dpkg vulnerability

USN-5446-1 fixed a vulnerability in dpkg. This update provides
the corresponding update for Ubuntu 16.04 ESM.

Original advisory details:

Max Justicz discovered that dpkg incorrectly handled unpacking certain
source packages. If a user or an automated system were tricked into
unpacking a specially crafted source package, a remote attacker could
modify files outside the target unpack directory, leading to a denial of
service or potentially gaining access to the system.