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Insecure authentication method - NTLM

Need​

Secure authentication method implementation

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance
  • Usage of javax.servlet-api for developing Java web applications with Servlets
  • Usage of commons-codec for encoding and decoding data

Description​

Non compliant code​

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class NTLMAuthenticationServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        
        String authHeader = request.getHeader("Authorization");
        if (authHeader != null) { 
            String authToken = authHeader.substring(authHeader.indexOf(" ") + 1);
            byte[] bytes = Base64.decode(authToken);
            // Here the bytes would be used to perform the NTLM authentication
            // This is a simplified representation and might not compile
        } else { 
            response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
            response.setHeader("WWW-Authenticate", "NTLM");
            response.flushBuffer();
        }
    }
}

This Java servlet demonstrates the usage of the insecure NTLM authentication method. In the doGet method, it checks if the HTTP request contains the "Authorization" header. If the header is present, it extracts the NTLM token, decodes it from Base64 and presumably uses it to authenticate the user.

However, if the "Authorization" header is not present in the request, it responds to the client with a 401 Unauthorized status and includes the "WWW-Authenticate: NTLM" header in the response. This prompts the client to send another request, this time including the "Authorization" header with the NTLM token.

The vulnerability here lies in the usage of the NTLM authentication protocol. NTLM is known to be susceptible to various security flaws, including Relay attacks where an attacker can intercept the NTLM messages during the authentication process and use them to impersonate the user. Similarly, Man-in-the-Middle attacks can be performed where the attacker intercepts and potentially modifies the communication between the client and server. Furthermore, NTLM does not provide protection against brute force attacks, where an attacker systematically tries all possible passwords until the correct one is found.

Steps​

  • Replace the use of the Legacy NTLM authentication protocol with a more secure authentication method, such as OAuth or JWT.
  • Implement strong encryption and hashing algorithms to protect sensitive data during authentication.
  • Use secure communication protocols, such as HTTPS, to prevent Man-in-the-Middle attacks.
  • Implement proper input validation and sanitization to prevent injection attacks.
  • Implement rate limiting and account lockout mechanisms to prevent brute force attacks.
  • Regularly update and patch the authentication system to address any known vulnerabilities.
  • Implement multi-factor authentication to add an extra layer of security.

Compliant code​

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import com.auth0.jwt.JWT;
import com.auth0.jwt.algorithms.Algorithm;

public class JWTAuthenticationServlet extends HttpServlet {

    private static final String SECRET = "your-secret-key";

    public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        
        String authHeader = request.getHeader("Authorization");
        if (authHeader != null) { 
            String authToken = authHeader.substring(authHeader.indexOf(" ") + 1);
            try {
                JWT.require(Algorithm.HMAC256(SECRET))
                    .build()
                    .verify(authToken);
            } catch (Exception e) {
                response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
                response.setHeader("WWW-Authenticate", "Bearer realm=\\"example\\"");
                response.flushBuffer();
                return;
            }
        } else { 
            response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
            response.setHeader("WWW-Authenticate", "Bearer realm=\\"example\\"");
            response.flushBuffer();
        }
    }
}

The above code replaces the insecure NTLM authentication method with JWT (JSON Web Tokens). JWT is a more secure method of authentication and is widely used in modern web applications.

In the doGet method, the Authorization header is retrieved from the request. If the header is not null, the JWT token is extracted from it. The token is then verified using the JWT.require method, which throws an exception if the verification fails. If the token verification fails, the server responds with a 401 Unauthorized status and a WWW-Authenticate header, prompting the client to authenticate.

The SECRET constant is used to sign the JWT tokens. This should be a strong, unique value that is kept secret.

This code assumes the use of the com.auth0:java-jwt library for handling JWTs. You can add it to your project using Maven or Gradle.

Please note that this is a simplified example and might not cover all security aspects. For example, it does not implement rate limiting, account lockout mechanisms, or multi-factor authentication. These should be implemented as well to prevent brute force attacks and add an extra layer of security.

References​

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