A Verifier DLL is a dynamic link library used with Microsoft’s Application Verifier tool to monitor and detect bugs in Windows applications.
Verifier DLLs can be abused by attackers to hook arbitrary functions.
https://learn.microsoft.com/en-us/windows-hardware/drivers/devtest/application-verifier
https://securitymaven.medium.com/anatomy-of-a-verifier-dll-88c269baa524