Lucee before 5.4.7.3 LTS and 6 before 6.1.1.118, when an attacker can place files on the server, is vulnerable to a protection mechanism failure that can let an attacker run code that would be expected to be blocked and access resources that would be expected to be protected.
The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.