Cyber security risk assessments provide a crucial starting point towards the understanding of existing risk exposure, via which suitable mitigation strategies can be formed. Risk is viewed as a product of threat, vulnerability and impact, and equal understanding of each of these elements is vitally important. This can be a challenge in Industrial Control System (ICS) environments, where adopted technologies are typically not only bespoke, but interact directly with the physical world. To date, existing vulnerability identification has focused on traditional vulnerability categories. While this approach provides risk assessors with a baseline understanding and the ability to hypothesize about potential resulting impacts, it is rather high level, operating at a level of abstraction that would be viewed as incomplete within a traditional information system context. The work presented in this paper takes the understanding of ICS device vulnerabilities a step deeper. It offers a tool, PLC-VBS, that helps identify Programmable Logic Controller (PLC) vulnerabilities, specifically within logic used to monitor, control, and automate operational processes. PLC-VBS gives risk assessors a more coherent picture about the potential impact should the identified vulnerabilities be exploited; this applies specifically to operational process elements.