Microsoft Excel Remote Code Execution Vulnerability

Is the Preview Pane an attack vector for this vulnerability?
No, the Preview Pane is not an attack vector.

According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do?
Exploitation of the vulnerability requires that a user open a specially crafted file.
In an email attack scenario, an attacker could exploit the vulnerability by sending the specially crafted file to the user and convincing the user to open the file., In a web-based attack scenario, an attacker could host a website (or leverage a compromised website that accepts or hosts user-provided content) containing a specially crafted file designed to exploit the vulnerability.
An attacker would have no way to force users to visit the website. Instead, an attacker would have to convince users to click a link, typically by way of an enticement in an email or instant message, and then convince them to open the specially crafted file.

Security updates
16.0.5188.100 — https://support.microsoft.com/kb/5001977
15.0.5363.1000 — https://support.microsoft.com/kb/5001993
15.0.5363.1000 — https://support.microsoft.com/kb/5001986