Landslide events often occur after rainfall events during which the pore water pressure builds up within surficial soil layers, leading to shallow slope failure. The spatial variability of the permeability parameters of the soil causes high gradients in pore water pressure when the rainwater infiltrates into the slope. In this paper, we compute the reliability of infinite slopes under random rainfall events considering the spatial variability of the soil permeability. We model the infiltration process in HYDRUS-1D, which applies a numerical solution of Richard's equation, and combine this with a one-dimensional random field model of the hydraulic conductivity of the soil. The rainfall event is characterized in terms of its duration and average intensity and modeled through a self-similar random process. The reliability analysis of the infinite slope is based on the factor of safety concept for evaluating slope stability. To cope with the large number of random variables arising from the discretization of the random fields, we evaluate the slope reliability through subset simulation, which is an adaptive Monte Carlo method known to be especially efficient for such high dimensional problems. We study the influence of the duration and average intensity of the rainfall event on the slope reliability.