Within the context of the next-generation open radio access network (O-RAN), this paper provides a thorough analysis of xApps and their security. This research is anticipated to have a major impact on improving the security requirements and operational effectiveness of xApps. A wide range of subjects are covered in this paper, such as how xApps are built inside the O-RAN architecture, what security risks and vulnerabilities they provide, and how to reduce them. Through an examination of their architecture, vulnerabilities, and major security issues, it seeks to increase our understanding of xApps and make them more resilient. It addresses specific security issues including protecting the E2 interface and protecting against adversarial attacks and unwanted access to machine learning-based xApps. Additionally, the study explores the origins of vulnerabilities in xApps, such as compromised xApps, malicious xApps, and external agents. The mitigation strategies for xApps involve leveraging xApps to enhance O-RAN interface security, implementing centralized and distributed security measures, and adopting the xApp Repository Function (XRF) framework for authentication.