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teamhephy / builder

MIT License
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chore(sshd): exclude deprecated SSHv2 key exchange algorithms #53

Closed pdomagala closed 4 years ago

pdomagala commented 4 years ago

According to: https://infosec.mozilla.org/guidelines/openssh#Configuration

kingdonb commented 4 years ago

We should also upgrade deis/base, per your suggestion... I can see that we have built a newer base, but it does not appear to be used in builder at least. This smaller patch looks a lot less likely to cause issues though, as that upgrade to base represents an upgrade between LTS releases of the underlying Ubuntu image, to 18.04.

Thanks for the contribution!

Cryptophobia commented 4 years ago

Also from the link you posted in mozzila.org:

Looks like we should list chacha20-poly before aes-gcm or others.

Ciphers and algorithms choice

    When CHACHA20 (OpenSSH 6.5+) is not available, AES-GCM (OpenSSH 6.1+) and any other algorithm using EtM (Encrypt then MAC) disclose the packet length - giving some information to the attacker. Only recent OpenSSH servers and client support CHACHA20.
    NIST curves (ecdh-sha2-nistp512,ecdh-sha2-nistp384,ecdh-sha2-nistp256) are listed for compatibility, but the use of curve25519 is generally preferred.
    SSH protocol 2 supports DH and ECDH key-exchange as well as forward secrecy. Regarding group sizes, please refer to Key management Guidelines.

The various algorithms supported by a particular OpenSSH version can be listed with the following commands:

$ ssh -Q cipher
$ ssh -Q cipher-auth
$ ssh -Q mac
$ ssh -Q kex
$ ssh -Q key

In our current deis-builder image these command yield the following:

$ ssh -Q cipher

3des-cbc
blowfish-cbc
cast128-cbc
arcfour
arcfour128
arcfour256
aes128-cbc
aes192-cbc
aes256-cbc
rijndael-cbc@lysator.liu.se
aes128-ctr
aes192-ctr
aes256-ctr
aes128-gcm@openssh.com
aes256-gcm@openssh.com
chacha20-poly1305@openssh.com
$ ssh -Q cipher-auth

aes128-gcm@openssh.com
aes256-gcm@openssh.com
chacha20-poly1305@openssh.com
$ ssh -Q mac

hmac-sha1
hmac-sha1-96
hmac-sha2-256
hmac-sha2-512
hmac-md5
hmac-md5-96
hmac-ripemd160
hmac-ripemd160@openssh.com
umac-64@openssh.com
umac-128@openssh.com
hmac-sha1-etm@openssh.com
hmac-sha1-96-etm@openssh.com
hmac-sha2-256-etm@openssh.com
hmac-sha2-512-etm@openssh.com
hmac-md5-etm@openssh.com
hmac-md5-96-etm@openssh.com
hmac-ripemd160-etm@openssh.com
umac-64-etm@openssh.com
umac-128-etm@openssh.com
ssh -Q kex
diffie-hellman-group1-sha1
diffie-hellman-group14-sha1
diffie-hellman-group-exchange-sha1
diffie-hellman-group-exchange-sha256
ecdh-sha2-nistp256
ecdh-sha2-nistp384
ecdh-sha2-nistp521
curve25519-sha256@libssh.org
$ ssh -Q key

ssh-ed25519
ssh-ed25519-cert-v01@openssh.com
ssh-rsa
ssh-dss
ecdsa-sha2-nistp256
ecdsa-sha2-nistp384
ecdsa-sha2-nistp521
ssh-rsa-cert-v01@openssh.com
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
$ sshd -v

OpenSSH_7.2p2 Ubuntu-4ubuntu2.8
...
Cryptophobia commented 4 years ago

@pdomagala , okay looks great! Sorry to bother you again but since we are here, one more single line change. Could we change the LogLevel on the sshd_config to Verbose. I read that this LogLevel logs the ssh key fingerprints for better auditing and is a nice security feature to have without compromising any security.

Line 9 should read:

LogLevel VERBOSE

https://www.ssh.com/ssh/sshd_config/#sec-Verbose-logging

pdomagala commented 4 years ago

@Cryptophobia done!