"export file=123" hangs after /routing ospf interface (all interfeces are output). ^C does not work. Closing telnet connection does not stop export too.
Is there a way to kill an active user? Like "user active remove"?
CPU usage is 100% because of that export and I'd like not reboot the mikrotik.
RouterOS version 3.24

unfortunately you can't remove active users.
However if you execute export command from console, it will show as an entry in "/system script job" menu which you can remove.

Upgrade to v3.25, if problem remains, generate supout file and send it to support [at] mikrotik.com

"/system script job remove" did the trick! Thank you!
BTW, is it possible to output a detailed info of which command is being executed in the job?

not really.
console commands will show with no script name
/but for exampel if you do /system script run myScript
then it will show that myScript is running.