There exists a "feature" in the x86 architecture that, due to improper programming by many operating system vendors, can be exploited to achieve local privilege escalation. At the time of discovery, this issue was present on the latest-and-greatest versions of Microsoft Windows, Apple's macOS, and certain distributions of Linux. This issue, very likely, impacts other operating systems on the x86 architecture.For both Intel and AMD CPUs, this vulnerability can be utilized to reliably and successfully exploit Windows 10 by replacing the access token of the current process with the SYSTEM token from an unprivileged and sandboxed usermode application. This results in local privilege escalation. On AMD hardware, if SMAP/SMEP is disabled, this vulnerability can be exploited without failure since arbitrary user-specified memory can be utilized in CPL 0.