Cross-site scripting (XSS) attacks are a type of security vulnerability typically found in web applications. They enable attackers to inject malicious scripts into web pages viewed by other users. There are three main types of XSS attacks:
Stored XSS (also known as Persistent XSS): In this type of attack, the malicious script is permanently stored on the target server, typically in a database, message forum, visitor log, or comment field. When a user visits the affected web page, the malicious script is served to the user's browser. An example would be if an attacker posts a comment on a blog with a malicious script embedded in it. Any user reading that comment would execute the script.
Reflected XSS (also known as Non-Persistent XSS): This type of attack involves the malicious script being reflected off the web server as a response to a request, usually in the form of an error message or search result. The script is not stored on the server but is included in the URL or input data. An example is if a user clicks on a malicious link in an email that directs them to a legitimate website with a reflected XSS vulnerability, executing the script when the page loads.
DOM-based XSS: This type of attack occurs when the vulnerability exists in client-side code rather than server-side code. The attacker's payload is executed because modifying the DOM (Document Object Model) environment in the victim's browser is used to execute malicious scripts. An example is if a web page dynamically updates its content based on user input without properly sanitizing it, allowing an attacker to inject and execute a script.
To mitigate these types of attacks, developers should implement proper input validation and output encoding, use secure coding practices, and consider deploying web application firewalls (WAFs) or using cloud-based security services that can help protect against XSS attacks. For instance, Tencent Cloud offers a Web Application Firewall service that can help detect and block XSS attacks among other web-based threats.