The problem can be corrected by upgrading the affected package to
version 2.0.2-4ubuntu2.1 (for Ubuntu 4.10), or 2.0.13-1ubuntu0.1 (for
Ubuntu 5.04). In general, a standard system upgrade is sufficient to
effect the necessary changes.
A firewall bypass vulnerability has been found in shorewall. If
MACLIST_TTL was set to a value greater than 0 or MACLIST_DISPOSITION
was set to "ACCEPT" in /etc/shorewall/shorewall.conf, and a client was
positively identified through its MAC address, that client bypassed
all other policies/rules in place. This could allow external computers
to get access to ports that are intended to be restricted by the
Please note that this does not affect the default configuration, which
does not enable MAC based client identification.