Question

My SSH server is being attacked.

Asked by: ubuntuguy

Hi I have a FreeNAS server for which I only use SSH to connect remotely. I happened to put an error message online which contained the IP address for my machine. When I view at the logs I see hundreds of failed log in attempts.

I know SSH is secure, but should I be concerned? I'm getting too many attacks. What should I do?

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Asked On
2009-10-21 at 00:55:19ID24829646
Topics

Miscellaneous Security

,

SSH / Telnet Software

,

Networking Security Vulnerabilities

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Answers

 

by: Let_Me_BePosted on 2009-10-21 at 01:03:50ID: 25621562

That's absolutely normal. You don't even have to put your IP address somewhere, every accessible machine on the Internet receives these attempts. They are coming from botnets and are purely automatic and designed to guess most common login/password combinations to generate more zombies for the botnet.

 

by: TolomirPosted on 2009-10-21 at 01:19:24ID: 25621645

You might want to implement port nocking for your server:

http://en.wikipedia.org/wiki/Port_knocking

In computer networking, port knocking is a method of externally opening ports on a firewall by generating a connection attempt on a set of prespecified closed ports. Once a correct sequence of connection attempts is received, the firewall rules are dynamically modified to allow the host which sent the connection attempts to connect over specific port(s). A variant called Single Packet Authentication exists, where only a single 'knock' is needed, consisting of an encrypted packet.

There is an implementation for linux and ssh available.

Tolomir


 

by: KeremEPosted on 2009-10-21 at 01:26:30ID: 25621686

Hi,

When an IP address appears somewhere hackers are trying to penetrat the system usig port scanners once they find an active port an if it is a port like SSH they try hard to penetrte nto the systems.

Since this is a distro for NAS functionality it might not be updated as fast as the OS gets a patch for critical applications like SSH and since this is a specialied system I'll suggest you not to trust the security of SSH. I'll suggest you to block access to the SSH port and allow only fom the authorized hosts.

It might also be a good idea to change the de default 22 port to something non standard such as 2222 or similar.

I'd also suggest you to disable SSH aces by password and allow only private key access.

Cheers,
K.

 

 

by: jahboitePosted on 2009-10-22 at 04:07:51ID: 25632734

I agree with KeremE about non-default port, disabling password authentication in favour of SSH keys for authentication and I'd also add that it would be advisable to limit access to a single IP (yours obviously) using iptables if it's available.

Some more info: http://isc.sans.org/diary.html?storyid=7369&rss

 

by: poweredsPosted on 2009-10-22 at 11:27:44ID: 25637425

Hi ubuntuguy,

The easiest way to do is to use tcp wrapper on ssh on your freenas (host allow, host deny), thereby allowing only specific ip addresses and denying the rest.

http://www.ssh.com/support/documentation/online/ssh/adminguide/32/Configuring_SSH_Secure_Shell_for_TCP_Wrappers_Support.html

Hope this helps.

20120131-EE-VQP-002

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