Some things do not work when rhel8cis_crypto_policy is FUTURE

[bbaassssiiee]

https://github.com/ansible-lockdown/RHEL8-CIS/blob/49117ef490f6d6894804407a5b10ed43f8a68a50/defaults/main.yml#L425

Lot's of repositories and mirrors are signed by Let's Encrypt or GlobalSign, which use 2048 bits keys.

FIPS is a bit more secure than DEFAULT.

[uk-bolly]

Hi @bbaassssiiee

This is very true but fips is not without its own challenges. Like all benchmarks it does require the user to understand what impact each control has on their system and the way that it works for them. While DEFAULT is not ideal it is still more restrictive than LEGACY. Ideally though it should be greater as you have pointed out.

Thanks as always

uk-bolly

[Thulium-Drake]

There's a workaround for that (that's been sitting in my mailbox for over a year now, as I haven't needed it yet) that might be a good fit for in this role somewhere:

echo 'key_exchange = ECDHE RSA DHE DHE-RSA PSK DHE-PSK ECDHE-PSK ECDHE-GSS DHE-GSS' > /etc/crypto-policies/policies/modules/RSA-2048.pmod
echo 'min_rsa_size = 2048' >> /etc/crypto-policies/policies/modules/RSA-2048.pmod

update-crypto-policies --set FUTURE:RSA-2048

This will allow RSA keys with a length of 2048 bits, but still keep all the other policies in place.

However, I have no clue how useful that is (I don't know the details of the crypto policies, just that setting FUTURE seems to break a lot of things :-) )

[bbaassssiiee]

There's a workaround for that (that's been sitting in my mailbox for over a year now, as I haven't needed it yet) that might be a good fit for in this role somewhere:

echo 'key_exchange = ECDHE RSA DHE DHE-RSA PSK DHE-PSK ECDHE-PSK ECDHE-GSS DHE-GSS' > /etc/crypto-policies/policies/modules/RSA-2048.pmod
echo 'min_rsa_size = 2048' >> /etc/crypto-policies/policies/modules/RSA-2048.pmod

update-crypto-policies --set FUTURE:RSA-2048

This will allow RSA keys with a length of 2048 bits, but still keep all the other policies in place.

However, I have no clue how useful that is (I don't know the details of the crypto policies, just that setting FUTURE seems to break a lot of things :-) )

This can be implemented since https://github.com/ansible-lockdown/RHEL8-CIS/pull/297 was merged.

[bbaassssiiee]

The 3.0.0 version of the benchmark states:

Over-riding or opting out of the system-wide crypto policy could allow for
 the use of less secure Ciphers, MACs, KexAlgorithms and GSSAPIKexAlgorithm

Note: If changes to the system-wide crypto policy are required to meet local 
site policy for the openSSH server, these changes should be done with a sub-policy 
assigned to the system-wide crypto policy. For additional information see the 
CRYPTO-POLICIES(7) man page

So what you suggest is the way to go!

[uk-bolly]

hi @bbaassssiiee

Im hoping that this has now been addressed? Please feel free to close if this is the case.

Many thanks as always

uk-bolly

[bbaassssiiee]

hi @bbaassssiiee

Im hoping that this has now been addressed? Please feel free to close if this is the case.

I think we can close this if we move rhel8cis_allowed_crypto_policies_modules from vars to defaults, then sites can define their local policy modules, with their names in their project.

[bbaassssiiee]

A PMOD for better SSH security

# https://gitlab.com/redhat-crypto/fedora-crypto-policies

# message authentication code algorithms
# https://gitlab.com/redhat-crypto/fedora-crypto-policies/-/issues/48
mac@SSH = -*-64* -UMAC-128 -HMAC-SHA1
# SSH prioritizes the encrypt-then-MAC over encrypt-and-MAC algorithms.
ssh_etm = 1

# key exchange algorithms override FUTURE
key_exchange = ECDHE RSA DHE DHE-RSA PSK DHE-PSK ECDHE-PSK ECDHE-GSS DHE-GSS
# Disable weak DH groups and NIST curves, add EC
group@SSH = +X25519 +X448 -FFDHE-2048 -SECP256R1 -SECP384R1 -SECP521R1
# Disabled diffie-hellman-group-exchange-sha256, enable for CIS-CAT Pro audit tool
arbitrary_dh_groups = 0

hash = -SHA1
sign = -*-SHA1
sign@SSH = -*-SHA1 +EDDSA-ED25519
# Don't use this size for SSH keys.
min_rsa_size = 2048
min_dh_size = 3072

# encryption algorithms (ciphers)
cipher@SSH = -*-CBC -CHACHA20-POLY1305 +AES-192-CTR -AES*-GCM

ssh_certs = 1