Microsoft SharePoint Server Spoofing Vulnerability

According to the CVSS metrics, successful exploitation of this vulnerability could lead to some loss of integrity (I:L)? What does that mean for this vulnerability?
Integrity is impacted as XSS allows an attacker to add their malicious script to fetch victim's sensitive info or to change DOM execution.

According to the CVSS metric, privileges required is low (PR:L). What does that mean for this vulnerability?
The attacker must be authenticated to the target site as at least a Site Member.

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

There are multiple update packages available for some of the affected software. Do I need to install all the updates listed in the Security Updates table for the software?
Yes. Customers should apply all updates offered for the software installed on their systems. If multiple updates apply, they can be installed in any order.

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

Security updates
16.0.5483.1001 — https://support.microsoft.com/help/5002672
16.0.5483.1001 — https://support.microsoft.com/help/5002671
16.0.10416.20041 — https://support.microsoft.com/help/5002666
16.0.10416.20041 — https://support.microsoft.com/help/5002667
16.0.17928.20356 — https://support.microsoft.com/help/5002676