The Deny Directive for the OS root should be configured appropriately
(1) all | hostname/IP address/environment variable
(1) Deny directive
L1 13. Access Control Directives p21
1.7 Restricting Access p14-15
CIS Apache Benchmark for Unix v1.7 For Apache Versions 1.3 and 2.0
CIS
2007-07-01
Version 1.7
Prose (PDF)
Security Configuration Benchmark For Apache Web Server
CIS
2008-11-01
Version 2.2.0
Prose (PDF)