Microsoft Windows win32kbase Use After Free MisterySnail NtGdiResetDC Privileged Escalation Exploit

CVE-2021-40449 is a use-after-free vulnerability in Win32k's NtGdiResetDC function. As with many other Win32k vulnerabilities, the root cause of this vulnerability lies in the ability to set user-mode callbacks and execute unexpected API functions during execution of those callbacks. The CVE-2021-40449 is triggered when the function ResetDC is executed a second time for the same handle during execution of its own callback.