403 Bypass Tool For Bulk Urls

by William

In this article, we will explore a scenario where a client initially required a black box penetration test of over a hundred different web applications that were supposed to only be accessible from internal IP addresses and therefore provide a 403 forbidden error. Once it was confirmed that these pages were indeed providing the correct 403 error, it was then necessary to test for 403 bypass vulnerabilities.

What is a 403 Error?

A 403 error is a response status code that indicates that the server understands the client’s request but refuses to fulfil it. The most common cause of a 403 error is that the user does not have sufficient permissions to access the requested resource. This error can also occur if the server has been configured to restrict access to a particular resource or if the resource has been removed or moved to a different location.

History of 403 Bypass Techniques

The art of bypassing 403 errors is not a new phenomenon. Since the dawn of the internet era, hackers and security researchers have been intrigued by the challenge of gaining unauthorized access. A simple search for “403 bypass github” will reveal a rich history of bypass techniques, with repositories spanning from the early 2000s to the present day.

How to perform a 403 Bypass?

Bypassing a 403 can be achieved in several ways, such as manipulating HTTP headers, exploiting vulnerabilities in the server software, or using brute force attacks to guess valid authentication credentials. It’s essential to remember that attempting to bypass a 403 error without proper authorization is illegal and can result in severe consequences. Over the years, many techniques have been shared on GitHub, signaling the ongoing interest and research in this area.

The Client’s Brief

Recently, Aardwolf Security were approached by a client who required a penetration test of over a hundred different web applications. These applications were only supposed to be accessible from internal IP addresses, and therefore, they should have provided a 403 forbidden error when accessed from external IP addresses. The client wanted to ensure that these applications were secure and that no unauthorised access could be gained through these applications.

Once the Aardwolf Security team confirmed that these pages were indeed providing the correct 403 error, they then had to test whether the 403 could be bypassed. However, publicly available tools on GitHub only allowed for individual URLs to be assessed. It was not practical to test each URL individually as there were over a hundred different web applications to test. Therefore, the Aardwolf Security team had to create a tool that would allow for a user to input a list of URLs, which would then each be tested using well-known 403 bypass methods.

Creating a 403 Bypass Tool

To solve the problem of testing over a hundred different web applications for 403 bypass vulnerabilities, Aardwolf Security created a new tool that would allow for a user to input a list of URLs. This tool would then test each URL using well-known 403 bypass methods. The tool was designed to be user-friendly and ensure many URL’s could be assessed consecutively.

The tool created by Aardwolf Security was able to identify several vulnerabilities in the client’s web applications, including a bypass of one of the client URLs that allowed for sensitive data to be accessed. The vulnerabilities were reported to the client, who was able to take the necessary steps to address them and improve their security posture.

The tool can be found on our GitHub repository here: https://github.com/aardwolfsecurityltd/bulk_403_bypass

To run the tool use:

bash 403_bypass.sh [input file]

If you want to reduce verbose output to only include 200 responses use the following:

bash 403_bypass.sh [input file] | grep 200

Real-world Implications of 403 Bypass

The real-world implications of bypassing 403 errors can be devastating for businesses. Unauthorized access can lead to data breaches, exposing sensitive customer information, and potential financial losses. Understanding the methods showcased in “403 bypass github” repositories is vital, not for exploitation but for safeguarding assets.

Detailed Insights into 403 Bypass Techniques

While the objective of bypassing a 403 Forbidden error remains consistent, the techniques employed are manifold. Some of the commonly used methods are:

Path Traversal: This technique involves manipulating the URL to access directories or files that aren’t directly linked or should be restricted.
HTTP Verb Tampering: This method checks if other HTTP methods like PUT or DELETE can be used to bypass the restriction.
Header Manipulation: Attackers often manipulate headers like X-Forwarded-For or Referer to deceive the server into thinking the request is legitimate or originating from an allowed source.
Cookie Manipulation: In some cases, manipulating or removing cookies can grant access to forbidden resources.

Case Studies of Successful 403 Bypass Attacks

Over the years, there have been several high-profile cases where attackers successfully bypassed 403 errors, leading to data breaches. While the specifics of each case vary, the aftermath often involves significant reputational and financial damage to the targeted organization. Here are a few notable instances:

Tech Giant Breach: In 2018, a renowned tech company was compromised when hackers bypassed 403 errors to gain unauthorized access to user data. This breach exposed millions of user accounts and resulted in a severe financial penalty for the company.
E-Commerce Platform Attack: A popular online shopping platform fell victim to a 403 bypass in 2019. The attackers exploited a misconfigured server to access customer transaction details.

Training and Awareness: The First Line of Defense

It’s crucial for organizations to train their development and IT teams about potential vulnerabilities. Regular training sessions, workshops, and seminars can help in building a culture of security awareness. Tools and repositories, like the ones found when searching for “403 bypass github”, can serve as practical resources for these training sessions. When teams are aware of potential threats, they are better positioned to prevent them.

Community Feedback and the Role of Ethical Hackers

The role of ethical hackers in today’s cybersecurity landscape cannot be overstated. By leveraging platforms like GitHub, they share their findings, tools, and techniques with the broader community. This collective knowledge serves as a foundation for many organizations to strengthen their security measures. Feedback from the community, especially regarding tools like Aardwolf Security’s, is invaluable. It helps in identifying gaps, refining methodologies, and developing more robust defense mechanisms.


In this scenario, Aardwolf Security was able to create a tool that allowed for the efficient testing of over a hundred different web applications for 403 bypass vulnerabilities. By identifying these vulnerabilities, the client was able to take the necessary steps to improve their security posture and protect their sensitive data.

Aardwolf security have been helping protect and secure SMEs against cybercriminals since 2015. With an exclusive focus on penetration testing from CREST qualified penetration testers, Aardwolf Security has the expertise you need to improve your cybersecurity posture and prevent you from becoming a victim of cybercrime.

Our penetration testing services can be tailored to your specific needs, and our team of experts are here to provide impartial information and advice every step of the way.

Get in touch today to speak with one of our Senior Consultants, or fill out our 5-minute online quote form for a bespoke quote today.

You may also like