WebView: how to avoid security alert from Google Play upon implementation of onReceivedSslError

Question

I have a link which will open in WebView. The problem is it cannot be open until I override onReceivedSslError like this:

@Override
public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
    handler.proceed();
}

I am getting security alert from Google Play saying:

Security alert Your application has an unsafe implementation of the WebViewClient.onReceivedSslError handler. Specifically, the implementation ignores all SSL certificate validation errors, making your app vulnerable to man-in-the-middle attacks. An attacker could change the affected WebView's content, read transmitted data (such as login credentials), and execute code inside the app using JavaScript.

To properly handle SSL certificate validation, change your code to invoke SslErrorHandler.proceed() whenever the certificate presented by the server meets your expectations, and invoke SslErrorHandler.cancel() otherwise. An email alert containing the affected app(s) and class(es) has been sent to your developer account address.

Please address this vulnerability as soon as possible and increment the version number of the upgraded APK. For more information about the SSL error handler, please see our documentation in the Developer Help Center. For other technical questions, you can post to https://www.stackoverflow.com/questions and use the tags “android-security” and “SslErrorHandler.” If you are using a 3rd party library that’s responsible for this, please notify the 3rd party and work with them to address the issue.

To confirm that you've upgraded correctly, upload the updated version to the Developer Console and check back after five hours. If the app hasn't been correctly upgraded, we will display a warning.

Please note, while these specific issues may not affect every app that uses WebView SSL, it's best to stay up to date on all security patches. Apps with vulnerabilities that expose users to risk of compromise may be considered dangerous products in violation of the Content Policy and section 4.4 of the Developer Distribution Agreement.

Please ensure all apps published are compliant with the Developer Distribution Agreement and Content Policy. If you have questions or concerns, please contact our support team through the Google Play Developer Help Center.

If I remove onReceivedSslError (handler.proceed()), then page won't open.

Is there any way I can open the page in WebView and avoid security alert?

Answer 1

To properly handle SSL certificate validation, change your code to invoke SslErrorHandler.proceed() whenever the certificate presented by the server meets your expectations, and invoke SslErrorHandler.cancel() otherwise.

As email said, onReceivedSslError should handle user is going to a page with invalid cert, such like a notify dialog. You should not proceed it directly.

For example, I add an alert dialog to make user have confirmed and seems Google no longer shows warning.

---

@Override
public void onReceivedSslError(WebView view, final SslErrorHandler handler, SslError error) {
    final AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setMessage(R.string.notification_error_ssl_cert_invalid);
    builder.setPositiveButton("continue", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            handler.proceed();
        }
    });
    builder.setNegativeButton("cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            handler.cancel();
        }
    });
    final AlertDialog dialog = builder.create();
    dialog.show();
}

---

More explain about the email.

Specifically, the implementation ignores all SSL certificate validation errors, making your app vulnerable to man-in-the-middle attacks.

The email says the default implement ignored an important SSL security problem. So we need to handle it in our own app which used WebView. Notify user with a alert dialog is a simple way.

Answer 2

The proposed solutions so far just bypass the security check, so they are not safe.

What I suggest is to embed the certificate(s) in the App, and when a SslError occurs, check that the server certificate matches one of the embedded certificates.

So here are the steps:

1. Retrieve the certificate from the website.

   • Open the site on Safari
   • Click on the padlock icon near the website name
   • Click on Show Certificate
   • Drag and drop the certificate in a folder

see https://www.markbrilman.nl/2012/03/howto-save-a-certificate-via-safari-on-mac/

2. Copy the certificate (.cer file) into the res/raw folder of your app

3. In your code, load the certificate(s) by calling loadSSLCertificates()

   private static final int[] CERTIFICATES = {
           R.raw.my_certificate,   // you can put several certificates
   };
   private ArrayList<SslCertificate> certificates = new ArrayList<>();
   
   private void loadSSLCertificates() {
       try {
           CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
           for (int rawId : CERTIFICATES) {
               InputStream inputStream = getResources().openRawResource(rawId);
               InputStream certificateInput = new BufferedInputStream(inputStream);
               try {
                   Certificate certificate = certificateFactory.generateCertificate(certificateInput);
                   if (certificate instanceof X509Certificate) {
                       X509Certificate x509Certificate = (X509Certificate) certificate;
                       SslCertificate sslCertificate = new SslCertificate(x509Certificate);
                       certificates.add(sslCertificate);
                   } else {
                       Log.w(TAG, "Wrong Certificate format: " + rawId);
                   }
               } catch (CertificateException exception) {
                   Log.w(TAG, "Cannot read certificate: " + rawId);
               } finally {
                   try {
                       certificateInput.close();
                       inputStream.close();
                   } catch (IOException e) {
                       e.printStackTrace();
                   }
               }
           }
       } catch (CertificateException e) {
           e.printStackTrace();
       }
   }
   

4. When a SslError occurs, check that the server certificate matches one embedded certificate. Note that it is not possible to directly compare certificates, so I use SslCertificate.saveState to put the certificate data into a Bundle, and then I compare all the bundle entries.

