What is the Cross-site scripting (XSS) attack?

Cross-site scripting (XSS) attack is a client-side code injection attack

Cross-site scripting (XSS) attack is a web security vulnerability attack, or it's often termed as the client-side code injection attack. In this case, the attacker executes malicious scripts in a web browser that seems to be a benign and trusted website at first glance. Here, the webpage/website acts as the driver to deliver the malicious scripts to the user’s system.

Wondering how does XSS or cross-site scripting works?

Well, this serious security flaw happens when a vulnerable web site is manipulated so that it can execute malicious JavaScript to the users' browsers. And, when this malicious code gets executed inside a victim's browser, the attacker can completely compromise the interaction with the application. An attacker will use XSS in order to send malicious code to a targeted user. The problem is that the user's system (i.e., browser) won't be able to find out that this piece of code is wrongful and should never be trusted. Instead, the browser of the targeted end-user will execute the malicious code considering that it belongs to a trusted and reliable source.

Once the malicious code is executed, the script will get access to various sensitive information stored by a user's browser, such as session tokens, cookies, login credentials, saved passwords, and more. What's more, these scripts are so powerful that they can even tamper and rewrite the contents of an HTML web page.

Although cross-site scripting attacks can occur on any webpage, it's most common for the following sites, such as message boards and online forums, where the users can enter inputs and comments. A website becomes vulnerable to XSS if it uses and allows unsanitized user input. Note, XSS attacks can be possible through malicious code execution of Flash, ActiveX, VBScript, CSS, and JavaScript, etc. Among these, JavaScript cross-site scripting attacks are the most common type of attack that the users can experience.

XSS attack works on a two-step process. First of all, the attacker attempts to find out a source to inject the malicious code to a webpage/website that the victim visits.

Now, if the victim user browses the web page having the malicious code and executes it unknowingly, the XSS security attack will tamper the essential information of a browser.

Types of Cross-site scripting (XSS) attacks

There are three types of cross-site scripting (XSS) attacks, such as Reflected XSS, Stored XSS, and DOM-based XSS.

Reflected XSS is considered to be the simplest form of XSS attack where the malicious script is sent and executed from the HTTP request. Now, a stored XSS attack is possible when the malicious code snippet is sent from a website's database. Similarly, a DOM-based XSS attack happens when vulnerability/flaw exists in the client-side code.

Impacts of Cross-site scripting (XSS) attacks

In web applications that hold confidential and sensitive data like e-commerce applications, banking transactions, healthcare records, and emails, the impact of XSS will be quite serious. But, this impact is subjected to a single targeted victim user.

But, if the XSS attacker gets elevated privileges/full control of the application through malicious code injection, then the impact will be very severe and critical as it will be able to target and compromise the security of all users and their corresponding data.

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