A security feature bypass vulnerability exists in the Microsoft Chakra scripting engine that allows Control Flow Guard (CFG) to be bypassed. By itself, the CFG bypass vulnerability does not allow arbitrary code execution. However, an attacker could use the CFG bypass vulnerability in conjunction with another vulnerability, such as a remote code execution vulnerability, to run arbitrary code on a target system. To exploit the CFG bypass vulnerability, a user must be logged on to the Microsoft Chakra scripting engine and running it. The user would then need to browse to a malicious website. The security update addresses the CFG bypass vulnerability by helping to ensure that the Microsoft Chakra scripting engine properly handles accessing memory.