· Alex · security  · 6 min read

A Deep Dive In The XST Vulnerability

What is XST, how to identify and mitigate?

What is XST, how to identify and mitigate?

The XST vulnerability

XST, which stands for Cross-Site Tracing, is a vulnerability that takes advantage of the HTTP TRACE method, allowing attackers to steal sensitive information from users. Think of it like a pickpocket who’s mastered the art of swiping your personal info without you even knowing. Now, you might be wondering how XST is related to other web vulnerabilities you’ve heard of, like Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF). Don’t worry, we’ll get into all that juicy info later in the post.

Understanding Cross-Site Tracing (XST)

Definition and background

XST, as mentioned earlier, stands for Cross-Site Tracing. It’s a type of web application vulnerability that allows attackers to get their hands on sensitive information from users. The key player in this attack is the HTTP TRACE method, which was originally designed to help with debugging purposes. The TRACE method, when used in an XST attack, enables the attacker to grab information like cookies, authentication tokens, and other sensitive data from users’ browsers. Once they’ve got this info, they can use it to impersonate the user or perform other malicious actions. Now, you might be thinking, “Why haven’t I heard of XST before?” Great question! Truth is, XST has been somewhat overshadowed by its more famous cousins, Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF). But don’t let that fool you – XST is just as dangerous and deserves our full attention.

Relationship with Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF)

Now that we know what XST is all about, let’s explore its relationship with those other web vulnerabilities you might’ve heard of - XSS and CSRF. It’s like a big, unhappy family of security risks, and understanding their connections will help us better protect our apps.

First up, let’s talk about XSS. In an XSS attack, a hacker injects malicious code into a legitimate website, usually through user input fields like search boxes or comment forms. When an unsuspecting user visits the infected site, the malicious code runs in their browser and can do things like stealing cookies, or redirecting to phishing sites. Now, how does XST tie into this? XST can be used to sidestep security controls meant to protect against XSS. In fact XST was discovered by a security researcher in 2003, in an attempt to bypass the HTTPOnly cookie flag.

Next, let’s discuss CSRF. In a CSRF attack, attackers trick users into performing actions on a website without their knowledge. For example, they might send a user a link that, when clicked, changes their email address or password on a site they’re already logged into. So, where does XST fit in? Just like with XSS, XST can serve as a gateway to a CSRF attack. By exploiting the XST vulnerability, the attacker can access sensitive information needed to forge a CSRF request.

The HTTP TRACE method

HTTP TRACE is one of the lesser-known HTTP methods, like GET, POST, and DELETE, but it’s still part of the HTTP/1.1 protocol. Its original purpose was to help developers with debugging by allowing them to retrieve a copy of the request and response messages for a particular URL. When an attacker sends an HTTP TRACE request to a vulnerable server, the server sends back the full request, including any headers and cookies that were part of the original request. If an attacker can trick a user into sending an HTTP TRACE request containing sensitive data (like authentication tokens or session cookies), they can intercept and steal that information.

How XST Exploits Work

Here’s a step-by-step breakdown of a typical XST attack:

  1. The attacker discovers an application that supports the HTTP TRACE method and has a vulnerable server.
  2. They craft a malicious link or script that sends an HTTP TRACE request to the target server.
  3. The unsuspecting user clicks on the link or visits the page containing the malicious script.
  4. The script sends the HTTP TRACE request from the user’s browser, including any sensitive data like cookies or authentication tokens.
  5. The server processes the HTTP TRACE request and sends back a response, including the sensitive data.
  6. The attacker intercepts the response and steals the sensitive data, which they can now use for further attacks or impersonation.

How to identify XST Vulnerabilities?

Tools and techniques to detect XST vulnerability

  1. Web vulnerability scanners: There are several web vulnerability scanners out there (both free and paid) that can help you identify XST vulnerabilities in your application. Some popular ones include OWASP ZAP, Burp Suite, and Acunetix. These tools can automatically scan your application and flag potential security issues, including XST.
  2. Manual testing: If you prefer a hands-on approach, you can test for XST vulnerabilities manually by sending custom HTTP TRACE requests to your application’s server. You can use tools like curl or Postman to do this. Current browsers prevent TRACE requests being made via JavaScript, however, other ways of sending TRACE requests with browsers exist, such as using Java.

How to Mitigate XST?

Disabling the HTTP TRACE method

The easiest and most effective way to prevent XST attacks is to simply disable the HTTP TRACE method on your server. Since TRACE is the main culprit in XST vulnerabilities, disabling it will close the door on potential exploits. Check your server’s documentation or configuration files for instructions on how to disable the TRACE method, and make sure to test your changes!

Employing secure coding practices

To keep your application safe from XST and other security risks, it’s crucial to follow secure coding practices. This includes validating and sanitizing user input, properly encoding output, and avoiding the use of unsafe functions or libraries. By adhering to secure coding guidelines, you’ll make it much harder for attackers to exploit your application.

Regular security testing and monitoring

Last, but definitely not least, it’s essential to regularly test and monitor your application for security vulnerabilities. This includes using web vulnerability scanners, manual testing, and security audits to identify and address potential issues. Additionally, keep an eye on your server and application logs for any suspicious activity that could indicate an attempted XST attack. By following these mitigation strategies, you’ll be well on your way to protecting your application and users from the XST vulnerability.


Let’s do a quick recap of the key points we’ve learned along the way:

  1. XST, or Cross-Site Tracing, is a web application vulnerability that allows attackers to steal sensitive information from users using the HTTP TRACE method.
  2. XST is related to XSS and CSRF, as it can serve as a stepping stone for these more complex attacks.
  3. The HTTP TRACE method is the main culprit in XST exploits and should be disabled to mitigate the risk.
  4. Identifying XST vulnerabilities in your application involves using web vulnerability scanners, manual testing, and keeping an eye out for common red flags.
  5. To protect your application from XST attacks, follow mitigation strategies like disabling HTTP TRACE, implementing CSP, employing secure coding practices, and regularly testing and monitoring your app for security vulnerabilities.

About the Author:


Application Security Engineer and Red-Teamer. Over 15 years of experience in Application Security, Software Engineering and Offensive Security. OSCE3 & OSCP Certified. CTF nerd.

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