(#) Insecure `HostnameVerifier` !!! WARNING: Insecure `HostnameVerifier` This is a warning. Id : `AllowAllHostnameVerifier` Summary : Insecure `HostnameVerifier` Severity : Warning Category : Security Platform : Android Vendor : Android Open Source Project Feedback : https://issuetracker.google.com/issues/new?component=192708 Since : 1.5.0 (November 2015) Affects : Kotlin and Java files Editing : This check runs on the fly in the IDE editor See : https://goo.gle/AllowAllHostnameVerifier Implementation : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/AllowAllHostnameVerifierDetector.java) Tests : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AllowAllHostnameVerifierDetectorTest.java) This check looks for use of HostnameVerifier implementations whose `verify` method always returns true (thus trusting any hostname) which could result in insecure network traffic caused by trusting arbitrary hostnames in TLS/SSL certificates presented by peers. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test/pkg/InsecureHostnameVerifier.java:22:Warning: Using the AllowAllHostnameVerifier HostnameVerifier is unsafe because it always returns true, which could cause insecure network traffic due to trusting TLS/SSL server certificates for wrong hostnames [AllowAllHostnameVerifier] connection.setHostnameVerifier(new AllowAllHostnameVerifier()); ------------------------------ src/test/pkg/InsecureHostnameVerifier.java:23:Warning: Using the ALLOW_ALL_HOSTNAME_VERIFIER HostnameVerifier is unsafe because it always returns true, which could cause insecure network traffic due to trusting TLS/SSL server certificates for wrong hostnames [AllowAllHostnameVerifier] connection.setHostnameVerifier(SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER); -------------------------------------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test/pkg/InsecureHostnameVerifier.java`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers package test.pkg; import android.content.Intent; import java.io.IOException; import java.net.URL; import javax.net.ssl.HostnameVerifier; import javax.net.ssl.HttpsURLConnection; import javax.net.ssl.SSLContext; import javax.net.ssl.SSLSession; import javax.net.ssl.TrustManager; import javax.net.ssl.X509TrustManager; import org.apache.http.conn.ssl.SSLSocketFactory; import org.apache.http.conn.ssl.AllowAllHostnameVerifier; public class InsecureHostnameVerifier { protected void onHandleIntent(Intent intent) { try { URL url = new URL("https://www.google.com"); HttpsURLConnection connection = (HttpsURLConnection) url.openConnection(); connection.setHostnameVerifier(new AllowAllHostnameVerifier()); connection.setHostnameVerifier(SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER); } catch (IOException e) { System.out.println(e.getStackTrace()); } } } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AllowAllHostnameVerifierDetectorTest.java) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `AllowAllHostnameVerifierDetector.testBroken`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=192708. (##) Suppressing You can suppress false positives using one of the following mechanisms: * Using a suppression annotation like this on the enclosing element: ```kt // Kotlin @Suppress("AllowAllHostnameVerifier") fun method() { setHostnameVerifier(...) } ``` or ```java // Java @SuppressWarnings("AllowAllHostnameVerifier") void method() { setHostnameVerifier(...); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection AllowAllHostnameVerifier problematicStatement() ``` * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="AllowAllHostnameVerifier" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'AllowAllHostnameVerifier' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore AllowAllHostnameVerifier ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).