Open Stack

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glibc 'GHOST' vulnerability can allow remote code execution
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### Summary ###
A serious vulnerability in the GNU C library (glibc) gethostbyname*
functions can allow an attacker to perform remote code execution with
the privileges of the application that calls the gethostbyname*
function. The vulnerable functions are used by a vast number of
programs, effectively any time a network socket is used in a linux
system, so the full exploitability of this vulnerability will not
become known immediately.

The publishers of this vulnerability, Qualys, have announced a proof of
concept exploit for the Exim mail server, which bypasses operating
system protections such as ASLR and DEP.


### Affected Services / Software ###
All versions running on Linux installations with a vulnerable glibc
library.

### Discussion ###
The GNU C library (glibc), from versions 2.2 to 2.17 inclusive, has
a group of vulnerable functions for hostname/address resolution. There
is a buffer overflow in the __nss_hostname_digits_dots() function which
is used by the gethostbyname*() group of functions. The maximum amount
of memory that can be overwritten is sizeof(char *), i.e. 4 bytes on
typical 32-bit systems and 8 bytes on typical 64-bit systems.

These low-level functions are linked by many other C/C++ programs and
interpreted languages like Python, Perl and Bash, so this vulnerability
is insidious and will appear in cases where it would not at first seem
obvious. There are many cases in a typical Linux installation where
these functions will be used, generally wherever a hostname is resolved
to an IP address, although in newer applications an IPv6 compatible
function, getaddinfo() may be used instead.

This vulnerability could let an attacker remotely execute code in cases
where they control the input to a function that performs hostname
resolution. There are no currently-known OpenStack-specific
exploitation paths associated with this vulnerability. However, the
Python socket library presents a gethostbyname() wrapper around the
glibc function, and there are various ways in which this could be
exposed.

### Recommended Actions ###
The glibc library is loaded into memory when a process that uses it
starts up, so to fix the vulnerability, glibc should be updated to a
non-vulnerable version (2.18 or newer) and all services which use glibc
should be restarted to replace the version in memory. Due to the number
of places where these vulnerable functions are used, this effectively
means that vulnerable systems must be restarted after updating glibc.

### Contacts / References ###
This OSSN : https://wiki.openstack.org/wiki/OSSN/OSSN-0043
Original LaunchPad Bug : https://bugs.launchpad.net/ossn/+bug/1415416
OpenStack Security ML : openstack-security at lists.openstack.org
OpenStack Security Group : https://launchpad.net/~openstack-ossg
CVE: CVE-2015-0235
Source advisory:
https://www.qualys.com/research/security-advisories/GHOST-CVE-2015-0235.txt
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