The goal of Domain Generation Algorithm (DGA) detection is to recognize
infections with bot malware and is often done with help of Machine Learning
approaches that classify non-resolving Domain Name System (DNS) traffic and are
trained on possibly sensitive data. In parallel, the rise of privacy research
in the Machine Learning world leads to privacy-preserving measures that are
tightly coupled with a deep learning model's architecture or training routine,
while non deep learning approaches are commonly better suited for the
application of privacy-enhancing methods outside the actual classification
module. In this work, we aim to measure the privacy capability of the feature
extractor of feature-based DGA detector FANCI (Feature-based Automated Nxdomain
Classification and Intelligence). Our goal is to assess whether a data-rich
adversary can learn an inverse mapping of FANCI's feature extractor and thereby
reconstruct domain names from feature vectors. Attack success would pose a
privacy threat to sharing FANCI's feature representation, while the opposite
would enable this representation to be shared without privacy concerns. Using
three real-world data sets, we train a recurrent Machine Learning model on the
reconstruction task. Our approaches result in poor reconstruction performance
and we attempt to back our findings with a mathematical review of the feature
extraction process. We thus reckon that sharing FANCI's feature representation
does not constitute a considerable privacy leakage.