Ubuntu 23.10 OpenSSH USN-6560-1 Critical: Protocol Attack Mitigation

A security issue affects these releases of Ubuntu and its derivatives: - Ubuntu 23.10 - Ubuntu 23.04 - Ubuntu 22.04 LTS - Ubuntu 20.04 LTS Summary: Several security issues were fixed in OpenSSH. Software Description: - openssh: secure shell (SSH) for secure access to remote machines 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) Luci Stanescu discovered that OpenSSH incorrectly added destination constraints when smartcard keys were added to ssh-agent, contrary to expectations. This issue only affected Ubuntu 22.04 LTS, and Ubuntu 23.04. (CVE-2023-28531)