libssh vulnerabilities

USN-6592-1 fixed vulnerabilities in libssh. This update provides the
corresponding updates for Ubuntu 16.04 LTS and Ubuntu 18.04 LTS.

Original advisory details:

It was discovered that libssh incorrectly handled the ProxyCommand and the
ProxyJump features. A remote attacker could possibly use this issue to
inject malicious code into the command of the features mentioned through
the hostname parameter. (CVE-2023-6004)

It was discovered that libssh incorrectly handled return codes when
performing message digest operations. A remote attacker could possibly use
this issue to cause libssh to crash, obtain sensitive information, or
execute arbitrary code. (CVE-2023-6918)