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Insecurely generated token - Validation

Need​

Secure token generation and validation

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance
  • Usage of java.io.IOException for handling input/output errors in Java
  • Usage of javax.servlet.ServletException for handling servlet exceptions
  • Usage of javax.servlet.http.HttpServlet for handling HTTP requests in Java Servlets
  • Usage of javax.servlet.http.HttpServletRequest for handling HTTP requests in Java Servlets
  • Usage of HttpServletResponse for handling HTTP responses in Java Servlets
  • Usage of io.jsonwebtoken.Jwts for JSON Web Token (JWT) generation and verification
  • Usage of SignatureAlgorithm from io.jsonwebtoken for JWT token signing and verification
  • Usage of io.jsonwebtoken.security.Keys for managing cryptographic keys in JSON Web Tokens (JWTs)

Description​

Non compliant code​

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.security.Keys;

public class UserCreationServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        // Create a token without validating the header
        String jws = Jwts.builder().setSubject(username).signWith(Keys.hmacShaKeyFor("secret".getBytes()), SignatureAlgorithm.HS256).compact();

        // TODO: Save the user and the token in the database
    }
}

The above code represents a servlet class in a Java-based backend application that handles user creation. The doPost method is meant to handle POST requests for creating a new user. The username and password are retrieved from the request parameters.

The vulnerability lies in the way the JWT (JSON Web Token) is created. The token is signed using the HS256 algorithm and a secret key, but it does not validate the header of the token. This means that an attacker could modify the header defining the algorithm with which the token is encrypted. As a result, the token may not be signed, which could lead to security issues.

In particular, an attacker could manipulate the token to use the 'none' algorithm, which means that the token would be accepted without signature verification. This could allow the attacker to impersonate any user, leading to unauthorized access and potential data breaches.

Moreover, the secret key used for signing the token is hardcoded as a string in the code, which is another security vulnerability. The key should be securely stored and not exposed in the code.

Steps​

  • Implement proper validation of the token header to ensure it is not modified.
  • Use a secure and random secret key for signing the token instead of a hardcoded value.
  • Consider using a stronger encryption algorithm for signing the token.
  • Store the user and the token securely in the database, ensuring proper access controls and encryption.

Compliant code​

import java.io.IOException;
import javax.crypto.SecretKey;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.security.Keys;

public class UserCreationServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final SecretKey key = Keys.secretKeyFor(SignatureAlgorithm.HS512); // Use a stronger encryption algorithm

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        // Create a token with proper validation of the header
        String jws = Jwts.builder().setHeaderParam("typ", "JWT").setSubject(username).signWith(key).compact();

        // TODO: Save the user and the token in the database securely with proper access controls and encryption
    }
}

The updated code now includes a secure and random secret key for signing the token, which is generated using the Keys.secretKeyFor() method from the io.jsonwebtoken.security.Keys class. This key is used to sign the token with a stronger encryption algorithm (HS512) instead of the previously used HS256.

The token is now created with proper validation of the header. The setHeaderParam("typ", "JWT") method is used to set the type of the token to JWT, ensuring that the header is not modified.

The user and the token should be saved in the database securely. This is indicated by the TODO comment. The implementation of this part depends on the specific database technology used and is beyond the scope of this code snippet. However, it is important to ensure proper access controls and encryption when storing the user and the token in the database.

References​

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