USN-5034-2: c-ares vulnerability

USN-5034-2: c-ares vulnerability

USN-5034-1 fixed a vulnerability in c-ares. This update provides
the corresponding update for Ubuntu 16.04 ESM.

Original advisory details:

Philipp Jeitner and Haya Shulman discovered that c-ares incorrectly
validated certain hostnames returned by DNS servers. A remote attacker
could possibly use this issue to perform Domain Hijacking attacks.
Source: USN-5034-2: c-ares vulnerability