If you are running Apache version 2.2.17, I wonder that you install it from CentAlt repo. You can check it by using repoquery
program from yum-utils
package:
# repoquery -i httpd
Name : httpd
Version : 2.2.15
Release : 5.el6.centos
Architecture: x86_64
Size : 3057369
Packager : CentOS BuildSystem <http://bugs.centos.org>
Group : System Environment/Daemons
URL : http://httpd.apache.org/
Repository : base
Summary : Apache HTTP Server
Description :
The Apache HTTP Server is a powerful, efficient, and extensible
web server.
And if so, you can upgrade Apache to the latest version (2.2.20) from this repo with:
# yum update httpd
Verify the Apache version and restart httpd:
# httpd -v
Server version: Apache/2.2.20 (Unix)
Server built: Aug 31 2011 14:48:47
# service httpd restart
Take a look at error logs to confirm they are working fine.
PS: I strongly recommend you do it on the test server first.