10 - USN-803-2

A security issue affects the following Ubuntu releases:

Ubuntu 8.10 Ubuntu 9.04 Ubuntu 9.10

This advisory also applies to the corresponding versions of Kubuntu, Edubuntu, and Xubuntu.

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

Ubuntu 8.10:
dhcp3-client 3.1.1-1ubuntu2.2
dhcp3-client-udeb 3.1.1-1ubuntu2.2

Ubuntu 9.04:
dhcp-client 3.1.1-5ubuntu8.2
dhcp3-client 3.1.1-5ubuntu8.2

Ubuntu 9.10:
dhcp-client 3.1.2-1ubuntu7.1
dhcp3-client 3.1.2-1ubuntu7.1

After a standard system upgrade you need to restart any DHCP network connections utilizing dhclient3 to effect the necessary changes.

Details follow:

USN-803-1 fixed a vulnerability in Dhcp. Due to an error, the patch to fix the vulnerability was not properly applied on Ubuntu 8.10 and higher. Even with the patch improperly applied, the default compiler options reduced the vulnerability to a denial of service. Additionally, in Ubuntu 9.04 and higher, users were also protected by the AppArmor dhclient3 profile. This update fixes the problem.

Original advisory details:

It was discovered that the DHCP client as included in dhcp3 did not verify
the length of certain option fields when processing a response from an IPv4
dhcp server. If a user running Ubuntu 6.06 LTS or 8.04 LTS connected to a
malicious dhcp server, a remote attacker could cause a denial of service or
execute arbitrary code as the user invoking the program, typically the
'dhcp' user. For users running Ubuntu 8.10 or 9.04, a remote attacker
should only be able to cause a denial of service in the DHCP client. In
Ubuntu 9.04, attackers would also be isolated by the AppArmor dhclient3
profile.