Some questions about recent XSA-414

If this should be posted here instead, please move it.

Thankfully, Xen vulnerabilities that affect Qubes OS are very rare.

But I have some concerns about the recent XSA, and would like to understand its impact.
Is there any way I could make sure this vulnerability was not used to compromise my system in a short time window before updating?
Could such an attack be done stealthily, or would it be noticeable?

Memory corruption in xenstored or privilege escalation of a guest can’t be ruled out.

Does privilege escalation here mean full compromise?
Thank you for answers.

This is probably a question for @marmarek.