Summary: Program bugs remain a major challenge for software developers and various tools have been proposed to help with their localisation and elimination. Most present-day tools are based either on over-approximating techniques that can prove safety but may report false positives, or on under-approximating techniques that can find real bugs but with possible false negatives. In this paper, we propose a dual static analysis that is based only on over-approximation. Its main novelty is to concurrently derive conditions that lead to either success or failure outcomes and thus we provide a comprehensive solution for both proving safety and finding real program bugs. We have proven the soundness of our approach and have implemented a prototype system that is validated by a set of experiments.