MANETs or Mobile Ad Hoc Networks is a network that consists of mobile nodes, is selforganizing and short lived. Due to the openness, decentralized and infrastructure less architecture it can be prone to different types of attacks. One such attack is the JellyFish attack. It is a type of passive attack .It is very difficult to detect this attack as it complies with the protocols. In this paper we present a study on this attack and its variants. The first section gives a brief introduction on MANETs and the different types of attacks on it from different point of view. The later section we concentrate on the JellyFish Attack. Further a review on the analysis is carried out from different sources to understand the impact of this attack on the performance and its effect on the network. Keywords: Active attacks, Passive Attacks, JellyFish Attack, AODV, DSR, TORA, GRP