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 2006]:
- Integrity Protection: SSL protects against modification of messages by an active wiretapper.
- Authentication: In most modes, SSL provides peer authentication. Servers are usually authenticated, and clients may be authenticated as requested by servers.
- Confidentiality (privacy protection): In most modes, SSL encrypts data being sent between client and server. This protects the confidentiality of data so that passive wiretappers cannot observe sensitive data such as financial or personal information.
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 rule SER02-J. Sign then seal sensitive 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 rule 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.
Exceptions
MSC00-EX0: Because of the mechanisms that SSLSocket provides to ensure the secure transfer of packets, significant performance overhead may result. Regular sockets are sufficient when
- the data being sent over the socket is not sensitive.
- the data is sensitive, but properly encrypted. See rule SER02-J. Sign then seal sensitive objects before sending them outside a trust boundary for more information.
- the network path of the socket never crosses a trust boundary. This could happen when, for example, the two endpoints of the socket are within the same local network and the entire network is trusted.
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.