The security aspect of the linuxmuster.net's packages is taken very seriously, and we will try our best to solve the security issues as soon as possible. If you wish to report a potential vulnerability, first thank you for your help and your interest ! That's what makes open source software so great.
Please simply send an email with the description of the problem to arnaud AT linuxmuster DOT net.
It's also possible to encrypt your report for more confidentiality: I have a PGP stored at https://keys.openpgp.org associated with the email above.