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Insecure object reference - Files

Need​

Secure and restricted access to user-specific files

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance
  • Usage of javax.servlet-api for Java Servlet development

Description​

Non compliant code​

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class FileServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) {
        String fileID = request.getParameter("fileID");
        File file = FileDAO.getFile(fileID);
        response.setContentType("application/octet-stream");
        response.setHeader("Content-Disposition", "attachment; filename=" + file.getName());
        response.getOutputStream().write(file.getContent());
    }
}

In the above code, we have a FileServlet class which extends HttpServlet. This servlet handles GET requests and serves files to the user.

The doGet() method retrieves the file ID from the request parameters and uses this ID to fetch the corresponding file from the database through the FileDAO.getFile(fileID) method.

The problem lies in the fact that there is no validation check to see if the user requesting the file has the necessary permissions to access it. This means that if an unauthorized user somehow learns the ID of a file, they can easily access or manipulate the file just by sending a GET request with the file ID.

This is an example of an Insecure Direct Object Reference (IDOR) vulnerability, where an application exposes an internal implementation object, such as a file or database key. Without an access control check or other protection, attackers can manipulate these references to access unauthorized data.

Steps​

  • Implement proper authentication and authorization mechanisms to ensure that only authorized users can access and manipulate files.
  • Validate the user's permissions before allowing access to a file. This can be done by checking if the user has the necessary privileges to access the requested file.
  • Avoid using direct object references as identifiers for files. Instead, use a secure and unique identifier that cannot be easily guessed or manipulated by unauthorized users.
  • Implement access control checks at the server-side to ensure that the user has the necessary permissions to perform the requested action on the file.
  • Consider implementing a file access control list (ACL) to manage and enforce fine-grained access control for files.
  • Encrypt sensitive information in the file, such as user data or confidential data, to protect it from unauthorized access even if the file is accessed by an authorized user.
  • Regularly update and patch the application to address any security vulnerabilities that may arise.
  • Conduct regular security audits and penetration testing to identify and address any potential vulnerabilities in the file management system.

Compliant code​

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class FileServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) {
        String fileID = request.getParameter("fileID");
        User user = (User) request.getSession().getAttribute("authenticatedUser");
        
        if(user == null) {
            response.sendError(HttpServletResponse.SC_UNAUTHORIZED);
            return;
        }
        
        File file = FileDAO.getFile(fileID);
        
        if(file == null || !file.getOwner().equals(user)) {
            response.sendError(HttpServletResponse.SC_FORBIDDEN);
            return;
        }
        
        response.setContentType("application/octet-stream");
        response.setHeader("Content-Disposition", "attachment; filename=" + file.getName());
        response.getOutputStream().write(file.getContent());
    }
}

The updated code now includes an authentication and authorization check before allowing access to a file.

Firstly, it retrieves the authenticated user from the session. If no user is authenticated, it sends an HTTP 401 Unauthorized error and returns.

Next, it retrieves the file using the provided file ID. If the file does not exist or the authenticated user is not the owner of the file, it sends an HTTP 403 Forbidden error and returns.

Only if the user is authenticated and has the necessary permissions, the file is sent to the user.

This way, we ensure that only authorized users can access and manipulate files, and we validate the user's permissions before allowing access to a file.

Please note that this is a basic example and real-world applications would require more complex access control mechanisms, such as role-based access control (RBAC) or access control lists (ACLs).

Also, sensitive information in the file should be encrypted to protect it from unauthorized access, and the application should be regularly updated and audited for security vulnerabilities.

References​

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