What Is Cross-Site Scripting?

Cross-Site Scripting (XSS) is a web security vulnerability that happens when cybercriminals inject client-side scripts into web pages accessible by other users. These scripts compromise the web page and allow cybercriminals to inject malicious scripts into a user’s browser, leading to the exposure of data, session hijacking or manipulation of the web page’s content and functionality.

Continue reading to learn more about cross-site scripting and how you can keep yourself protected from it. 

How Does Cross-Site Scripting Work?

Cross-site scripting works by cybercriminals injecting malicious scripts into a website’s content, often in places like comment sections or input fields. When other users later access these compromised web pages, their browsers unintentionally execute the injected scripts, allowing the cybercriminals to perform actions like stealing user data, manipulating page content or redirecting users to harmful websites. 

Types of Cross-Site Scripting

There are three different types of cross-site scripting: reflected XSS, persistent XSS and DOM-based XSS.

Reflected XSS

Reflected XSS occurs when a cybercriminal injects malicious scripts into a website address or input field that is immediately reflected back to the user by the web page. When the user clicks the manipulated link or submits a form, the browser carries out the injected script within the page’s context.

The cybercriminal usually tricks the victim into clicking the manipulated link containing the malicious payload by using urgent calls to action such as “click now” or “scan now.” This type of XSS doesn’t store the payload on the target server; it’s only reflected back to users who interact with the malicious link or input.

Persistent XSS

Persistent XSS is when a cybercriminal injects malicious scripts into a web page’s database, which then gets stored on the server. The malicious payload becomes a permanent part of the web page’s content. When other users access a page that displays the stored content, the browser executes the injected script, leading to a potential compromise. This type of XSS is more dangerous than reflected XSS because the malicious payload remains active for an extended period of time, affecting all users who view the compromised content.

DOM-based XSS

DOM-based XSS happens when the malicious script modifies the Document Object Model (DOM) of a web page directly. DOM is the programming interface used by web browsers to represent and interact with the structure, content and style of web pages. The cybercriminal manipulates the page’s existing content, often by modifying JavaScript variables or elements on the page.

This type of XSS doesn’t necessarily involve server-side vulnerabilities, but instead,manipulates how the client-side code behaves. DOM-based XSS can be trickier to identify and mitigate because it often requires a deep understanding of how the specific web application processes user inputs and handles dynamic content.

The Dangers of Cross-Site Scripting

There are many dangers associated with cross-site scripting including turning trusted websites into malicious ones, data theft, session hijacking and malware infections. 

Trusted websites can turn into malicious ones

Cross-site scripting attacks can make seemingly safe and reputable websites become vehicles for delivering malicious scripts. By injecting these scripts into websites, cybercriminals can manipulate the content displayed to users, leading them to engage with harmful actions that can result in their data getting stolen.

Data theft

One of the biggest dangers of cross-site scripting attacks is the potential for cybercriminals to steal sensitive user data like personal information, login credentials and financial details. Malicious scripts used in cross-site scripting attacks can capture this data as users unknowingly interact with a compromised web page.

Session hijacking

Cross-site scripting attacks can also be used to steal a user’s session cookie, which is a small piece of data that a website sends to a browser during a user’s visit. This cookie is used to maintain and manage a user’s session on a website so they can perform actions and access different paths without having to constantly re-authenticate themselves. When a cybercriminal obtains a user’s session cookie, they can impersonate them and gain unauthorized access to their account, leading to compromised data. 

Malware

Cybercriminals can exploit cross-site scripting vulnerabilities to inject malware into a website’s content. Malware is malicious software that is installed by cybercriminals onto a user’s device unknowingly. Depending on the type of malware installed, malware can do different things like access your camera and microphone or even track your keystrokes. When users visit a compromised web page, malicious scripts can trigger a malware download, leading to devices becoming infected and sensitive data becoming compromised. 

How Can I Protect Myself From Cross-Site Scripting?

Here are a few ways you can protect yourself from cross-site scripting.

Use a dedicated password manager

A dedicated password manager is a tool designed to securely store and manage your passwords. Some dedicated password managers use strong encryption like zero-knowledge to protect your data. The only password you need to remember is your master password, which is used to decrypt and encrypt your stored data. Using a dedicated password manager is crucial to keeping yourself and your data safe from cross-site scripting because it minimizes the impact of browser vulnerabilities. 

If you’re currently using a browser-based password manager, you’re more susceptible to browser vulnerabilities, such as cross-site scripting, because your browser password manager frequently remains logged in and doesn’t offer the same security as a dedicated password manager. 

Enable MFA for accounts

Multi-Factor Authentication (MFA) adds an extra layer of security to your accounts by requiring one or more forms of additional authentication before granting access. MFA is important to enable because even if a cybercriminal manages to compromise your password through a cross-site scripting attack or other means, they would still need the additional authentication factor(s) to gain access to your account. 

Keep software updated

Regularly updating your software, operating system, web browser and any installed plugins or extensions in your web browser is crucial to preventing cybercriminals from exploiting them. Updates don’t only provide you with new features, they also provide your software and devices with security patches to fix known vulnerabilities that can be easily exploited by cybercriminals. 

Install security extensions

Installing security extensions like ad blockers and script blockers can help protect you against cross-site scripting attacks by mitigating the risk of malicious scripts getting injected into your browser. 

• Ad blockers: Ad blockers are software that prevents advertisements from playing on websites. Ad blockers work by identifying and blocking elements that are associated with advertisements such as images and scripts. Ad blockers can help prevent malicious advertisements that may contain harmful scripts from being displayed, including those used in cross-site scripting attacks. 
• Script blockers: Script blockers are browser extensions that allow users to control the execution of scripts on websites. With these extensions, users can whitelist trusted sources or domains and block scripts from untrusted or unknown sources. Using script blockers prevents malicious scripts from running in a user’s browser. It’s important to note that script blockers might affect the functionality of certain websites since they might also block legitimate scripts, meaning they’ll most likely affect your user experience on many websites.

Don’t click suspicious links

Be cautious when clicking on links–especially those from unknown or untrusted sources. Hover over links to view the actual URL before clicking to ensure they lead to legitimate websites. You can also use a URL checker like Google Transparency Report to ensure that the link is sending you to a safe website. 

Regularly clear your browser’s data

It’s important to clear your browser’s cache, cookies and history regularly. This helps prevent cybercriminals from accessing cached versions of compromised pages or exploiting stored session information which they can use for session hijacking.

Ensuring Your Safety Against Cross-Site Scripting Threats

Understanding cross-site scripting is crucial for knowing how to protect yourself and your data from this type of cyber threat. Ensuring your online accounts are secure is the first step in staying safe from various cyber threats. See how a dedicated password manager like Keeper Password Manager protects your data by starting a free 30-day trial today.