  The current security problems in cyberspace are characterized by strong and
complex threats. Defenders face numerous problems such as lack of prior
knowledge, various threats, and unknown vulnerabilities, which urgently need
new fundamental theories to support. To address these issues, this article
proposes a generic theoretical model for cyberspace defense and a new mimic
defense framework, that is, Spatiotemporally heterogeneous, Input aware, and
Dynamically updated Mimic Defense (SIDMD). We make the following contributions:
(1) We first redefine vulnerabilities from the input space perspective to
normalize the diverse cyberspace security problem. (2) We propose a novel
unknown vulnerability discovery method and a dynamic scheduling strategy
considering temporal and spatial dimensions without prior knowledge.
Theoretical analysis and experimental results show that SIDMD has the best
security performance in complex attack scenarios, and the probability of
successful attacks is greatly reduced compared to the state-of-the-art.
