This paper highlights the importance of synthetic data generation for sensitive data sharing and analyzes vulnerabilities in diffusion models that generate tabular data. Specifically, it points out that membership inference attacks (MIA) can allow models to memorize training data and leak sensitive information. MIA-EPT is a novel black-box attack specialized for tabular data that masks and reconstructs attributes to construct error-based feature vectors to reveal membership signals. MIA-EPT demonstrates generalizability across multiple diffusion models using only synthetic data output, achieving second place in the MIDST 2025 competition.