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Ubuntu: Security update for ISC DHCP server

Glen Eustace discovered that the DHCP server incorrectly handled IPv6 expiration times. A remote attacker could use this issue to cause DHCP to crash, resulting in a denial of service. Dan Rosenberg discovered that the DHCP AppArmor profile could be escaped by using environment variables. This update mitigates the issue by sanitizing certain variables in the DHCP shell scripts.

Updated packages are available from security.ubuntu.com.

==========================================================================
Ubuntu Security Notice USN-1571-1
September 18, 2012

dhcp3, isc-dhcp vulnerability
==========================================================================

A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 12.04 LTS
- Ubuntu 11.10
- Ubuntu 11.04
- Ubuntu 10.04 LTS

Summary:

DHCP could be made to crash if it received specially crafted network
traffic.

Software Description:
- isc-dhcp: DHCP server and client
- dhcp3: DHCP server and client

Details:

Glen Eustace discovered that the DHCP server incorrectly handled IPv6
expiration times. A remote attacker could use this issue to cause DHCP to
crash, resulting in a denial of service. This issue only affected Ubuntu
11.04, Ubuntu 11.10 and Ubuntu 12.04 LTS. (CVE-2012-3955)

Dan Rosenberg discovered that the DHCP AppArmor profile could be escaped by
using environment variables. This update mitigates the issue by sanitizing
certain variables in the DHCP shell scripts.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 12.04 LTS:
 isc-dhcp-client                 4.1.ESV-R4-0ubuntu5.5
 isc-dhcp-server                 4.1.ESV-R4-0ubuntu5.5

Ubuntu 11.10:
 isc-dhcp-client                 4.1.1-P1-17ubuntu10.5
 isc-dhcp-server                 4.1.1-P1-17ubuntu10.5

Ubuntu 11.04:
 isc-dhcp-client                 4.1.1-P1-15ubuntu9.6
 isc-dhcp-server                 4.1.1-P1-15ubuntu9.6

Ubuntu 10.04 LTS:
 dhcp3-client                    3.1.3-2ubuntu3.4
 dhcp3-server                    3.1.3-2ubuntu3.4

In general, a standard system update will make all the necessary changes.

References:
 http://www.ubuntu.com/usn/usn-1571-1
 CVE-2012-3955, https://launchpad.net/bugs/1016643

Package Information:
 https://launchpad.net/ubuntu/+source/isc-dhcp/4.1.ESV-R4-0ubuntu5.5
 https://launchpad.net/ubuntu/+source/isc-dhcp/4.1.1-P1-17ubuntu10.5
 https://launchpad.net/ubuntu/+source/isc-dhcp/4.1.1-P1-15ubuntu9.6
 https://launchpad.net/ubuntu/+source/dhcp3/3.1.3-2ubuntu3.4
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