Cross-Site Scripting (XSS) is a type of security vulnerability that occurs when an attacker injects malicious scripts into web pages that are then viewed by other users. This can happen when a web application does not properly validate or sanitize user input before including it in the output it generates.
There are three main types of XSS attacks:
Stored XSS (Persistent XSS): In this scenario, the malicious script is permanently stored on the target server. It is then served to users whenever they access a particular page or resource, making it a persistent threat. For example, an attacker might inject a script into a forum post or a comment on a website.
Reflected XSS (Non-Persistent XSS): In this case, the injected script is included in the URL and is reflected off the web server to the user’s browser. The user typically receives a malicious link and, when they click on it, the script is executed. Reflected XSS attacks are often embedded in phishing emails or malicious websites.
DOM-based XSS: This type of XSS involves the manipulation of the Document Object Model (DOM) in a user’s browser. Instead of exploiting a vulnerability on the server, the attacker manipulates the client-side code, making changes to the DOM and causing unintended behavior.
Impact of XSS Attacks:
Session hijacking: Attackers can steal session cookies, allowing them to impersonate users and perform actions on their behalf.
Defacement of websites: Attackers may modify the content of web pages to display offensive or misleading information.
Theft of sensitive information: Malicious scripts can capture keystrokes or other sensitive data entered by users on compromised pages.
Distribution of malware: Attackers can use XSS to deliver and execute malware on users’ devices.
To prevent XSS attacks, developers should implement proper input validation and output encoding. Input validation ensures that user input meets the expected criteria, while output encoding ensures that any user input displayed on a web page is properly encoded to prevent script execution. Additionally, the use of secure coding practices, such as Content Security Policy (CSP), can help mitigate the risk of XSS attacks.