HTML5 introduced powerful features that enhanced the functionality and user experience of web applications. However, these capabilities also expanded the attack surface, making web applications vulnerable if security controls are not properly implemented. Attackers exploit HTML5 APIs and browser features to compromise confidentiality, integrity, and availability of web applications. Therefore, understanding HTML5-based attacks and implementing appropriate security measures are essential aspects of web application testing and security auditing. One common HTML5 attack involves Cross-Site Scripting (XSS). HTML5 supports dynamic content and client-side scripting, allowing attackers to inject malicious JavaScript into web pages. Once executed in a victim's browser, the script can steal session cookies, capture user credentials, manipulate web content, or redirect users to malicious websites. Improper input validation and output encoding significantly increase the risk of XSS attacks. Another major threat is Cross-Origin Resource Sharing (CORS) misconfiguration. HTML5 allows controlled communication between different origins using CORS. If servers are incorrectly configured to allow unrestricted access, attackers can send unauthorized requests, access sensitive information, or exploit authenticated user sessions. The Web Storage API, including Local Storage and Session Storage, is another target. HTML5 enables browsers to store large amounts of client-side data. Developers sometimes store authentication tokens, personal information, or sensitive application data in Local Storage without encryption. If an attacker successfully performs XSS, the stored information can be easily accessed and