How I Uncovered a High-Severity Vulnerability Using a Single HTTP Header

3 days ago 12

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How I Uncovered a High-Severity Vulnerability Using a Single HTTP Header 🚀

In the world of cybersecurity, sometimes the simplest tweaks can unveil the most significant vulnerabilities. This is the story of how a single HTTP header manipulation led me to discover a high-severity flaw in a major platform's web application. Whether you're a seasoned bug bounty hunter or just starting your journey, I hope this write-up provides insights and inspires you to think outside the box.

It all started with a routine bug bounty reconnaissance on a well-known e-commerce platform. I won't disclose the name due to responsible disclosure policies, but it's a platform many of us have interacted with.

My first step was to gather as much publicly available information as possible. Using tools like Google Dorking, I searched for exposed admin panels, configuration files, and other sensitive endpoints.

One particular find caught my attention: the robots.txt file. This file is used by websites to instruct search engine crawlers which parts of the site to ignore. However, it can also inadvertently reveal directories that the site owners might prefer to keep hidden.

Disallowed Directories Found:

User-agent: *
Disallow: /includes/
Disallow: /app/
Disallow: /admin/
Disallow: /secure/
Disallow: /sys/
Disallow: /api/
Disallow: /config/

Curiosity piqued, I began probing these directories.

Access Denied... Or Is It?

Most of the disallowed directories returned a 403 Forbidden response. However, the /sys/ directory behaved differently. Initially, it returned a 200 OK response with limited content. After a while, it switched back to 403 Forbidden.

Thinking Outside the Box

I suspected that the server was performing IP-based access control, perhaps only allowing requests from specific IP addresses or localhost (127.0.0.1). This led me to test whether the server trusted the X-Forwarded-For HTTP header, which is often used to identify the originating IP address of a client connecting through a proxy.

The Game-Changing Request:

GET /sys/ HTTP/1.1
Host: targetwebsite.com
X-Forwarded-For: 127.0.0.1

To my excitement, the server responded with 200 OK, and the response body contained internal HTML content!

Information Disclosure

The HTML content revealed several internal details:

Server Technologies:

Meta tags indicating the use of Microsoft Visual Studio .NET and Visual Basic .NET.

Hidden Input Fields:

__VIEWSTATE and __VIEWSTATEGENERATOR, suggesting the use of ASP.NET Web Forms.

Session Identifiers:

An ASP.NET_SessionId cookie was set, which could potentially be used in session fixation attacks.

Encouraged by these findings, I decided to test other HTTP methods and see how the server would react.

Testing HEAD, POST, and PUT Requests:

Sending these requests without a Content-Length header resulted in a 411 Length Required response.

Adding Content-Length: 0 allowed the POST and PUT requests to succeed.

POST /sys/ HTTP/1.1
Host: targetwebsite.com
X-Forwarded-For: 127.0.0.1
Content-Length: 0

At this point, I had:

Bypassed IP-based Access Controls: By spoofing the X-Forwarded-For header.

Discovered Sensitive Information: About the server's technologies and configurations.

Identified HTTP Method Vulnerabilities: The server accepted POST and PUT requests, potentially allowing for further exploitation.

Unauthorized Access: Attackers could access restricted directories and files.

Information Disclosure: Knowledge of server technologies aids in crafting targeted attacks.

Data Manipulation: With PUT requests accepted, there might be a risk of unauthorized file uploads or modifications.

Session Hijacking: Exposed session IDs increase the risk of session fixation or hijacking attacks.

Understanding the severity, I compiled a detailed report and submitted it to the company's security team under their responsible disclosure program. They acknowledged the vulnerability and rewarded me accordingly.

1. Never Underestimate Simple Methods:

Sometimes, basic techniques like header manipulation can yield significant results.

2. Thorough Reconnaissance is Crucial:

Always analyze robots.txt and other publicly accessible files for hidden gems.

3. Test Various HTTP Methods:

Don't limit yourself to GET requests; exploring other methods can uncover additional vulnerabilities.

4. Understand HTTP Responses:

Pay attention to response codes like 411 Length Required and adjust your approach accordingly.

5. Stay Ethical and Responsible:

Always follow responsible disclosure policies to help make the internet a safer place.

This experience reinforced my belief in the power of curiosity and persistence in cybersecurity. As ethical hackers and security enthusiasts, we have the responsibility to use our skills for good.

If you're venturing into bug bounty hunting or cybersecurity:

Stay Curious: Always ask questions and explore the "what ifs."

Keep Learning: The field is ever-evolving; continuous learning is key.

Share Knowledge: Educate others and contribute to the community.

Let's work together to build a safer digital world! 🌐

Join the Conversation 💬

Have you had similar experiences or discoveries? Share your thoughts or stories in the comments below!

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