In Nagios XI through 5.8.5, in the schedule report function, an authenticated attacker is able to inject HTML tags that lead to the reformatting/editing of emails from an official email address.
In Nagios XI through 5.8.5, a read-only Nagios user (due to an incorrect permission check) is able to schedule downtime for any host/services. This allows an attacker to permanently disable all monitoring checks.
An issue was discovered in Nagios XI 5.8.5. Insecure file permissions on the nagios_unbundler.py file allow the nagios user to elevate their privileges to the root user.
An issue was discovered in Nagios XI 5.8.5. In the Custom Includes section of the Admin panel, an administrator can upload files with arbitrary extensions as long as the MIME type corresponds to an image. Therefore it is possible to upload a crafted PHP script to achieve remote command execution.