Exploiting and Securing File Upload Traverser Vulnerabilities: A Practical Guide
In this, my third blog, I delve into the File Upload Traverser vulnerability, a critical issue I encountered during my journey in web security. My first experience exploiting this vulnerability using Burp Suite was eye-opening, highlighting the importance of proper file path validation. This exploration has deepened my passion for ethical hacking and reinforced the need for robust security measures in web applications.
What is File Upload Traverser?
The File Upload Traverser vulnerability is a type of file upload vulnerability where an attacker exploits improper handling of file paths during the file upload process to perform directory traversal. This allows the attacker to upload files to arbitrary directories on the server by manipulating the file path using traversal sequences like ../ (dot-dot-slash). The vulnerability typically arises due to insufficient validation or sanitization of user-provided file paths.
This vulnerability can occur on any server or web application that allows users to upload files and fails to properly handle file path inputs. The type of server doesn’t matter as much as how the server-side application processes and stores uploaded files.
Impact
The File Upload Traverser vulnerability allows attackers to manipulate file paths during the upload process, often by using directory traversal sequences like ../, to place files in unauthorized directories on the server. This can lead to significant security risks, including remote code execution (RCE) if attackers upload malicious scripts, enabling them to execute arbitrary commands. It may also lead to file overwriting, where critical system or configuration files are replaced, causing service disruptions or privilege escalation. Additionally, attackers can upload webshells for persistent access or steal sensitive information by placing files into directories containing confidential data. This makes it a highly dangerous vulnerability that can compromise both server integrity and data security.
Practical Steps to Exploit
Step 1: Upload a file to the server and capture the request in Burp Suite.
Step 2: Verify the file upload location, for example, now file uploaded into “assets/upload_folder/uploads/hello.txt”.
Step 3: Upload the file again, but this time change the filename to “../../../hello.txt” to perform a directory traversal. The file will be uploaded to a different directory.
Automated Tools to Find This Vulnerability :
Burp Suite Extension: Use the File Upload Traverser extension to automatically test for this vulnerability during file uploads.
Solution
To prevent File Upload Traverser vulnerabilities, ensure proper validation and sanitization of file paths, blocking directory traversal sequences like ../. Store uploaded files in non-executable directories to prevent code execution. Restrict allowed file types using a whitelist and rename uploaded files to avoid path manipulation. Implement permission-based controls to prevent unauthorized file access. Finally, validate the content of uploaded files to ensure they don’t contain malicious code.
