Ubuntu 18.04 LTS USN-6560-2 critical: OpenSSH protocol attack mitigation

A security issue affects these releases of Ubuntu and its derivatives: - Ubuntu 18.04 LTS (Available with Ubuntu Pro) - Ubuntu 16.04 LTS (Available with Ubuntu Pro) Summary: Several security issues were fixed in OpenSSH. Software Description: - openssh: secure shell (SSH) for secure access to remote machines Details: 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 mitigate this issue. (CVE-2023-48795) It was discovered that OpenSSH i...