Ethereum is one of the top blockchain platforms that represents this second generation of blockchain technology. However, the security vulnerabilities associated with smart contracts pose significant risks to confidentiality, integrity, and availability of applications supported by Ethereum. While several studies have enumerated various security issues in smart contracts, only a handful have identified the factors that determine the severity and potential of these issues to pose significant risks in practice. As its first contribution, this thesis presents a framework that identifies such factors and highlights the most critical security threats and vulnerabilities of Ethereum smart contracts. To achieve this, we conduct a comprehensive literature review to identify and categorize the vulnerabilities, assess their potential impact, and evaluate the likelihood of exploitation in real-life contracts. We classify the identified vulnerabilities based on their nature and severity and proposed mitigation recommendations. Our theoretical contribution is to establish a correlation between the security vulnerabilities of smart contracts and their potential impact on the security of smart contracts by identifying factors that pose a (practical) threat.

Our practical contribution involves developing a tool based on staticanalysis that can automatically detect at least one critical securityissue with the highest threat factor. For the target vulnerability, wechoose the usage of input from external users without any validation.This vulnerability, as we call it, Missing Input Validation (MIV), actsas a root cause for further (well-known and well-researched) issues,for instance, the flow of tainted values into sensitive operations suchas the transfer of cryptocurrencies and self destruct instruction. Weimplement the tool MIV Checker and evaluate its efficacy on a test setof 36 smart contracts. Our evaluation results show that MIV Checkercorrectly detects 87.6 % of instances of MIV in the dataset.