USN-1571-1: DHCP vulnerability

18 September 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


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


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

To update your system, please follow these instructions:

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