What is Cross-site Scripting (XSS)?
Cross-site scripting (XSS) is a type of cyber attack that involves injecting malicious code into a website or web application. This code is then executed by the victim's web browser, allowing the attacker to gain access to the victim's personal information, steal sensitive data, or perform other malicious actions. In this write-up, we will take a look at the history of XSS, how it was used in the early days, the technologies that are vulnerable to it, and how individuals and organizations can protect themselves against it.
History of Cross-site Scripting
Cross-site scripting was first identified as a security vulnerability in the late 1990s, and it has since become one of the most common types of cyber attacks. The first recorded instance of XSS was in 1995, when a researcher named Robert Tappan Morris used it to inject a malicious script into a web forum, causing it to crash.
In the early days of XSS, attackers primarily used it to deface websites or to redirect victims to malicious websites. However, as the technology has evolved, so have the capabilities of XSS attacks. Today, XSS is often used for more sophisticated purposes, such as stealing sensitive data, installing malware, or performing phishing attacks.
Technologies Vulnerable to XSS
XSS attacks can be launched against a wide range of technologies, including web applications, websites, and even mobile apps. Any technology that allows users to input data or that displays data from external sources is potentially vulnerable to XSS.
Web applications are particularly vulnerable to XSS attacks because they often accept user input and display it to other users. For example, a social media platform might allow users to post comments or create profiles, which are then displayed to other users. If an attacker is able to inject a malicious script into one of these inputs, it could be executed by other users, allowing the attacker to steal sensitive data or perform other malicious actions.
Websites can also be vulnerable to XSS attacks if they allow users to input data or display data from external sources. For example, a news website might allow users to post comments or submit articles, which are then displayed to other users. If an attacker is able to inject a malicious script into one of these inputs, it could be executed by other users, allowing the attacker to steal sensitive data or perform other malicious actions.
Mobile apps can also be vulnerable to XSS attacks if they accept user input or display data from external sources. For example, a messaging app might allow users to send messages to each other, which are then displayed to the recipient. If an attacker is able to inject a malicious script into one of these messages, it could be executed by the recipient, allowing the attacker to steal sensitive data or perform other malicious actions.
Protection Against Cross-site Scripting
Given the widespread nature of XSS attacks and the potential damage they can cause, it is important for individuals and organizations to take steps to protect themselves against them. Here are some ways to do this:
Input validation: One of the most effective ways to protect against XSS attacks is to implement input validation. This involves checking user input for any potentially malicious code before it is accepted by the system.
Output encoding: Output encoding is another effective way to protect against XSS attacks. This involves converting potentially malicious code into a harmless format before it is displayed to the user.
Content Security Policy: A Content Security Policy (CSP) is a security feature that can be implemented on a website or web application to help prevent XSS attacks. A CSP specifies which sources of content are allowed to be loaded by the web browser, helping to block any malicious content.
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