NCSC-TG-006: A Guide to Understanding Configuration Management in Trusted Systems, 28 March 1988. (Amber Book)
You can download it from the following link: https://packetstormsecurity.com/files/download/13997/NCSC-TG-006.txt
Source: https://packetstormsecurity.com/files/13997/NCSC-TG-006.txt.html