   webView.setWebViewClient(new WebViewClient() {
   
       @Override
       public void onReceivedSslError(WebView view, final SslErrorHandler handler, SslError error) {
   
           // Checks Embedded certificates
           SslCertificate serverCertificate = error.getCertificate();
           Bundle serverBundle = SslCertificate.saveState(serverCertificate);
           for (SslCertificate appCertificate : certificates) {
               if (TextUtils.equals(serverCertificate.toString(), appCertificate.toString())) { // First fast check
                   Bundle appBundle = SslCertificate.saveState(appCertificate);
                   Set<String> keySet = appBundle.keySet();
                   boolean matches = true;
                   for (String key : keySet) {
                       Object serverObj = serverBundle.get(key);
                       Object appObj = appBundle.get(key);
                       if (serverObj instanceof byte[] && appObj instanceof byte[]) {     // key "x509-certificate"
                           if (!Arrays.equals((byte[]) serverObj, (byte[]) appObj)) {
                               matches = false;
                               break;
                           }
                       } else if ((serverObj != null) && !serverObj.equals(appObj)) {
                           matches = false;
                           break;
                       }
                   }
                   if (matches) {
                       handler.proceed();
                       return;
                   }
               }
           }
   
           handler.cancel();
           String message = "SSL Error " + error.getPrimaryError();
           Log.w(TAG, message);
       }
   
   
   });
   

Answer 3

I needed to check our truststore before show any message to the user so I did this:

public class MyWebViewClient extends WebViewClient {
private static final String TAG = MyWebViewClient.class.getCanonicalName();

Resources resources;
Context context;

public MyWebViewClient(Resources resources, Context context){
    this.resources = resources;
    this.context = context;
}

@Override
public void onReceivedSslError(WebView v, final SslErrorHandler handler, SslError er){
    // first check certificate with our truststore
    // if not trusted, show dialog to user
    // if trusted, proceed
    try {
        TrustManagerFactory tmf = TrustManagerUtil.getTrustManagerFactory(resources);

        for(TrustManager t: tmf.getTrustManagers()){
            if (t instanceof X509TrustManager) {

                X509TrustManager trustManager = (X509TrustManager) t;

                Bundle bundle = SslCertificate.saveState(er.getCertificate());
                X509Certificate x509Certificate;
                byte[] bytes = bundle.getByteArray("x509-certificate");
                if (bytes == null) {
                    x509Certificate = null;
                } else {
                    CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
                    Certificate cert = certFactory.generateCertificate(new ByteArrayInputStream(bytes));
                    x509Certificate = (X509Certificate) cert;
                }
                X509Certificate[] x509Certificates = new X509Certificate[1];
                x509Certificates[0] = x509Certificate;

                trustManager.checkServerTrusted(x509Certificates, "ECDH_RSA");
            }
        }
        Log.d(TAG, "Certificate from " + er.getUrl() + " is trusted.");
        handler.proceed();
    }catch(Exception e){
        Log.d(TAG, "Failed to access " + er.getUrl() + ". Error: " + er.getPrimaryError());
        final AlertDialog.Builder builder = new AlertDialog.Builder(context);
        String message = "SSL Certificate error.";
        switch (er.getPrimaryError()) {
            case SslError.SSL_UNTRUSTED:
                message = "O certificado não é confiável.";
                break;
            case SslError.SSL_EXPIRED:
                message = "O certificado expirou.";
                break;
            case SslError.SSL_IDMISMATCH:
                message = "Hostname inválido para o certificado.";
                break;
            case SslError.SSL_NOTYETVALID:
                message = "O certificado é inválido.";
                break;
        }
        message += " Deseja continuar mesmo assim?";

        builder.setTitle("Erro");
        builder.setMessage(message);
        builder.setPositiveButton("Sim", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                handler.proceed();
            }
        });
        builder.setNegativeButton("Não", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                handler.cancel();
            }
        });
        final AlertDialog dialog = builder.create();
        dialog.show();
    }
}
}

Answer 4

Fix which works for me is just disable onReceivedSslError function defined in AuthorizationWebViewClient. In this case handler.cancel will be called in case of SSL error. However it works good with One Drive SSL certificates. Tested on Android 2.3.7, Android 5.1.

Answer 5

According to Google Security Alert: Unsafe implementation of the interface X509TrustManager, Google Play won't support X509TrustManager from 11th July 2016:

Hello Google Play Developer,

Your app(s) listed at the end of this email use an unsafe implementation of the interface X509TrustManager. Specifically, the implementation ignores all SSL certificate validation errors when establishing an HTTPS connection to a remote host, thereby making your app vulnerable to man-in-the-middle attacks. An attacker could read transmitted data (such as login credentials) and even change the data transmitted on the HTTPS connection. If you have more than 20 affected apps in your account, please check the Developer Console for a full list.

To properly handle SSL certificate validation, change your code in the checkServerTrusted method of your custom X509TrustManager interface to raise either CertificateException or IllegalArgumentException whenever the certificate presented by the server does not meet your expectations. For technical questions, you can post to Stack Overflow and use the tags “android-security” and “TrustManager.”

