USN-6560-1: OpenSSH vulnerabilities

Ubuntu Security Advisory

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.