USN-918-1

A security issue affects the following Ubuntu releases:

Ubuntu 6.06 LTS
Ubuntu 8.04 LTS
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 6.06 LTS:
samba 3.0.22-1ubuntu3.11

Ubuntu 8.04 LTS:
samba 3.0.28a-1ubuntu4.11

Ubuntu 8.10:
samba 2:3.2.3-1ubuntu3.8

Ubuntu 9.04:
samba 2:3.3.2-1ubuntu3.4

Ubuntu 9.10:
samba 2:3.4.0-3ubuntu5.6

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

ATTENTION: This update changes the default samba behaviour. For security
reasons, it is no longer possible to use wide links and UNIX extensions at
the same time. After applying this security update, wide links will be
disabled automatically as UNIX extensions are turned on by default. If
wide links are required, you can re-enable them by adding
"unix extensions = no" to the [global] section of the /etc/samba/smb.conf
configuration file.

Details follow:

It was discovered the Samba handled symlinks in an unexpected way when both
"wide links" and "UNIX extensions" were enabled, which is the default. A
remote attacker could create symlinks and access arbitrary files from the
server.