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Directory Traversal

Directory traversal, also known as path traversal, is a type of cyber attack that allows an attacker to access restricted files and directories on a server, usually with the goal of obtaining sensitive information. This vulnerability occurs when user input is not adequately validated and the attacker can manipulate it to traverse the server directory structure.

How it Works

In a directory traversal attack, the attacker attempts to exploit an input field (e.g., a file or image upload form, URL parameters, etc.) that takes a file path as input. By supplying specially crafted input, an attacker can manipulate the server into providing access to unauthorized files and directories.

For example, consider a web application that allows users to view the contents of a specific file by specifying its path through a URL parameter, such as:

In this case, an attacker could manipulate the path parameter to traverse the server’s directories, like this:

If the server doesn’t properly validate and sanitize the input, it might reveal the contents of the /etc/passwd file, which contains sensitive information about system users.

Mitigation Techniques

There are several methods to prevent directory traversal attacks:

  • Input Validation: Ensure that user input is strictly validated and sanitized. For example, one can check for the presence of special characters (e.g., ’..’, ’/’, ”), disallowing them if found.

  • Access Control: Implement proper access control mechanisms to prevent unauthorized access to files and directories. For example, use a whitelist approach to establish which files and directories the user is allowed to access.

  • Least Privilege: Practice the principle of least privilege by ensuring that an application runs with only the necessary permissions needed for its operation. This can minimize the potential impact of a directory traversal attack.

  • Use Chroot Jails: Deploy applications inside chroot jails to restrict access to a certain directory, thwarting attempts to traverse outside that directory.

By implementing these countermeasures, you can minimize the risk of directory traversal attacks and help protect your system’s critical files and directories.

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