The maximum likelihood attack strategy is known to be the optimal attack strategy for an eavesdropper in a wiretap channel scenario with additive white Gaussian noise channels under the distinguishing security criterion. The main drawback of this optimal attack is its high computational complexity. While this complexity doesn’t hinder the eavesdropper since he has unlimited computing power, it does present a significant challenge for legitimate parties. For them, it is extremely difficult, if not impossible, to estimate the outcome of the optimal attacker strategy to validate the secrecy of their communication system. In this paper, we introduce a low complexity method for generating upper and lower bounds on the attack performance of the eavesdropper to validate the security against the maximum likelihood attack strategy. We theoretically establish that the derived bounds represent valid constraints on the attack success probability under suitable constraints. The validation method is based on list generation and can be used for any linear block code. Furthermore, we propose a list generation algorithm for this validation method and show different ways to further reduce the complexity. We compare the proposed validation method with state-of-the-art attack strategies in numerical simulations for various error-correcting codes.