According to CERT, this vulnerability has been actively exploited in the wild before official patch release.
Vulnerable component: Microsoft Word
CVSSv3 score: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H/E:F/RL:O/RC:C
CWE-ID: CWE-119 - Improper Restriction of Operations within the Bounds of a Memory Buffer
The vulnerability allows a remote user to execute arbitrary code on the target system.
The vulnerability exists due to boundary error when handling malformed stream in Word document. A remote attacker can create a specially crafted MS Word document, trick the victim into opening it and execute arbitrary code with privileges of the current user.
Successful exploitation of the vulnerability results in compromise of vulnerable system.
Note: this vulnerability is being actively exploited.