Security tools, using static code analysis, are employed to find common bug classes, such as SQL injections and cross-site scripting vulnerabilities. This paper focuses on another bug class that is related to the object-pool pattern, which allows objects to be reused over multiple sessions. We show that the pattern is applied in a wide range of Java Enterprise frameworks and describe the problem of inter-session data flows, which comes along with the pattern. To demonstrate that the problem is relevant, we analyzed different open-source and a proprietary commercial software, with the help of a detection approach we introduce. We were able to show that the problem class occurred in these applications and posed a threat to the confidentiality of the closed-source software.