A new version (4.92.2) of Exim with a critical bugfix is due to be released tomorrow, 2019-09-06 10:00 UTC. Hopefully it will be available for update in custombuild shortly after?
More info: https://seclists.org/oss-sec/2019/q3/192
More info: https://seclists.org/oss-sec/2019/q3/192