A method for DoS attacks at an NF includes maintaining, at a first NF, an NF subscription database containing rules that specify maximum numbers of allowed subscriptions and corresponding rule criteria. The method further includes receiving, at the first NF and from a second NF, a subscription request for establishing a subscription. The method further includes determining, by the first NF, that the subscription request matches criteria for at least one rule in the NF subscription database and incrementing, by the first NF, at least one count of a number of subscriptions for the at least one rule. The method further includes determining, by the first NF, that the at least one count of the number of subscriptions exceeds a maximum number of allowed subscriptions for the at least one rule. The method further includes, in response to determining that the at least one count of the number of subscriptions exceeds the maximum number of allowed subscriptions for the at least one rule, preventing establishment of the subscription.