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GHOST: The glibc's gethostbyname vulnerability


On January 27, 2015, a vulnerability named "GHOST" in the glibc library was publicly announced. GHOST is also referred as CVE-2015-0235. The vulnerability is a buffer overflow in the gethostbyname family of functions that can allow arbitrary code execution.

Affected Products

  • TMG800, TMG3200, TMG7800-CTRL
  • Tdev Linux server with (CentOS, RedHat, etc) running Toolpack software

Details

The impact of this vulnerability on TelcoBridges products depends on their configuration. The vulnerability may only be triggered through requests for domain name resolution. Therefore, only units that enable such services may be exposed to the issue.

Software Versions and Fixes

The TelcoBridges CentOS 5 repository has been updated with the latest glibc version. Services that use glibc must be restarted. Because glibc is thoroughly used in the Linux operating system, it is highly recommended to reboot the unit.

Update procedure

The operator can use one of the two methods available: GUI/WebPortal or command line interface.

WebPortal - TMG unit or Linux server with access to Internet (i.e. with DNS configured)

  1. login onto the WebPortal
  2. Select the 'Hosts' section
  3. Click on the hostname
  4. Click on the 'Status' tab
  5. Select 'Upgrade Linux packages' into the host 'Action'
  6. Click on the 'Apply action' button
  7. Refresh the page until the packages are updated as indicated in the 'Action Log' (you may use the 'Now' button to update the page). The results should appear within a minute.
  8. Select 'Shutdown' into the host 'Action'
  9. Select 'Reboot' into the 'Shutdown Type'
  10. Click on the 'Apply action' button
  11. Repeat the process for all hosts listed

Command line interface

  • login with root account
[root@TB011107 ~]# uname -m
x86_64
  • If the result is not "x86_64", please contact TelcoBridges support, otherwise you can proceed with either method below.
  • Follow one of the two options depending if Internet is accessible from the unit

Option #1 - TMG unit or Linux server with access to Internet (i.e. with DNS configured)

  • update OS packages with yum
yum clean all
yum update
  • reboot the unit
reboot

Option #2 - TMG unit or Linux server without access to Internet

yum localinstall glibc-2.5-123.el5_11.1.x86_64.rpm \
  glibc-common-2.5-123.el5_11.1.x86_64.rpm \
  glibc-devel-2.5-123.el5_11.1.x86_64.rpm \
  glibc-headers-2.5-123.el5_11.1.x86_64.rpm \
  nscd-2.5-123.el5_11.1.x86_64.rpm
  • Note: that operation might take a long time since yum will probably experience timeouts when trying to access the external repositories.
  • Reboot the unit
reboot

How to verify if the vulnerability is fixed?

  • login with root account
  • execute the following to create a test script
cat > rhel-GHOST-test.sh << FOF
#!/bin/bash
# rhel-GHOST-test.sh -  GHOST vulnerability tester. Only for CentOS/RHEL based servers.  #
# Version 3
# Credit : Red Hat, Inc - https://access.redhat.com/labs/ghost/ #
echo "Installed glibc version(s)"

rv=0
for glibc_nvr in \$( rpm -q --qf '%{name}-%{version}-%{release}.%{arch}\n' glibc ); do
    glibc_ver=\$( echo "\$glibc_nvr" | awk -F- '{ print \$2 }' )
    glibc_maj=\$( echo "\$glibc_ver" | awk -F. '{ print \$1 }')
    glibc_min=\$( echo "\$glibc_ver" | awk -F. '{ print \$2 }')

    echo -n "- \$glibc_nvr: "
    if [ "\$glibc_maj" -gt 2 -o \( "\$glibc_maj" -eq 2  -a  "\$glibc_min" -ge 18 \) ]; then
        # fixed upstream version
        echo 'not vulnerable'
    else
        # all RHEL updates include CVE in rpm %changelog
        if rpm -q --changelog "\$glibc_nvr" | grep -q 'CVE-2015-0235'; then
            echo "not vulnerable"
        else
            echo "vulnerable"
            rv=1
        fi
    fi
done

if [ \$rv -ne 0 ]; then
    cat <<EOF

This system is vulnerable to CVE-2015-0235. <https://access.redhat.com/security/cve/CVE-2015-0235>
Please refer to <https://access.redhat.com/articles/1332213> for remediation steps
EOF
fi

exit \$rv

FOF
  • Execute the script
chmod +x rhel-GHOST-test.sh
./rhel-GHOST-test.sh
  • You should not see the 'vulnerable' string displayed


Verify system timezone

We found that some systems got the timezone reset to EST time after the GHOST patch procedures

  • Verify the timezone on the system
date

If it differs from the original, reset the timezone using the tbtimezone script.


References