This vulnerability allows attackers to impersonate a trusted host.
Why is this an issue?
Transport Layer Security (TLS) provides secure communication between systems over the internet by encrypting the data sent between them. In this
process, the role of hostname validation, combined with certificate validation, is to ensure that a system is indeed the one it claims to be, adding
an extra layer of trust and security.
When hostname validation is disabled, the client skips this critical check. This creates an opportunity for attackers to pose as a trusted entity
and intercept, manipulate, or steal the data being transmitted.
To do so, an attacker would obtain a valid certificate authenticating example.com, serve it using a different hostname, and the
application code would still accept it.
What is the potential impact?
Establishing trust in a secure way is a non-trivial task. When you disable hostname validation, you are removing a key mechanism designed to build
this trust in internet communication, opening your system up to a number of potential threats.
Identity spoofing
If a system does not validate hostnames, it cannot confirm the identity of the other party involved in the communication. An attacker can exploit
this by creating a fake server and masquerading it as a legitimate one. For example, they might set up a server that looks like your bank’s server,
tricking your system into thinking it is communicating with the bank. This scenario, called identity spoofing, allows the attacker to collect any data
your system sends to them, potentially leading to significant data breaches.
How to fix it in Apache Commons Email
Code examples
The following code contains examples of disabled hostname validation.
The hostname validation gets disabled because setSSLCheckServerIdentity is omitted. To enable validation, set it to
true.
Noncompliant code example
import org.apache.commons.mail.DefaultAuthenticator;
import org.apache.commons.mail.Email;
import org.apache.commons.mail.SimpleEmail;
public void sendMail(String message) {
Email email = new SimpleEmail();
email.setMsg(message);
email.setSmtpPort(465);
email.setAuthenticator(new DefaultAuthenticator(username, password));
email.setSSLOnConnect(true); // Noncompliant
email.send();
}
Compliant solution
import org.apache.commons.mail.DefaultAuthenticator;
import org.apache.commons.mail.Email;
import org.apache.commons.mail.SimpleEmail;
public void sendMail(String message) {
Email email = new SimpleEmail();
email.setMsg(message);
email.setSmtpPort(465);
email.setAuthenticator(new DefaultAuthenticator(username, password));
email.setSSLCheckServerIdentity(true);
email.setSSLOnConnect(true);
email.send();
}
How does this work?
To fix the vulnerability of disabled hostname validation, it is strongly recommended to first re-enable the default validation and fix the root
cause: the validity of the certificate.
Use valid certificates
If a hostname validation failure prevents connecting to the target server, keep in mind that one system’s code should not work around
another system’s problems, as this creates unnecessary dependencies and can lead to reliability issues.
Therefore, the first solution is to change the remote host’s certificate to match its identity. If the remote host is not under your control,
consider replicating its service to a server whose certificate you can change yourself.
In case the contacted host is located on a development machine, and if there is no other choice, try following this solution:
- Create a self-signed certificate for that machine.
- Add this self-signed certificate to the system’s trust store.
- If the hostname is not
localhost, add the hostname in the /etc/hosts file.
Here is a sample command to import a certificate to the Java trust store:
keytool -import -alias myserver -file myserver.crt -keystore cacerts
How to fix it in Java SE
Code examples
The following code contains examples of disabled hostname validation.
The hostname validation gets disabled by overriding javax.net.ssl.HostnameVerifier.verify() with an empty implementation. It is highly
recommended to use the original implementation.
Noncompliant code example
import java.io.InputStream;
import java.net.URL;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLSession;
import javax.net.ssl.HostnameVerifier;
public InputStream doRequest() {
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
}
});
return urlConnection.getInputStream();
}
Compliant solution
import java.io.InputStream;
import java.net.URL;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLSession;
public InputStream doRequest() {
URL url = new URL("https://example.org/");
HttpsURLConnection urlConnection = (HttpsURLConnection)url.openConnection();
return urlConnection.getInputStream();
}
How does this work?
To fix the vulnerability of disabled hostname validation, it is strongly recommended to first re-enable the default validation and fix the root
cause: the validity of the certificate.
Use valid certificates
If a hostname validation failure prevents connecting to the target server, keep in mind that one system’s code should not work around
another system’s problems, as this creates unnecessary dependencies and can lead to reliability issues.
Therefore, the first solution is to change the remote host’s certificate to match its identity. If the remote host is not under your control,
consider replicating its service to a server whose certificate you can change yourself.
In case the contacted host is located on a development machine, and if there is no other choice, try following this solution:
- Create a self-signed certificate for that machine.
- Add this self-signed certificate to the system’s trust store.
- If the hostname is not
localhost, add the hostname in the /etc/hosts file.
Here is a sample command to import a certificate to the Java trust store:
keytool -import -alias myserver -file myserver.crt -keystore cacerts
How to fix it in Java EE
Code examples
The following code contains examples of disabled hostname validation.
The hostname validation gets disabled because mail.smtp.ssl.checkserveridentity is omitted. To enable validation, set it to
true.
Noncompliant code example
import java.util.Properties;
public Properties prepareEmailConnection() {
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
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.port", "465");
return props;
}
Compliant solution
import java.util.Properties;
public Properties prepareEmailConnection() {
Properties props = new Properties();
props.put("mail.smtp.host", "smtp.gmail.com");
props.put("mail.smtp.socketFactory.port", "465");
props.put("mail.smtp.ssl.checkserveridentity", true);
props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.port", "465");
return props;
}
How does this work?
To fix the vulnerability of disabled hostname validation, it is strongly recommended to first re-enable the default validation and fix the root
cause: the validity of the certificate.
Use valid certificates
If a hostname validation failure prevents connecting to the target server, keep in mind that one system’s code should not work around
another system’s problems, as this creates unnecessary dependencies and can lead to reliability issues.
Therefore, the first solution is to change the remote host’s certificate to match its identity. If the remote host is not under your control,
consider replicating its service to a server whose certificate you can change yourself.
In case the contacted host is located on a development machine, and if there is no other choice, try following this solution:
- Create a self-signed certificate for that machine.
- Add this self-signed certificate to the system’s trust store.
- If the hostname is not
localhost, add the hostname in the /etc/hosts file.
Here is a sample command to import a certificate to the Java trust store:
keytool -import -alias myserver -file myserver.crt -keystore cacerts
Resources
Standards
