We design the optimal jamming attack strategy for a cognitive radio network in the presence of path-loss decaying signal models. We consider a cognitive radio network with K participating cognitive radios and one fusion center in the presence of one primary user and one jammer in the operating region. We assume that the network is not aware of the presence of the jammer and hence employs the optimal decision rules designed for a benign environment. Jammer, on the other hand, tries to take advantage of this ignorance and carries the best possible attack so that it can maximally deteriorate the global performance (error-probability) of the network under a total power-constraint. We consider a two-fold attack - one on the CR (sensor) reception and other on the fusion center reception. We present numerical results depicting near-field and far-field effects over different path-loss exponents to find the optimal jamming attack for a relatively simple example where the network has only one sensor (K=1). This example serves as an illustration of the basic concepts and will be followed by a more in-depth study.