The analysis of approaches to assessing the vulnerability of complex network systems and indicators used to measure the effect of external influences on the nodes and connections of the network is carried out. The problem of blocking target objects of the system by constructing cross-sections using the developed practical algorithms is considered. A probabilistic modeling algorithm is proposed to construct cross-sections. For the selection of cross-sections that cause the maximum number of outages of non-target consumers, indicators of the availability of nodes and cross-sections to resource sources are proposed. An example of the application of these indicators is given, illustrating the selection of blocking cross-sections on a typical IEEE scheme.