To establish a SSL/TLS connection not vulnerable to man-in-the-middle attacks, it's essential to make sure the server presents the right certificate.
The certificate's hostname-specific data should match the server hostname.

It's not recommended to re-invent the wheel by implementing custom hostname verification.
TLS/SSL libraries provide built-in hostname verification functions that should be used.

This rule raises an issue when:

* ``++HostnameVerifier.verify()++`` method always ``++return true++``
* a JavaMail's ``++javax.mail.Session++`` is created with a ``++Properties++`` object having no ``++mail.smtp.ssl.checkserveridentity++`` or ``++mail.smtps.ssl.checkserveridentity++`` not configured to ``++true++``
* a Apache Common Emails's ``++org.apache.commons.mail.SimpleEmail++`` is used with ``++setSSLOnConnect(true)++`` or ``++setStartTLSEnabled(true)++`` or ``++setStartTLSRequired(true)++`` without a call to ``++setSSLCheckServerIdentity(true)++``

== Noncompliant Code Example

----
URL url = new URL("https://example.org/");
HttpsURLConnection urlConnection = (HttpsURLConnection)url.openConnection();
urlConnection.setHostnameVerifier(new HostnameVerifier() {
  @Override
  public boolean verify(String requestedHost, SSLSession remoteServerSession) {
    return true;  // Noncompliant
  }
});
InputStream in = urlConnection.getInputStream();

----

SimpleEmail example:

----
Email email = new SimpleEmail();
email.setSmtpPort(465);
email.setAuthenticator(new DefaultAuthenticator(username, password));
email.setSSLOnConnect(true); // Noncompliant; setSSLCheckServerIdentity(true) should also be called before sending the email
email.send();
----

JavaMail's example:

----
Properties props = new Properties();
props.put("mail.smtp.host", "smtp.gmail.com");
props.put("mail.smtp.socketFactory.port", "465");
props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory"); // Noncompliant; Session is created without having "mail.smtp.ssl.checkserveridentity" set to true
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.port", "465");
Session session = Session.getDefaultInstance(props, new javax.mail.Authenticator() {
  protected PasswordAuthentication getPasswordAuthentication() {
    return new PasswordAuthentication("username@gmail.com", "password");
  }
});
----

== Compliant Solution

----
URL url = new URL("https://example.org/");
HttpsURLConnection urlConnection = (HttpsURLConnection)url.openConnection();
// Compliant; Use the default HostnameVerifier
InputStream in = urlConnection.getInputStream();
----

SimpleEmail example:

----
Email email = new SimpleEmail();
email.setSmtpPort(465);
email.setAuthenticator(new DefaultAuthenticator(username, password));
email.setSSLOnConnect(true);
email.setSSLCheckServerIdentity(true); // Compliant
email.send();
----

JavaMail's example:

----
Properties props = new Properties();
props.put("mail.smtp.host", "smtp.gmail.com");
props.put("mail.smtp.socketFactory.port", "465");
props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.port", "465");
props.put("mail.smtp.ssl.checkserveridentity", true); // Compliant
Session session = Session.getDefaultInstance(props, new javax.mail.Authenticator() {
  protected PasswordAuthentication getPasswordAuthentication() {
    return new PasswordAuthentication("username@gmail.com", "password");
  }
});
----

== See

* https://www.owasp.org/index.php/Top_10-2017_A6-Security_Misconfiguration[OWASP Top 10 2017 Category A6] - Security Misconfiguration
* http://cwe.mitre.org/data/definitions/295.html[MITRE, CWE-295] - Improper Certificate Validation
* Derived from FindSecBugs rule https://find-sec-bugs.github.io/bugs.htm#WEAK_HOSTNAME_VERIFIER[WEAK_HOSTNAME_VERIFIER]