Please address this issue as soon as possible and increment the version number of the upgraded APK. Beginning May 17, 2016, Google Play will block publishing of any new apps or updates containing the unsafe implementation of the interface X509TrustManager.

To confirm you’ve made the correct changes, submit the updated version of your app to the Developer Console and check back after five hours. If the app hasn’t been correctly upgraded, we will display a warning.

While these specific issues may not affect every app with the TrustManager implementation, it’s best not to ignore SSL certificate validation errors. Apps with vulnerabilities that expose users to risk of compromise may be considered dangerous products in violation of the Content Policy and section 4.4 of the Developer Distribution Agreement.

...

Answer 6

I had the same issue and tried all the above-mentioned suggestions as below.

1. Implement onReceivedSslError() by giving the chance to the user to decide handler.proceed(); or handler.cancel(); when a SSL error occurred
2. Implement onReceivedSslError() to call handler.cancel(); whenever a SSL issue occurred without considering user's decision.
3. Implement onReceivedSslError() to verify SSL certificate locally addition to checking error.getPrimaryError() and providing the user to decide handler.proceed(); or handler.cancel(); only if the SSL certificate is valid. If not just call handler.cancel();
4. Removing the implementation of onReceivedSslError() and just let to happen Android default behavior.

Even after trying all the above attempts, Google Play was keeping sending the same notification mail mentioning the same error and the old APK version (Even though in the all above attempts we changed both version code and version name in the Gradle)

We were in huge trouble and contacted Google Support via mail and asked

"We are uploading the higher versions of the APK but the review result says the same error mentioning the old buggy APK version. What's the reason for that ?"

After a few days, google support replied to our request as follows.

Please note that you must completely replace version 12 in your Production track. It means that you'll have to full rollout a higher version in order to deactivate version 12.

The highlighted point was never found or mentioned in the play console or any forum.

According to that guideline in the classic Google play view, we checked the production track and there were both buggy versions and the latest bug fixed version but the bug fix version's rollout percentage is 20%. So, turned it to full rollout then the buggy version disappeared from the production track. After more than 24 hour review time version has come back.

NOTE: When we had this issue Google has just moved to a new UI version of their play console and it had missed some views in the previous UI version or classic view. Since we were using the latest view we couldn't notice what was happening. Simply what happened was Google reviewed the same previous buggy version of the APK since the new one was not full roll-out.

Answer 7

You can use SslError for show, some information about the error of this certificated, and you can write in your dialog the string of the type error.

@Override
public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
    final SslErrorHandler handlerFinal;
    handlerFinal = handler;
    int mensaje ;
    switch(error.getPrimaryError()) {
        case SslError.SSL_DATE_INVALID:
            mensaje = R.string.notification_error_ssl_date_invalid;
            break;
        case SslError.SSL_EXPIRED:
            mensaje = R.string.notification_error_ssl_expired;
            break;
        case SslError.SSL_IDMISMATCH:
            mensaje = R.string.notification_error_ssl_idmismatch;
            break;
        case SslError.SSL_INVALID:
            mensaje = R.string.notification_error_ssl_invalid;
            break;
        case SslError.SSL_NOTYETVALID:
            mensaje = R.string.notification_error_ssl_not_yet_valid;
            break;
        case SslError.SSL_UNTRUSTED:
            mensaje = R.string.notification_error_ssl_untrusted;
            break;
        default:
            mensaje = R.string.notification_error_ssl_cert_invalid;
    }

    AppLogger.e("OnReceivedSslError handel.proceed()");

    View.OnClickListener acept = new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            dialog.dismiss();
            handlerFinal.proceed();
        }
    };

    View.OnClickListener cancel = new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            dialog.dismiss();
            handlerFinal.cancel();
        }
    };

    View.OnClickListener listeners[] = {cancel, acept};
    dialog = UiUtils.showDialog2Buttons(activity, R.string.info, mensaje, R.string.popup_custom_cancelar, R.string.popup_custom_cancelar, listeners);    }

Answer 8

In my situation:This error occured when we try to updated apk uploaded into the Google Play store,and getting SSL Error: Then i have used following code

private class MyWebViewClient extends WebViewClient {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;
        }

        @Override
        public void onPageFinished(WebView view, String url) {
            try {
                progressDialog.dismiss();
            } catch (WindowManager.BadTokenException e) {
                e.printStackTrace();
            }
            super.onPageFinished(view, url);
        }

        @Override
        public void onReceivedSslError(WebView view, final SslErrorHandler handler, SslError error) {

 final AlertDialog.Builder builder = new AlertDialog.Builder(PayNPayWebActivity.this);
            builder.setMessage(R.string.notification_error_ssl_cert_invalid);
            builder.setPositiveButton("continue", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    handler.proceed();
                }
            });
            builder.setNegativeButton("cancel", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    handler.cancel();
                }
            });
            final AlertDialog dialog = builder.create();
            dialog.show();
        }
    }