Hello,

I have a PCIDSS environment where I need to:

1. restrict normal users to SFTP/SCP. This is easy done by setting the account to /sbin/nologin.
2. prevent root/admin users from gaining shell access outside of certain IP block. In other words, these users have to VPN in to gain shell access.

I don't have the ability to restrict by IP address at the firewall layer unfortunately. Any ideas here?

See AllowUsers in sshd_config(5), and the accompanying PATTERNS section in ssh_config(5). Together, they allow you to whitelist account@subnet, account@other-subnet, etc.

All else is denied by default. An alternative to this would be using pam_access(8) to whitelist an entire group@subnet. (We need to know what OS / version you're using in order to help further.)

2 members found this post helpful.

Oh fail on my part. I didn't realize I could white a user@subnet pattern. Let me chew on that. It's RHEL6.

If I'm understanding what you're saying correctly, you should be able to use the AllowUsers (or DenyUsers) parameters in sshd_config would be what you're after.

Set it up something like:
...so root could only log in from the 10.11.12 network, and be denied if they're coming in on the 192.* network. Which, if they're VPN'ed in, I'm assuming their subnet will be identifiable, and able to be put in here. You can even allow/deny to ONE address itself.

EDIT: Dangit, I was typing when the other two replies came in.

1 members found this post helpful.

I could go RTFM but just for fun conversation, just by doing DenyUser root@192.168.* without an explicit AllowUsers root@* will root still be able to login say from 172.16.5.20?

@td3201: I'd expect it to, but am not sure. That's one of those scenarios that is best to personally test and observe.

Again, if you find that sshd(8)'s allow/deny pattern directives are not quite meeting your needs, be sure to consider pam_access(8). It offers a little more flexibility, IMO.

I ended up going with pam_access on this for now but I may have a gap here.

1. No changes to sshd_config other than PermitRootLogin = no
2. /etc/security/access.conf looks like this (DOMAIN\foo is a Active Directory group):
+:DOMAIN\foo:10.
-:DOMAIN\foo:ALL

This works pretty well but anyone part of the domain outside of DOMAIN\foo can login. I need to be able to allow local users to login. Naturally, I can add them to a group and then put them in access.conf but I would prefer to just exclude any other domain logins such as this:
-:*\*:ALL

This doesn't work. Any other ideas?

Actually, thinking about this further. I want to explicitly require that users be added to a specific group for SFTP access so I ended up with this (sftp is a local group):

+OMAIN\foo,sftp:10
-:ALL:ALL


Resolved.