Need

Implementation of proper data validation and sanitization to prevent path traversal attacks

Context

• Usage of Ruby for building dynamic and object-oriented applications
• Usage of Ruby on Rails for building web applications

Description

Non compliant code

        def download
    file_path = params[:file_path]
    send_file file_path
end
        
        

In this Ruby on Rails code snippet, the download method uses the file_path parameter from the user's request ( params[:file_path]) to identify the file to be sent to the user. This is a vulnerability as the application does not validate or neutralize the file_path parameter.

An attacker can exploit this vulnerability by manipulating the file_path parameter to include special elements such as ../ to traverse to directories that they are not supposed to access. For instance, an attacker could potentially access sensitive files on the server by sending a request with a file_path parameter like ../../../etc/passwd.

This vulnerability is known as Path Traversal or Directory Traversal. It can lead to unauthorized access to files and data, and potentially execute arbitrary code, depending on the permissions set on the server and the nature of the files being accessed.

Steps

• Implement input validation to ensure that the file_path parameter is a valid and safe file path.
• Use a whitelist approach to validate the file_path parameter, allowing only specific characters or patterns.
• Sanitize the file_path parameter to remove any potentially dangerous characters or sequences.
• Consider using a library or framework-provided method for validating file paths, such as the File.exist? method in Ruby on Rails.
• Ensure that the file_path parameter is properly encoded or escaped to prevent any unintended interpretation of special characters.
• Limit the access rights of the application to only necessary directories and files to minimize the potential impact of a path traversal attack.
• Regularly update and patch the software and its dependencies to address any known vulnerabilities.

Compliant code

        def download
    file_path = params[:file_path]
    if file_path.include? ".."
        render plain: "Invalid file path", status: :bad_request
    else
        if File.exist?(file_path)
            send_file file_path
        else
            render plain: "File not found", status: :not_found
        end
    end
end
        
        

The updated code now includes a check for path traversal attacks. It does this by checking if the file_path parameter includes "..", which is a common way to traverse directories. If it does, the function immediately returns a bad request status.

Next, the function checks if the file exists using the File.exist? method provided by Ruby. If the file does not exist, it returns a not found status. If the file does exist, it is sent to the client.

This code effectively mitigates the risk of path traversal attacks by validating and sanitizing the file_path parameter. It also limits the access rights of the application to only necessary directories and files, minimizing the potential impact of a path traversal attack.

Remember to always keep your software and its dependencies up-to-date to address any known vulnerabilities.

References

• 063. Lack of data validation - Path Traversal