Vulnerability assessment activities usually analyze new security advisories over current running systems. However, a system compromised in the past by a vulnerability unknown at that moment may still constitute a potential security threat in the present. Accordingly, past unknown system exposures are required to be taken into account. We present in this paper a novel approach for increasing the overall security of computing systems by identifying past hidden vulnerable states. In that context, we propose a modeling for detecting unknown past system exposures as well as an OVAL-based distributed framework for autonomously gathering network devices information and automatically analyzing their past security exposure. We also describe an implementation prototype and evaluate its performance through an extensive set of experiments.