|GFI has released an official statement|
Log4j hotfix against Log4Shell (CVE-2021-44228) for Kerio Connect server instances running on Ubuntu 20.04. Please note that at this point it is unclear to me if Kerio Connect is vulnerable. This is meant as a precaution.
JndiLookup class from
log4j-core-2.5.jar. I haven't run into any side effects, but be advised this might cause unintended side effects.