We often get questions about Certificate Pinning in mobile applications. Many clients find the issue difficult to explain to other teams.

You can find really great write ups, and an excellent set of source code examples for fixing this issue – as well as explaining it – at this OWASP.org site.

At a super high level though, you basically want your mobile application to validate the SSL certificate of the specific server(s) that you want it to talk to, and REJECT any certificates that do not match the intended server certificate – REGARDLESS of whether or not the underlying OS trusts the alternative certificate.

This will go a long way to hardening the SSL communication streams between the app and the server, and will not permit easy interception or man-in-the-middle attacks via a network provider or hostile proxy server.

Updates to the app source code are needed to mitigate the issue, and you may need to update apps in the app stores, depending on the way your app is delivered.

As always, if you work with MSI on mobile app security reviews or application-specific penetration testing, we would be happy to demonstrate the attacks and suggested mitigations for any identified issue. Just let us know if you would like assistance.

As always, thanks for reading and I hope your team finds this useful.