XS leaks are a class of web security vulnerabilities that allow hackers to obtain sensitive information from a user's browsing session on other websites or web apps by exploiting inherent browser functionalities and side channels, bypassing security restrictions imposed by Same Origin Policy (SOP) and Cross-Origin Resource Sharing (CORS). XS leak attacks can lead to severe consequences such as disclosure of sensitive information, session hijacking, and undermining trust in online platforms and services. To mitigate the risk of XS leak attacks, best practices include implementing a strong Content Security Policy (CSP), enforcing the SameSite attribute for cookies, minimizing the use of sensitive data in URLs, applying rate limiting, using proper CORS configurations, and integrating security tools such as Snyk Code to identify and fix vulnerabilities.