A security issue affects the following Ubuntu releases:

=> Ubuntu 6.06 LTS
=> Ubuntu 7.04
=> Ubuntu 7.10
=> Ubuntu 8.04 LTS

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

Samba developers discovered that nmbd could be made to overrun a buffer during the processing of GETDC logon server requests.  When samba is configured as a Primary or Backup Domain Controller,  a remote attacker could send malicious logon requests and possibly cause a denial of service. (CVE-2007-4572) .

Alin Rad Pop of Secunia Research discovered that Samba did not properly perform bounds checking when parsing SMB replies.  A remote attacker could send crafted SMB packets and  execute arbitrary code. (CVE-2008-1105)

How do I fix this issue?
Login as root and type the following two commands:

$ sudo apt-get update
$ sudo apt-get upgrade