RE: brute force attack - tcp wrappers andiptables not helping?

A few questions/comments inline below.

[email protected] giac 

> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Susanne Hemker
> Sent: Tuesday, April 26, 2005 8:08 AM
> To: [email protected]
> Subject: RE: [Intrusions] brute force attack - tcp wrappers 
> andiptables not helping?
> 
> 
> Hi everybody,
> thanks for your suggestions and sorry I did not get back to 
> you earlier. 
> 1) I tried to ssh from a host that is not on in my 
> /etc/hosts.allow and I do not get an ssh login, only : 
> ssh_exchange_identification: Connection closed by remote host. 

Which means you completed a tcp 3 way handshake but were refused by the
sshd ( probably tcp wrappers not ip tables)!
ip tables should have refused the connection before the threeway
handshake was completed.

> 2) The attacks come from different machines, some in Asia and 
> some in the U.S., but those look to me as if they were hacked 
> already in and are used to attack other computers. None of 
> those IPs are in any way allowed to log onto my workstation. 

What are those IPs and what does your dns resolver return when you ask
for a reverse ip lookup?
With all the dns poisoning, hijacking etc there may be a way to trick
your filters depending on the return hostname for that reverse ip
lookup.


> 3) In the Iptables I have everything from the outside set to 
> REJECT (both IPv4 and IPv6).
> 4) My "inside" hosts are on two subnets and those are listed 
> in the /etc/hosts.allow and set to" ACCEPT all" in the Iptables
> 5) I do not have the hosts listed in the sshd_config, perhaps 
> I should change this and also change the authentication 
> method (which is PasswordAuthentication right now) Any 
> further suggestions on how they might have gotten to the 
> ssh-login? Thanks, Susanne
>  
> >>> [email protected] 04/22/05 9:38 AM >>>
> Susanne, I see your concern.  Properly configured IPTables 
> rules and TCPWrappers should prevent this.  Have you actually 
> attempted to access the ssh service from a host outside of 
> the lab yourself?
> 
> Tim Walraven,CISSP,CISM,CISA
> Counterpane Internet Security
> 
> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Susanne Hemker
> Sent: Thursday, April 21, 2005 10:24 AM
> To: [email protected] 
> Subject: [Intrusions] brute force attack - tcp wrappers and 
> iptables nothelping?
> 
> Hi everybody,
> 
> somebody is trying to break into one of out workstations. 
> The /var/log/secure contains lots of:
> 
>  Failed password for invalid user $name  from ::ffff:$IP  
> port $port ssh2
> 
> from different IPs, ports and usernames.
> 
> Since the tcp wrappers and the iptables should not allow ssh 
> login from
> 
> any host outside our lab, I am wondering how he/she even got to the 
> login. Any suggestions?
> 
> Thanks,
> 
> Susanne
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