transport.py in the SSH server implementation of Paramiko before 1.17.6, 1.18.x before 1.18.5, 2.0.x before 2.0.8, 2.1.x before 2.1.5, 2.2.x before 2.2.3, 2.3.x before 2.3.2, and 2.4.x before 2.4.1 does not properly check whether authentication is completed before processing other requests, as demonstrated by channel-open. A customized SSH client can simply skip the authentication step.
https://www.exploit-db.com/exploits/45712/
https://usn.ubuntu.com/3603-2/
https://usn.ubuntu.com/3603-1/
https://lists.debian.org/debian-lts-announce/2021/12/msg00025.html
https://lists.debian.org/debian-lts-announce/2018/10/msg00018.html
https://github.com/paramiko/paramiko/issues/1175
https://github.com/paramiko/paramiko/commit/fa29bd8446c8eab237f5187d28787727b4610516
https://github.com/paramiko/paramiko/blob/master/sites/www/changelog.rst
https://access.redhat.com/errata/RHSA-2018:1972
https://access.redhat.com/errata/RHSA-2018:1525
https://access.redhat.com/errata/RHSA-2018:1328
https://access.redhat.com/errata/RHSA-2018:1274
https://access.redhat.com/errata/RHSA-2018:1213
https://access.redhat.com/errata/RHSA-2018:1125
https://access.redhat.com/errata/RHSA-2018:1124
https://access.redhat.com/errata/RHSA-2018:0646