XSS (Cross-Site Scripting)

XSS (Cross-Site Scripting) is a type of web security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. This vulnerability can be exploited to steal sensitive information, such as user credentials, cookies, or other private data, as well as to perform actions on behalf of the victim, such as sending unauthorized messages or making fraudulent transactions.

The basic idea behind XSS attacks is that a web application fails to properly sanitize user input, allowing an attacker to inject code that is executed in the victim’s browser. There are several types of XSS attacks, including:

1. Reflected XSS: In a reflected XSS attack, the attacker sends a malicious script to the web application, which then reflects it back to the victim’s browser. This can happen, for example, when the application fails to properly validate user input in a search field or a comment section.

2. Stored XSS: In a stored XSS attack, the attacker injects malicious code into a web page or a database, which is then retrieved and executed by the victim’s browser. This can happen, for example, when the application fails to properly validate user input in a user profile or a message board.

3. DOM-based XSS: In a DOM-based XSS attack, the attacker injects malicious code into the Document Object Model (DOM) of a web page, which is then executed by the victim’s browser. This can happen, for example, when the application uses client-side scripting to process user input.

To prevent XSS attacks, web developers need to implement several security measures, such as input validation, output encoding, and content security policies (CSPs). Input validation ensures that user input is properly sanitized before being used by the application, while output encoding ensures that any data output by the application is properly encoded to prevent malicious code injection. CSPs provide an additional layer of protection by restricting the sources of content that a web page can load. Additionally, users can protect themselves from XSS attacks by keeping their web browsers and other software up-to-date and by using browser extensions that block malicious scripts.