Same here! - Can mobileCore fix it by updating their certificate?
Now the Notice appeared in my Console too for all Apps with MobileCore. Anybody contacted MobileCore support yet?
Same thing here for all my apps any solutions ?
That confirms the issue is with mobilecore. That sucks man!!
I already mailed my manager but she is slow to respond.
I have also mailed the google play support team, once they get back at me will update for the same.
I just got this email from Google
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.
Apps must also comply with the Developer Distribution Agreement and Content Policy. If you feel we have sent this warning in error, contact our policy support team through the Google Play Developer Help Center.
Regards,
The Google Play Team
©2016 Google Inc. 1600 Amphitheatre Parkway, Mountain View, CA 94043
Email preferences: You have received this mandatory email service announcement to update you about important changes to your Google Play Developer account.
Affected app(s), version(s), and class(es):
com.xxxxx.xxxxx.xxxxx.xxxxxx
7
com.ironsource.mobilcore.C$1;
Same here 
Any solutions?
same looks like its because the sticky ads ?
I will search a new ad network mobilecore is for me to unsafe.
Because i dont that google block my apps 
I’m just, I have received emails accounts, although not all, but the error was pointed directly at Mobilecore.
By the way this morning update an app removing Mobilecore SDK. And even with the warning continues.
expect to Mobilecore rule, I imagine that will update your SDK
Alert Removed when i removed mobilecore
Great. Thanks for updating us. 
Removed mobilecore and released an Update. Later there is no any new alerts coming to my console. But the OLD alerts are remained. Anyhow there are of previous APK versions.
Anyone with an AM of mC online in Skype? I just added my AM and she is not online yet.
Have you told them about the problem? Removing a good network is not the solution
Yes. What you said is true. Me too waiting for the solution from them.
Hello there,
can anyone tell me what this google alert means: Your app is using an unsafe implementation of the X509TrustManager interface with an Apache HTTP client, resulting in a security vulnerability. Please see this Google Help Center article for details, including the deadline for fixing the vulnerability.
Affects APK version1. I don’t even know what to do or how to fix it…help.
dont spam and just read this thread
ok…first i’m using a forum. just a bit frustrated with the alert. i only have one app on google play.
Just got a reply from my MC account manager:
[i]Dear Developer,
We are aware that in preparation of its enforcement this upcoming May, Google has been issuing more security alerts than usual. We are constantly updating and improving our SDK and we assure you that required adjustments or any needed changes will be done as soon as possible. Please feel free to contact us with any concern or question you may have.
Best regards,
ironSource Mobile Ltd.[/i]
So we just have to wait until they update the SDK.