USN-6242-2: OpenSSH vulnerability

USN-6242-1 fixed a vulnerability in OpenSSH. This update provides
the corresponding update for Ubuntu 14.04 LTS, Ubuntu 16.04 LTS,
and Ubuntu 18.04 LTS.

Original advisory details:

It was discovered that OpenSSH incorrectly handled loading certain PKCS#11
providers. If a user forwarded their ssh-agent to an untrusted system, a
remote attacker could possibly use this issue to load arbitrary libraries
from the user's system and execute arbitrary code.

advisory agent issue lts openssh ssh ssh-agent system ubuntu untrusted update usn vulnerability