Linux oriented operating systems affected  vulnerability, possibilities for remote attackers to access complete control of a system,this vulnerability is a critical and attacks many servers. Its works for buffer overflow bug in glibc's function.

Glibc 2.2 to 2.17 version are at risk so you want to update latest version based on different operating systems and versions..                                                                                       

Check System Vulnerability:

Simplest way to check  whether your servers are vulnerable to HOST with test your glibc version with below commands
  
Ubuntu / Debian:

#  ldd --version


ldd (GNU libc) 2.12

Copyright (C) 2010 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Written by Roland McGrath and Ulrich Drepper.


CentOS / RHEL
 
# rpm -q glibc
glibc-2.12-1.132.el6_5.4.x86_64


Which versions are Safe  your server:

The below glibc versions are matches in your operating system its safe from GHOST  vulnerability,

Ubuntu/Debian:

    Ubuntu 12.04 LTS: 2.15-0ubuntu10.10
    Ubuntu 10.04 LTS: 2.11.1-0ubuntu7.20
    Debian 7 LTS: 2.13-38+deb7u7

RHEL/CentOS

    RHEL 5: glibc-2.5-123.el5_11.1
    RHEL 6: glibc-2.12-1.149.el6_6.5
    RHEL 7: glibc-2.17-55.el7_0.5
    CentOS 6: glibc-2.12-1.149.el6_6.5
    CentOS 7: glibc-2.17-55.el7_0.5

How to Fix :​

We can fixed this GHOST vulnerability in easiest way,  update your glibc version using yum update or apt-get update,                                                                                         

Ubuntu / Debian:
 
#   sudo apt-get update && sudo apt-get dist-upgrade  -y

CentOS / RHEL

Update latest glibc package using yum command, for example below packages updates in server                  
                                               
#  yum update glibc  -y


Dependencies Resolved

==================================================================

 Package                         Arch          Version                            

==================================================================

Updating:                    

 glibc                           i686          2.12-1.149.el6_6.5            

 glibc                           x86_64        2.12-1.149.el6_6.5              

Updating for dependencies:   

 glibc-common                    x86_64        2.12-1.149.el6_6.5                  

 glibc-devel                     i686          2.12-1.149.el6_6.5          

 glibc-devel                     x86_64        2.12-1.149.el6_6.5          

 glibc-headers                   x86_64        2.12-1.149.el6_6.5          

 glibc-static                    x86_64        2.12-1.149.el6_6.5                       



Transaction Summary                           

==================================================================

Once installation completed reboot your system with below command,
 
# reboot
or
# init 6


Updated ?

Ubuntu / Debian:
 
#  ldd --version


ldd (Ubuntu EGLIBC 2.19-0ubuntu6.3) 2.19

Copyright (C) 2014 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Written by Roland McGrath and Ulrich Drepper
 
CentOS / RHEL 
 
# rpm -q glibc
glibc-2.12-1.149.el6_6.5.x86_64

or
 
# rpm -qa | grep glibc


glibc-static-2.12-1.149.el6_6.5.x86_64

glibc-common-2.12-1.149.el6_6.5.x86_64

glibc-2.12-1.149.el6_6.5.x86_64

glibc-devel-2.12-1.149.el6_6.5.x86_64

glibc-headers-2.12-1.149.el6_6.5.x86_64