This rule enforces the secure verification of SSL/TLS hostnames when validating certificates. In secure communication, this step is crucial to prevent Man-In-The-Middle (MITM) attacks. In such a case, an attacker could intercept the communication, present a fraudulent certificate, and if hostname verification is not implemented or is improperly implemented, the client might accept it.
Developers sometimes disable hostname verification for testing purposes or to bypass certain network restrictions. This practice opens up a serious security vulnerability when used in production code. You must ensure that you do not override the hostname verifier to return true for all hostnames, because this accepts any certificate, even if it’s not valid for the server you’re connecting to.
To avoid violating this rule, always use the default hostname verification provided by the SSL/TLS library (such as OkHttpClient, HttpsURLConnection, or SSLContext). These libraries have secure hostname verification enabled by default; do not disable or modify it. If you need to handle exceptions for certain hostnames, you can use a custom hostname verifier that checks the hostname against a list of allowed exceptions instead of accepting all hostnames.