I have a monitoring server that requires the SSH connection details of a non-sudo user account of each box it monitors. Is there a way that I can configure a specific user account such that it can only be logged into from a specific IP (or better yet hostname)? I do not want to restrict the ability of other users on the server to be able to connect from other addresses (otherwise I'd just use a firewall), or use password authentication for the monitoring service only.
4 Answers
See man sshd_config
. There is possibility to add AllowUsers
block where you can specify both user and host like this:
AllowUsers user@host # or IP
Of course you need to specify also other users you want to allow login from, if you have some.
Another solution (depends on bug fixes!)
As I think about it once more, there is possibility to modify your sshd_config
like this:
Match Host !hostname
DenyUsers user
Match Host hostname
AllowUsers user
This would easily block all users except from user
from hostname
and from everywhere else it would block user
.
BUT it doesn't work, because of few bugs reported upstream [1] [2]. But we got it promised it will get fixed in next release.
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I did see that but was hoping there was a way I didn't have to specify all the other user accounts. I take it there is nothing like order of specificity where I could specify allow all users from any IP, and then that line, which resulted in that user only being allowed from that IP? Jul 18, 2015 at 8:45
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Would that require me to add all the other users in the system to a group? Could I not use DenyUser [user], then afterwards
AllowUser [user]@host
to override for that one host? Jul 18, 2015 at 8:54 -
Looks like I can't do exactly what I want so I need to either specify all users I allow, or go down the route of using keys for all logins, but permit password for only that one IP and have the monitoring server run on passwords. Jul 18, 2015 at 9:13
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1sorry. My bad. This won't work since Deny is evaluated before Allow. Maybe somebody can make up some solution, but I think it is not possible to solve it easily without fixing above mentioned bugs.– JakujeJul 19, 2015 at 9:21
You can use wildcards for the AllowUsers line on the /etc/ssh/sshd_config
file. So it would be feasible to add the line:
AllowUsers *@192.168.1.100
Or:
AllowUsers *@hostname
To allow everyone from that IP address or hostname access.
Remember to:
service ssh restart
Once you've made the changes, so long as you're on a version before 15.04. 15.04 uses systemd now, so has a different mechanism for controlling services.
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Thanks but this would prevent the other users from connecting from IPs other than 192.168.1.100 right? I'm trying to only restrict this one user to signing in from one IP and whatever I do must not effect other users in any way. Jul 18, 2015 at 14:39
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It can be used for a space seperated list, or with the @ symbol directly in front of group names. It's very configurable, but alternatively use a mix of some key based authentication without passwords for the servers, and normal password ssh for users. Sounds like that's already your plan though! Jul 18, 2015 at 17:19
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There's not a wildcard for all except a specified user such as regex ^(?!username$).* is there? Jul 18, 2015 at 17:27
According to man pages, this should work:
DenyUsers user@"!host,*"
I tested this on Debian and it seemed to work correctly.
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3See "PATTERNS" section here: manpages.ubuntu.com/manpages/precise/en/man5/ssh_config.5.html Deny connection if the
user
comes from this list of hosts:"!1.2.3.4,*"
. This list contains every host (*
) except 1.2.3.4 (!1.2.3.4
). Nov 27, 2018 at 10:58
Since this is the top search result in google, I think people should also be aware of setting permissions in the /etc/hosts.allow
file (curtesy of Cameron Oltmann's blog post on the matter):
To limit ssh access to a linux box based on originating IP address, edit /etc/hosts.allow:
sshd : localhost : allow sshd : 192.168.0. : allow sshd : 99.151.250.7 : allow sshd : mydomain.net : allow sshd : ALL : deny
The above entry will allow ssh access from localhost, the 192.168.0.x subnet, the single IP address 99.151.250.7, and mydomain.net (assuming mydomain.net has a ptr record in place to facilitate reverse lookup). All other IP addresses will be denied access to sshd.
Notes: You can allow or deny based on ip address, subnet, or hostname. List rules in order of most to least specific. The file only gets read until a matching line is found, so if you start with ssdh : ALL : deny, no ssh connections will be allowed.
And you should be able to use user@address
in this file, per this lifewire.com link:
The more complex forms daemon@host and user@host are explained in the sections on server endpoint patterns and on client username lookups, respectively.