Typical severity: Very High. Likelihood of attack: High. Generally these are manually edited files that are not in the preview of the system administrators, any ability on the attackers' behalf to modify these files, for example in a CVS repository, gives unauthorized access directly to the application, the same as authorized users.
Design: Enforce principle of least privilege | Design: Backup copies of all configuration files | Implementation: Integrity monitoring for configuration files | Implementation: Enforce audit logging on code and configuration promotion procedures. | Implementation: Load configuration from separate process and memory space, for example a separate physical device like a CD