Programs must use the javax.net.ssl.SSLSocket class rather than the java.net.Socket class when transferring sensitive data over insecure communication channels. The class SSLSocket provides security protocols such as Secure Sockets Layer/Transport Layer Security (SSL/TLS) to ensure that the channel is not vulnerable to eavesdropping and malicious tampering.

The principal protections included in SSLSocket that are not provided by the Socket class are [API 2014]:

It is also important to use SSL for secure remote method invocation (RMI) communications because RMI depends on object serialization, and serialized data must be safeguarded in transit. Gong, Ellison, and Dageforde [Gong 2003] describe how to secure RMI communications using SSLSocket.

Note that this rule lacks any assumptions about the integrity of the data being sent down a socket. For information about ensuring data integrity, see SER02-J. Sign then seal objects before sending them outside a trust boundary.

Noncompliant Code Example

This noncompliant code example shows the use of regular sockets for a server application that fails to protect sensitive information in transit. The insecure code for the corresponding client application follows the server's code.

  
// Exception handling has been omitted for the sake of brevity
class EchoServer { 
  public static void main(String[] args) throws IOException {
    ServerSocket serverSocket = null;
    try {
      serverSocket = new ServerSocket(9999); 
      Socket socket = serverSocket.accept();
      PrintWriter out = new PrintWriter(socket.getOutputStream(), true); 
      BufferedReader in = new BufferedReader(
          new InputStreamReader(socket.getInputStream())); 
      String inputLine; 
      while ((inputLine = in.readLine()) != null) { 
        System.out.println(inputLine); 
        out.println(inputLine); 
      }
    } finally {
      if (serverSocket != null) {
        try {
          serverSocket.close();
        } catch (IOException x) {
          // Handle error
        }
      }
    }
  }
}

class EchoClient {
  public static void main(String[] args) 
                          throws UnknownHostException, IOException {
    Socket socket = null;
    try {
      socket = new Socket("localhost", 9999);
      PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
      BufferedReader in = new BufferedReader(
          new InputStreamReader(socket.getInputStream()));
      BufferedReader stdIn = new BufferedReader(
          new InputStreamReader(System.in));
      String userInput;
      while ((userInput = stdIn.readLine()) != null) {
        out.println(userInput);
        System.out.println(in.readLine());
      } 
    } finally {
      if (socket != null) {
        try {
          socket.close();
        } catch (IOException x) {
          // Handle error
        }
      }
    }
  }
}

Note that the sockets are properly closed in accordance with ERR05-J. Do not let checked exceptions escape from a finally block.

Compliant Solution

This compliant solution uses SSLSocket to protect packets using the SSL/TLS security protocols:

// Exception handling has been omitted for the sake of brevity
class EchoServer {
  public static void main(String[] args) throws IOException {
    SSLServerSocket sslServerSocket = null;
    try {
      SSLServerSocketFactory sslServerSocketFactory =
          (SSLServerSocketFactory) SSLServerSocketFactory.getDefault();
      sslServerSocket = (SSLServerSocket) sslServerSocketFactory.
                        createServerSocket(9999);
      SSLSocket sslSocket = (SSLSocket) sslServerSocket.accept();
      PrintWriter out = new PrintWriter(sslSocket.getOutputStream(),true);
      BufferedReader in = new BufferedReader(
          new InputStreamReader(sslSocket.getInputStream()));
      String inputLine;
      while ((inputLine = in.readLine()) != null) { 
        System.out.println(inputLine); 
        out.println(inputLine); 
      } 
    } finally {
      if (sslServerSocket != null) {
        try {
          sslServerSocket.close();
        } catch (IOException x) {
          // Handle error
        }
      }
    }
  }
}

class EchoClient {
  public static void main(String[] args) throws IOException {
    SSLSocket sslSocket = null;
    try {
      SSLSocketFactory sslSocketFactory =
          (SSLSocketFactory) SSLSocketFactory.getDefault();
      sslSocket = 
          (SSLSocket) sslSocketFactory.createSocket("localhost", 9999);
      PrintWriter out = new PrintWriter(sslSocket.getOutputStream(), true);
      BufferedReader in = new BufferedReader(
          new InputStreamReader(sslSocket.getInputStream()));
      BufferedReader stdIn = new BufferedReader(
          new InputStreamReader(System.in));
      String userInput;
      while ((userInput = stdIn.readLine()) != null) {
        out.println(userInput);
        System.out.println(in.readLine());
      }
    } finally {
      if (sslSocket != null) {
        try {
          sslSocket.close();
        } catch (IOException x) {
          // Handle error
        }
      }
    }
  }
}

Programs that use SSLSocket will block indefinitely if they attempt to connect to a port that is not using SSL. Similarly, a program that does not use SSLSocket will block when attempting to establish a connection through a port that does use SSL.

Note that SSLSocket does not validate host names, so providing an arbitrary host name to an SSLSocket is still vulnerable to a man-in-the-middle attack. Host names should be validated separately. The HttpsURLConnection class validates host names and is a suitable solution for secure web sockets.

Exceptions

MSC00-J-EX0: Because of the mechanisms that SSLSocket provides to ensure the secure transfer of packets, significant performance overhead may result. Regular sockets are sufficient under the following circumstances:

Risk Assessment

Use of plain sockets fails to provide any guarantee of the confidentiality and integrity of data transmitted over those sockets.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

MSC00-J

Medium

Likely

High

P6

L2

Automated Detection

The general case of automated detection appears to be infeasible because determining which specific data may be passed through the socket is not statically computable. An approach that introduces a custom API for passing sensitive data via secure sockets may be feasible. User tagging of sensitive data is a necessary requirement for such an approach.

ToolVersionCheckerDescription
Parasoft Jtest
SECURITY.WSC.USCUse the SSL-enabled version of classes when possible

Related Guidelines

MITRE CWE

CWE-311, Failure to Encrypt Sensitive Data

Bibliography

[API 2014]

Class Socket

[Gong 2003]

Section 11.3.3, "Securing RMI Communications"

[Ware 2008]