"`` Access control in Express Node.js applications is critical to web applications built with the Express framework, ensuring users can access only the data and functionality they're authorized to use. However, broken access control vulnerabilities can occur when there are flaws in the application's implementation of these access control rules, allowing unauthorized users to access sensitive information or perform restricted actions. Broken vertical access control occurs when a regular user gains access to admin-level features or other privileges when they shouldn't have that access, while horizontal access control issues occur when a user gains access to resources or data that belong to other users of the same level. To prevent these vulnerabilities, it's essential to use the latest versions of libraries, avoid security-through-obscurity methods, apply the principle of least privilege, conduct thorough audits and tests, and leverage tools such as Snyk's Visual Studio Code extension to detect and fix broken access control vulnerabilities in real-time. By implementing these strategies, developers can significantly enhance their application's security and maintain the integrity of their applications and data.