I understand Libretime uses the Apache web server. So is Libretime affected by that bug? How to patch the system?
Libretime is not affected by this vulnerability. Keep you system up to date and you wont have any problem in that direction.
However, keep in mind that Libretime is an old software and is currently relying on old libaries that aren’t maintained anymore, so I personally recommend people to not consider Libretime as a really secure software.