Vulnerability Note VU#107886

ISC dhclient vulnerability

Overview

The ISC dhclient contains a vulnerability that could allow a remote attacker to execute arbitrary code on the client machine.

I. Description

According to ISC:

ISC dhclient did not strip or escape certain shell meta-characters in responses from the dhcp server (like hostname) before passing the responses on to dhclient-script. Depending on the script and OS, this can result in execution of exploit code on the client.

II. Impact

An unauthenticated remote attacker could cause the ISC dhclient to execute arbitrary code on the client machine.

III. Solution

Apply an update

Users who obtain ISC DHCP from a third-party vendor, such as their operating system vendor, should see the vendor information portion of this document for a partial list of affected vendors.

This vulnerability is addressed in ISC DHCP version 3.1-ESV-R1, 4.1-ESV-R2 and 4.2.1-P1. Users of ISC DHCP from the original source distribution should upgrade to this version or later, as appropriate.

See also https://www.isc.org/software/dhcp/advisories/cve-2011-0997
According to ISC:
On SUSE systems, it is possible to disable hostname update by setting DHCLIENT_SET_HOSTNAME="no" in /etc/sysconfig/network/dhcp.
Other systems may add following line to dhclient-script at the beginning of the set_hostname() function:

new_host_name=${new_host_name//[^-.a-zA-Z0-9]/}

In environments where filters/acls can be put into place to limit clients to accessing only legitimate dhcp servers, this will protect clients
from rogue dhcp servers deliberately trying to exploit this bug. However, this will not protect from compromised servers.

Vendor Information

Vendor	Status	Date Notified	Date Updated
Debian GNU/Linux	Affected		2011-04-25
Fedora Project	Affected		2011-04-25
Internet Systems Consortium	Affected		2011-04-05
Mandriva S. A.	Affected		2011-04-25
Red Hat, Inc.	Affected		2011-04-25
Slackware Linux Inc.	Affected		2011-04-25
Ubuntu	Affected		2011-04-25
Wind River Systems, Inc.	Not Affected	2011-04-08	2011-05-06

References

https://www.isc.org/software/dhcp/advisories/cve-2011-0997

Credit

Thanks to Sebastian Krahmer and Marius Tomaschewski at SUSE Security Team for reporting this vulnerability to Internet Systems Consortium.

This document was written by Michael Orlando.

Other Information

Date Public:	2011-04-05
Date First Published:	2011-04-05
Date Last Updated:	2011-05-06
CERT Advisory:
CVE-ID(s):	CVE-2011-0997
NVD-ID(s):	CVE-2011-0997
US-CERT Technical Alerts:
Severity Metric:	11.34
Document Revision:	10