I took the latest release from log4net, version 2.0.17.
Grabbed the DLL from the net45 folder and replaced it in my local install of FineCodeCoverage, which seems to get rid of the vulnerability flagging and FineCodeCoverage extension seem to still run just fine.
Hello, this extension is being flagged with a critical vulnerability
Looks like FineCodeCoverage is using an extremely old version of Apache log4net, they already had a fix for this 4 years ago. https://github.com/apache/logging-log4net/releases