Practice shows that even the most secure software written by the best engineers contain bugs. Malware is not an exception. In most cases their authors do not follow the best secure software development practices thereby introducing an interesting attack scenario which can be used to stop or slow-down malware spreading, defend against DDoS attacks and take control over C&Cs and botnets. Several previous researches have demonstrated that such bugs exist and can be exploited. To find those bugs it would be reasonable to use coverage-guided fuzzing. This talk aims to answer the following two questions: ___ we defend against malware by exploiting bugs in them ? How can we use fuzzing to find those bugs automatically ? The author will show how we can apply coverage-guided fuzzing to automatically find bugs in sophisticated malicious samples such as botnet Mirai which was used to conduct one of the most destructive DDoS in history and various banking trojans. A new cross-platform tool implemented on top of WinAFL will be released and a set of 0day vulnerabilities will be presented. Do you want to see how a small addition to HTTP-response can stop a large-scale DDoS attack or how a smart bitflipping can cause RCE in a sophisticated banking trojan? If the answer is yes, this is definitely your talk.