Secure and restricted access to user-specific files
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.
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.