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Ubuntu Security Notice USN-636-1 August 19, 2008
postfix vulnerability
CVE-2008-2936
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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.

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

Ubuntu 6.06 LTS:
postfix 2.2.10-1ubuntu0.2

Ubuntu 7.04:
postfix 2.3.8-2ubuntu0.2

Ubuntu 7.10:
postfix 2.4.5-3ubuntu1.2

Ubuntu 8.04 LTS:
postfix 2.5.1-2ubuntu1.1

In general, a standard system upgrade is sufficient to effect the necessary changes.

Details follow:

Sebastian Krahmer discovered that Postfix was not correctly handling mailbox ownership when dealing with Linux's implementation of hardlinking to symlinks. In certain mail spool configurations, a local attacker could exploit this to append data to arbitrary files as the root user.
The default Ubuntu configuration was not vulnerable.

thanks for posting the thread as i currenty using ubuntu 8.04 postfix on my production server..