The two-volume set LNCS 15747 and 15748 constitutes the refereed conference proceedings of the 12nd International Conference on Detection of Intrusions and Malware, and Vulnerability Assessment, DIMVA 2025, held in Graz, Austria, during July 9-11, 2025. The 25 revised full papers and 11 posters are presented in these proceedings were carefully reviewed and selected from 103 submissions. The papers are organized in the following topical sections: Part I: Web Security; Vulnerability Detection; Side channels; and Obfuscation. Part II: AI/ML & Security; Android & Patches; OS & Network; and Resilient Systems.