Defender Application Control or Defender SmartScreen – what can you do to not be blocked by it

Ever wondered why do you get one of these popups for your Windows program, despite of the fact that it is signed with a standard code signing certificate ?

Applications that are signed with a standard code signing certificates need to have a positive reputation in order to pass the Smart Screen filter. Microsoft establishes the reputation of an executable based upon the number of installations world wide of the same application. Since you haven’t published your application as yet (and therefore the reputation hasn’t been established as yet), the Smart Screen will continue to flag the application.

If you have a standard code signing certificate, some time will be needed for your application to build trust. Microsoft affirms that an Extended Validation (EV) Code Signing Certificate allows to skip this period of trust building.

According to Microsoft, extended validation certificates allow the developer to immediately establish reputation with SmartScreen. Otherwise, for some time, until your application builds trust, the users will see a warning like “Windows Defender Smartscreen prevented an unrecognized app from starting. Running this app might put your PC at risk.”, with the two buttons: “Run anyway” and “Don’t run”. In newer Windows version you see the text in the popup above and below.

There are two solutions:

  1. either wait until the application has a large user base and its reputation will be adjusted by the Smart Screen. However, the current working status might prevent users from installing and trusting the application.
  2. sign it with an EV (Extended Validation) code signing certificate. Applications signed with an EV certificate establishes its reputation right away.

To quote Microsoft: “Programs signed by an EV code signing certificate can immediately establish reputation with SmartScreen reputation services even if no prior reputation exists for that file or publisher. ”

You can find further details at Microsoft SmartScreen & Extended Validation (EV) Code Signing Certificates blogpost. Another Microsoft resource states the following (quote): “Although not required, programs signed by an EV code signing certificate can immediately establish reputation with SmartScreen reputation services even if no prior reputation exists for that file or publisher. EV code signing certificates also have a unique identifier which makes it easier to maintain reputation across certificate renewals.”

 

Questions unanswered:

If you use a standard CS certificate, why do you get the popup only on some computers, while you never see it on others? Isn’t the Smart Screen the same ? Of course it is…

I assume that the computer downloads some database with certificates when it needs to. If you’re lucky, your certificate is there and you don’t see the popup.

 

Source: various posts on stackexchange.com and msdn.microsoft.com


© Copyright 2020 Sorin Mustaca, All rights Reserved. Written For: Sorin Mustaca on Cybersecurity


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About the Author

Sorin Mustaca
Sorin Mustaca, (ISC)2 CSSLP, CompTIA Security+ and Project+, is working since year 2000 in the IT Security industry and worked between 2003-2014 for Avira as Product Manager for the known products used by over 100 million users world-wide. Today he is an independent IT Security Consultant focusing on Cybersecurity, secure software development and security for IoT and Automotive. He is also running his personal blog Sorin Mustaca on Cybersecurity and is the author of the free eBook Improve your security .
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