openssh vulnerabilities

USN-8090-1 fixed vulnerabilities in OpenSSH. This update provides the
corresponding updates for Ubuntu 20.04 LTS.

Original advisory details:

Jeremy Brown discovered that the OpenSSH GSSAPI Key Exchange incorrectly
handled disconnecting clients. In non-default configurations where the
GSSAPIKeyExchange setting is enabled, a remote attacker could use this
issue to cause OpenSSH to crash, resulting in a denial of service, or
possibly execute arbitrary code. (CVE-2026-3497)

David Leadbeater discovered that OpenSSH incorrectly handled certain
control characters in usernames. When untrusted usernames and the
ProxyCommand are being used, an attacker could possibly use this issue to
execute arbitrary code. (CVE-2025-61984)

David Leadbeater discovered that OpenSSH incorrectly handled NULL
characters in ssh:// URIs. When the ProxyCommand is being used, an attacker
could possibly use this issue to execute arbitrary code. (CVE-2025-61985)