources such as storage, bandwidth, computation and energy. It is often undesirable to implement expensive algorithms on sensor nodes. Second, sensor nodes are usually deployed in unattended environment. An attacker can easily capture and compromise a few sensor nodes without being noticed. When sensor nodes are compromised, the attacker can learn all the secrets stored on them and launch a variety of attacks [7][8][9][10][11][12]. Thus any security mechanism for sensor networks has to be resilient to compromised sensor nodes. Third, most sensor applications are based on local computation and communication, while adversaries are usually much more powerful and resourceful than sensor nodes.Wireless sensor networks are vulnerable to many attacks, but among all the attacks wormhole attack is very dangerous. Two malicious nodes are located far away and create a high speed tunnel [13][14][15]. At one ends of the tunnel, one malicious node receives the traffic and forwards it to the end of the tunnel to the other malicious node. It is also possible that packet is altered that contains different information. The packets pass through the tunnel can propagate faster compared to the normal path. To launch the attack, attacker does not require knowing the protocols used in the network or the services offered in the network.The rest of the paper is organized as follows. In section 2 we have discussed the ...