403 Forbidden Error: Access Control Bug Hunting

As a security researcher or bug hunter, one of the most common error codes you will encounter while testing web applications is the 403 Forbidden status code. This error indicates that the server understands the request, but refuses to authorize it due to lack of proper authentication or permission.

This article is discussing about 403 Forbidden error which is a HTTP status code that is returned by a web server when a client, such as a web browser, attempts to access a resource on the server but is not authorized to do so. The article discussed that this error can occur for a variety of reasons, such as a lack of proper authentication, a lack of proper access control, or a misconfigured web server. The article provided details on how to identify and report 403 errors as security issues and made it clear that, properly identifying and reporting 403 errors can help ensure that applications are secure and protect sensitive data from unauthorized access. The article also highlights the importance of security researchers or bug hunters in identifying this kind of errors and how to mitigate them.

What is a 403 forbidden error?

A 403 Forbidden error is a HTTP status code that is returned by a web server when a client, such as a web browser, attempts to access a resource on the server but is not authorized to do so. This can happen for a variety of reasons, such as a lack of proper authentication, a lack of proper access control, or a misconfigured web server. When a 403 error occurs, the server will typically return a message indicating that the request was understood, but the server is refusing to authorize it due to lack of proper authorization or permission. This error can indicate a potential security vulnerability in the application and should be investigated further by a security researcher or bug hunter.

When a 403 error occurs, it is important to understand the root cause and determine if it is a potential security vulnerability. In this article, we will explore some common causes of 403 errors and how to identify and report them as security issues.

One common cause of 403 errors is a lack of proper authentication. If an application is not properly verifying user credentials, an attacker may be able to bypass authentication and gain unauthorized access to sensitive data. To identify this type of vulnerability, a researcher can attempt to access protected resources without proper credentials or try to manipulate the authentication process to gain access.

Another common cause of 403 errors is a lack of proper access control. This occurs when an application does not properly restrict access to sensitive resources based on a user’s role or permissions. An attacker can exploit this type of vulnerability by manipulating the access control mechanisms to gain access to resources they should not have access to.

A third common cause of 403 errors is a misconfigured web server. This can happen when the server is not properly configured to handle certain types of requests or is configured to block certain types of access. A researcher can identify this type of vulnerability by attempting to access resources that should be accessible and observing the server’s behavior.

Request / Response Manual Manipulation →

Convert your GET request to a POST request:

GET /admin HTTP/1.1
Host: website.com

Modified:

POST /admin HTTP/1.1
Host: website.com

Appending %2e (URL encoded ‘.’) to possibly show directory traversal through the URL:

http://website.com/admin

Modified:

http://website.com/%2e/admin

Taking it further:

http://website.com/admin/.
http://website.com//admin//
http://website.com/./admin/..
http://website.com/;/admin
http://website.com/.;/admin
http://website.com//;//admin

Modifying cases in the URL path:

http://website.com/admin

Modified:

http://website.com/aDmIN

Automation Bypass Tools →

One tool I found that’s really helpful for speeding this checking process up is Bypass-403 on Github (who could have guessed a tool like this would be included in a 403 bypass article), and I’ve included installation and usage information here to share with others.

Installation:

~$ git clone https://github.com/iamj0ker/bypass-403 ~$ cd bypass-403~$ chmod +x bypass-403.sh

Usage:

~$ ./bypass-403.sh https://example.com admin

Essentially, it evaluates to ‘./bypass-403.sh website-here path-here’. It’s simple and utilizes 24 different bypass checks, some of which are mentioned in this post. If you’ve read my other articles on , you’ll know that I’m a big fan of automation and this script helps with exactly that.

It looks a bit old but covers the same stuff, and it still works just as well and was updated about 6 months ago (which would be June of 2022).

Importance of security researchers or bug hunters

Security researchers or bug hunters play a crucial role in identifying and mitigating security vulnerabilities in web applications. They are responsible for identifying and reporting any issues that may put sensitive data at risk, and they work closely with developers to ensure that these issues are addressed in a timely manner.

By constantly testing web applications for vulnerabilities, security researchers and bug hunters help to prevent cyber attacks and data breaches. They have the knowledge and skills to identify potential threats and know how to manipulate the system to identify flaws. They can use automated tools, manual testing, and various security techniques to discover vulnerabilities. They are also able to simulate an attacker's behavior and provide guidance on how to prevent real-world attacks.

Another importance of security researchers and bug hunters is that they work as an independent third party, they are not bound by any company policy or regulation which makes them more effective in identifying security issues. They can also act as a layer of protection for any company or application. They can help identify any hidden vulnerabilities that internal security teams may not be aware of.

Overall, security researchers and bug hunters play a vital role in maintaining the security and integrity of web applications, and their contributions are essential for protecting sensitive data from unauthorized access.

Conclusion

In conclusion, 403 Forbidden errors are a common indication of potential security vulnerabilities in web applications. As a security researcher or bug hunter, it is important to understand the root cause of these errors and determine if they represent a potential security threat. Properly identifying and reporting 403 errors can help ensure that applications are secure and protect sensitive data from unauthorized access. Whether the cause is a lack of proper authentication, a lack of proper access control, or a misconfigured web server, it is essential to thoroughly investigate and report any 403 errors that are encountered during testing. By doing so, we can help make the internet a safer place for everyone.