Course

Directory traversal vulnerabilities arise from improper handling of user inputs that are incorporated into file paths by an application. By manipulating these inputs, attackers can navigate the file system to access files and directories that should be restricted. This vulnerability can be tested using various techniques, such as the "same value technique," which involves crafting paths that either should or should not return the same file, or by attempting to access system files like `/etc/passwd` on Linux.

In our exercises, this vulnerability is demonstrated through a PHP script that concatenates user-provided data to form a file path. If the application does not properly sanitize this input, an attacker can exploit the vulnerability by providing a path like `../../../../etc/passwd`, thereby accessing sensitive files. The key to preventing such attacks is to ensure rigorous validation and sanitization of file paths, along with proper error handling to avoid disclosing too much information.