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CVE-2021-41773

cve-2021 | Level: Easy  | Total Lab Runs: 0 | Premium Lab

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The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems including UNIX and Windows. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards.  

In mid 2021, a flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions.  

This issue has been assigned a CVE identifier of CVE-2021-41773.  

In this lab environment, the user is going to get access to a Kali GUI instance. An Apache web server vulnerable to CVE-2021-41773 is accessible from the tools installed on the Kali machine at http://demo.ine.local.  

Objective: Exploit the path traversal vulnerability in the Apache web server to retrieve the system files and also retrieve the flag from the file /tmp/flag.txt.

Acknowledgements:

The setup code is based on the following Github repository: https://github.com/vulhub/vulhub/tree/master/httpd/CVE-2021-41773

Instructions:

  • This lab is dedicated to you! No other users are on this network :) 

  • Once you start the lab, you will have access to a root terminal of a Kali instance

  • Your Kali has an interface with IP address 192.X.Y.Z. Run "ip addr" to know the values of X and Y.

  • The target server should be located at the IP address 192.X.Y.3. It can be accessed using the hostname demo.ine.local

  • Do not attack the gateway located at IP address 192.X.Y.1

The following activities are strictly prohibited on this website unless otherwise explicitly stated as allowed in the mission statement:

  • Using automated scanners
  • Using brute force attacks
  • Denial of Service attacks
  • Attacking other student machines in challenges where you might achieve a shell on the vulnerable system
  • Attacking the lab infrastructure

Users violating the above will be either temporarily or permanently banned from the website. 

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