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Automatic information enumeration

Need​

Prevention of automatic information enumeration and unauthorized access to sensitive data

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance
  • Usage of javax.servlet for building Java web applications with Servlet technology
  • Usage of javax.servlet.http for handling HTTP requests and responses in Java servlets
  • Usage of java.io.PrintWriter for writing formatted text output to a character-output stream
  • Usage of java.io.IOException for handling input/output errors in Java programming

Description​

Non compliant code​

import javax.servlet.*;
import javax.servlet.http.*;

public class InfoEnumerationServlet extends HttpServlet {

  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    String systemInfo = "";
    systemInfo += "OS: " + System.getProperty("os.name") + "<br/>";
    systemInfo += "OS Version: " + System.getProperty("os.version") + "<br/>";
    systemInfo += "Java Version: " + System.getProperty("java.version") + "<br/>";
    systemInfo += "Java Vendor: " + System.getProperty("java.vendor") + "<br/>";
    systemInfo += "User Home Directory: " + System.getProperty("user.home") + "<br/>";
    PrintWriter out = response.getWriter();
    out.println("<html><body>" + systemInfo + "</body></html>");
  }
}

This servlet is vulnerable to automatic information enumeration. When a GET request is made to the servlet, it responds with various system information that could be useful for an attacker.

The system information includes:

  • The operating system name
  • The operating system version
  • The Java version
  • The Java vendor
  • The user's home directory

This information is gathered using the System.getProperty() method and then sent back to the client in the HTTP response.

An attacker could use this information to identify potential weaknesses in the system's configuration and the Java environment. For example, knowing the operating system and its version can help an attacker to craft specific attacks for that system. Similarly, knowing the Java version and vendor can reveal whether any known vulnerabilities exist for that specific version.

In addition, revealing the user's home directory can potentially expose sensitive user data. If an attacker gains access to the system, they would know exactly where to look for user data.

Therefore, it is critical to avoid exposing such sensitive information to prevent potential attacks.

Steps​

  • Avoid exposing sensitive system information in the response.
  • Remove the code that retrieves and concatenates system information.
  • Consider implementing access controls to restrict who can access the servlet.
  • Regularly update and patch the server to prevent unauthorized access to system information.
  • Implement secure coding practices to prevent information leakage.

Compliant code​

import javax.servlet.*;
import javax.servlet.http.*;

public class InfoEnumerationServlet extends HttpServlet {

  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    // Removed the code that retrieves and concatenates system information.
    PrintWriter out = response.getWriter();
    out.println("<html><body>" + "Access Denied" + "</body></html>");
  }
}

The original code was vulnerable to automatic information enumeration as it was exposing sensitive system information such as the operating system name, version, Java version, Java vendor, and user home directory. This information could be used by an attacker to gain unauthorized access to the system or to launch further attacks.

The fixed code removes the retrieval and concatenation of system information. Instead, it simply responds with "Access Denied". This prevents any system information from being exposed to the client.

In addition to this code fix, it is recommended to implement access controls to restrict who can access the servlet. This could be done through authentication and authorization mechanisms. Regularly updating and patching the server can also help prevent unauthorized access to system information.

Finally, it is important to follow secure coding practices to prevent information leakage. This includes validating and sanitizing input, encrypting sensitive data, and using secure communication protocols.

References​

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