Microsoft Edge in Windows 10 1703 allows an attacker to execute arbitrary code in the context of the current user when the Edge JavaScript scripting engine fails to handle objects in memory, aka "Scripting Engine Memory Corruption Vulnerability". This CVE ID is unique from CVE-2017-8499, CVE-2017-8520, CVE-2017-8548, and CVE-2017-8549.
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8521