RHEL/CentOS 8 requires removal or editing of /etc/crypto-policies/back-ends/openssh*.config

[Teknoenie]

Describe the bug
OpenSSH server configuration is handled by 'update-crypto-policy' which provides

/etc/crypto-policies/back-ends/openssh.config

and

/etc/crypto-policies/back-ends/opensshserver.config.bak

These files must be removed or altered in to function correctly.

Expected behavior
OpenSSH policies for Key Exchanges, MACs and Ciphers as defined by the Ansible module work.

Actual behavior
OpenSSH policies for Key Exchanges, MACs and Ciphers as defined by the Ansible module are ignored.

Example Playbook

- hosts: localhost
  roles:
    - ansible-ssh-hardening

  vars:
    ssh_moduli_minimum: 3071
    ssh_host_key_files: [ '/etc/ssh/ssh_host_ed25519_key' ]
    ssh_cipers: [ 'chacha20-poly1305@openssh.com',
                  'aes256-gcm@openssh.com',
                  'aes256-ctr',
                  'aes128-gcm@openssh.com',
                  'aes128-ctr' ]
    ssh_kex: [ 'curve25519-sha256',
               'curve25519-sha256@libssh.org',
               'diffie-hellman-group16-sha512',
               'diffie-hellman-group18-sha512' ]
    ssh_macs: [ 'hmac-sha2-512-etm@openssh.com',
               'hmac-sha2-256-etm@openssh.com',
               'umac-128-etm@openssh.com' ]

OS / Environment
CentOS Linux release 8.1.1911 (Core)

Ansible Version

ansible 2.9.7
  config file = None
  configured module search path = ['/root/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python3.6/site-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 3.6.8 (default, Nov 21 2019, 19:31:34) [GCC 8.3.1 20190507 (Red Hat 8.3.1-4)]

Role Version

- src: https://github.com/dev-sec/ansible-ssh-hardening.git

Additional context
None

[rndmh3ro]

Thanks for this, I did not know that this exists.

More information: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/security_hardening/using-the-system-wide-cryptographic-policies_security-hardening

We'll have to decide what to support and use.

[Teknoenie]

While not a bug, it would seem that the client configurations also don't disallow host key types for use. I'm not sure how to best accomplish this but it would be nice if we could also figure out how to enforce SSH client configuration for allowed HostKeyTypes.

'HostKeyAlgorithms' can (should 🤔 ) be defined to also limit client Host Key Types.

HostKeyAlgorithms -ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-dss-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-rsa,ssh-rsa-cert-v01@openssh.com

[schurzi]

The openssh-server side of this issue is fixed by #309.
This only leaves the client side issue remaining.

[schurzi]

the crypto policy for ssh client is activated by an include /etc/ssh/ssh_config.d/05-redhat.conf since our config does not have this include the client part should also be solved. Will check this in a moment.

[schurzi]

This is possible to check via ssh -G localhost |grep ciphers. We will add some tests for this to our baseline. So basically this is solved now, just waiting for the PR in ssh-baseline and then we should be safe :)

[schurzi]

just submittet a PR to our baseline (dev-sec/ssh-baseline#177)
I will close this now, since all issues are resolved.