Update problem

Hello,
I'm having trouble updating glibc in a particular server.
when I run yum update glibc, the following output is displayed :

Loading "installonlyn" plugin
Setting up Update Process
Setting up repositories
No Repositories Available to Set Up
Reading repository metadata in from local files
Could not find update match for glibc
No Packages marked for Update/Obsoletion

There is only one repo in the yum dir :

[root@srv ~]# cd /etc/yum.repos.d/
[root@srv yum.repos.d]# ls
rhel-debuginfo.repo

this is the OS version installed on the server : Red Hat Enterprise Linux Server release 5.1 (Tikanga)

Please keep in mind that the Ghost vulnerability is very critical and we need to update ASAP.

Thank you