USN-6560-2: OpenSSH vulnerabilities

USN-6560-1 fixed several vulnerabilities in OpenSSH. This update provides
the corresponding update for Ubuntu 16.04 LTS and Ubuntu 18.04 LTS.

Original advisory details:

Fabian Bäumer, Marcus Brinkmann, Jörg Schwenk discovered that the SSH
protocol was vulnerable to a prefix truncation attack. If a remote attacker
was able to intercept SSH communications, extension negotiation messages
could be truncated, possibly leading to certain algorithms and features
being downgraded. This issue is known as the Terrapin attack. This update
adds protocol extensions to …

advisory attack attacker communications extension fabian bäumer intercept jörg schwenk lts marcus marcus brinkmann messages negotiation openssh openssh vulnerabilities protocol ssh ssh communications ssh protocol truncated ubuntu update usn vulnerabilities vulnerable