To know how ConnectALL handles the Log4j 2 vulnerability issue, please read the article here.

Is it possible to write custom business rules for an application link?

Yes! Mule ESB allows business logic to be injected into the Mule Flows, and it is the same with ConnectALL. You have to modify the default flows that come with ConnectALL, and no changes are required on the product. Need help? Reach out to us.