Description: The XSS (Cross-Site Scripting) vulnerability is a type of security vulnerability found in web applications that allows attackers to inject client-side scripts into web pages viewed by other users. This script injection can lead to various malicious actions, such as stealing cookies, impersonating users, redirecting to malicious sites, or executing unauthorized actions on behalf of the affected user. XSS vulnerabilities are generally classified into three types: reflected XSS, stored XSS, and DOM-based XSS. Reflected XSS occurs when the malicious script is sent through an HTTP request and reflected in the server’s response. Stored XSS, on the other hand, involves the script being stored on the server and delivered to users accessing the affected page. Finally, DOM-based XSS occurs when the script executes in the user’s browser without server interaction. The relevance of this vulnerability lies in its ability to compromise user security and the integrity of web applications, making it a common target for attackers and a focal point for security professionals.
History: The XSS vulnerability was first identified in the late 1990s when developers began to notice that scripts could be injected into web applications. In 2000, the term ‘Cross-Site Scripting’ was formalized, and techniques began to be developed to mitigate this type of attack. Over the years, the security community has worked on creating standards and best practices to prevent XSS, such as using Content Security Policies (CSP) and proper input validation.
Uses: XSS vulnerabilities are primarily used by attackers to steal sensitive information, such as user credentials and session cookies. They can also be employed to carry out phishing attacks, redirect users to malicious sites, or execute unauthorized actions on web applications. Developers and security professionals use knowledge about XSS to implement defense measures and protect web applications.
Examples: An example of reflected XSS is when a user clicks on a link containing a malicious script in the URL, causing the script to execute in their browser. A case of stored XSS could be a comment on a forum that contains a script, which executes every time another user visits the comment page. Regarding DOM-based XSS, an example would be a website that modifies the browser’s DOM to include a malicious script based on user input without proper validation.
