What is Cross-Site Scripting (XSS) ?

Cross-Site Scripting (XSS) is a type of security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. This can be done by exploiting a weakness in the way the website processes user input. When a user visits a compromised web page, the malicious code is executed in their browser, giving the attacker the ability to steal sensitive information, such as login credentials, or perform other malicious actions, such as redirecting the user to a phishing website.

There are two types of XSS: stored and reflected.

Stored XSS is when the malicious script is permanently stored on the website's server, and is served to every user who views the affected page. This type of attack is more dangerous as it can potentially affect a large number of users.

Reflected XSS is when the malicious script is temporarily reflected off of the website and sent to the user's browser through a URL or a form submission. This type of attack requires the user to interact with the injected script, such as clicking on a link or submitting a form.

XSS attacks can be delivered via various methods, such as injecting a script into a search field or crafting a link that contains the malicious code. For example, an attacker may create a link that contains a script that steals the user's cookies when clicked, and then send this link to the victim via email or social media.

To prevent XSS attacks, web developers should validate and sanitize user input, use a Content Security Policy, and escape special characters in user input.

Input validation and sanitization: This involves checking user input for any potentially harmful characters or patterns and removing or encoding them.

Content Security Policy (CSP): This is a security feature that allows website owners to specify which sources of content are allowed to be loaded by the browser.

Escaping special characters: This involves converting certain characters, such as < and >, so that they are not interpreted as HTML or JavaScript code by the browser.

By implementing these measures, web developers can help protect their users from XSS attacks and other types of malicious code injection.