A directory traversal attack, also known as a path traversal attack, is a method used to exploit insufficient security validation or sanitization of user-supplied input file names. The goal of this attack is to access directories and files that are stored outside the web root folder. By manipulating variables that reference files with "../" sequences and its variations, attackers can access restricted directories and execute commands outside of the web server's root directory.
In the context of an application that allows users to upload documents to a cloud-based file server, an attacker might exploit a directory traversal vulnerability to navigate to directories that contain sensitive documents. If the file upload functionality is not properly secured, an attacker could upload a file with a payload designed to perform directory traversal. This could allow access to confidential files that are otherwise protected by the application's access control mechanisms.
Reference:
OWASP Directory Traversal Cheat Sheet: OWASP Directory Traversal
Practical example from HTB Writeups like Forge and Anubis which demonstrate similar enumeration techniques leading to sensitive file disclosures.