Path traversal, also known as directory traversal, is a vulnerability that occurs when an application improperly restricts user input, allowing attackers to access unauthorized directories and files. This can lead to the exposure of sensitive data or system compromise.
How Path Traversal Works
Path traversal exploits occur when user-supplied input is used in a file path without proper validation or sanitization. By manipulating file path inputs, attackers can traverse the directory structure and access files outside the intended directory.
Example Scenario
Consider a web application that loads files based on a filename parameter in the URL:
http://example.com/view?file=report.pdf
The application may use this parameter to read and display the file’s contents. However, if the input is not properly validated, an attacker could manipulate the parameter to traverse directories, like so:
http://example.com/view?file=../../../../etc/passwd
In this case, the ../../../../ sequence moves up four directories from the web root, potentially accessing the /etc/passwd file on a Unix-based system, which contains user account information.
How to Find Path Traversal Vulnerabilities
- Manual Testing: Manually manipulate parameters in URLs, forms, and other input fields to include path traversal sequences (e.g.,
../,..%2f, etc.). - Automated Scanning: Use automated vulnerability scanners like Burp Suite, OWASP ZAP, or custom scripts to identify potential path traversal issues.
- Code Review: Review the codebase to identify improper handling of user input in file operations.
Example of Testing for Path Traversal
Suppose there’s an application with an endpoint that allows users to download their files:
http://example.com/download?file=profile.jpg
To test for path traversal, you could try the following inputs:
../../../../etc/passwd..\..\..\..\Windows\system32\drivers\etc\hosts..%2f..%2f..%2f..%2fetc%2fpasswd
The application’s response will indicate whether the traversal was successful. If the application returns sensitive data or unexpected content, it may be vulnerable to path traversal.
Mitigation
- Input Validation: Ensure all user inputs are validated and sanitized.
- Whitelist Files: Only allow access to specific directories or files.
- Use Secure Functions: Use functions that prevent directory traversal, such as those that work with absolute paths or virtual file systems.
- Least Privilege: Limit the application’s permissions to access only necessary files and directories.
Path traversal vulnerabilities can be critical, especially when they expose sensitive system files or configurations. It’s essential to test thoroughly and implement strong input validation and access controls to mitigate this risk.