Details for this vulnerability have not been published by NIST at this point. Descriptions from software vendor advisories for this issue are provided below.
From VID-95F306A6-0AEE-11EB-ADD4-08002728F74C:
Ruby on Rails blog:
Rails version 6.0.3.4 has been released! This version is a security
release and addresses one possible XSS attack vector in Actionable
Exceptions.
With Rapid7 live dashboards, I have a clear view of all the assets on my network, which ones can be exploited, and what I need to do in order to reduce the risk in my environment in real-time. No other tool gives us that kind of value and insight.
– Scott Cheney, Manager of Information Security, Sierra View Medical Center