Fog is a cloud that closes to the ground. The components of fog and cloud complement each other. These components provide mutually beneficial interdependent services for communication, processing, control, and storage across the network. Attacking the fog nodes are as important as attacking the cloud. Since the fog node has more limited resources, it is more targeted by intruders. In addition, fog nodes are more attractive to attackers because they have less computing power and are located closer to the attacker than the cloud. But the key point is that access to limited resources makes it easier to save the fog node because the fog does not have the complexities of the cloud, and it is easy to run an intrusion detection system on it. In this article, focusing on the resource limitation in the fog node, we will invent a method to save the fog node. In the proposed method, the support vector machines (SVMs) technique is used. Among the advantages of using the support vector machine, we can mention not being trapped in local optima, solving the over fitting problem, and ease of working with high-dimensional data. Based on the research, support vector machine is the most widely used machine learning method for Internet of Things security articles in the literature. In this article, in order to conduct tests, according to published global statistics, the most important category of web attacks, i.e. SQL injection attacks, is considered. The average detection accuracy is obtained and the results of the evaluations indicate the acceptable efficiency of the proposed method.