[CentOS] Security advice, please

JohnS jses27 at gmail.com
Mon Mar 23 17:57:45 UTC 2009


On Mon, 2009-03-23 at 16:26 +0000, Anne Wilson wrote:
> On Monday 23 March 2009 15:29:53 JohnS wrote:
> > On Mon, 2009-03-23 at 14:31 +0000, Anne Wilson wrote:
> > > On Tuesday 23 December 2008 15:38:17 Warren Young wrote:
> > > > Michael Simpson wrote:
> > > > >> GRC reports that ports are stealthed
> > > > >
> > > > > Try www.auditmypc.com or nmap-online.com rather than grc to look for
> > > > > open ports
> > > >
> > > > What advantages do they have, in your opinion?
> > > >
> > > > >> there a better way than opening port 143?
> > > > >
> > > > > ssh tunnelling?
> > > >
> > > > I agree, though the default CentOS sshd configuration requires some
> > > > tightening down to trust it on Internet-facing servers, IMHO:
> > > >
> > > > 1. In /etc/ssh/sshd_config, set "PasswordAuthentication no".  No matter
> > > > how good your password, it isn't as good as using keys.  Remember,
> > > > forwarding ssh opens it to pounding 24x7 from any of the millions on
> > > > zombie boxes on the Internet.
> > > >
> > > > 2. On the machine(s) that you want to allow logins from, run
> > > > "ssh-keygen -t rsa" to generate a key pair, if you haven't already. 
> > > > Then copy the contents of ~/.ssh/id-rsa.pub into ~/.ssh/authorized_keys
> > > > on your home server.  These keys are used to authenticate the remote
> > > > system, in lieu of a password or physical token.  You could put these
> > > > keys on a USB stick instead, if you didn't want to keep them
> > > > permanently on the remote hosts.
> > > >
> > > > 3. Disable SSHv1 protocol support in /etc/ssh/sshd_config: "Protocol
> > > > 2", not "Protocol 2,1".  SSHv1 has known weaknesses.  Boggles my mind
> > > > that it's still enabled by default....
> > > >
> > > > 4. Same file, set "PermitRootLogin no" if it isn't already.
> > > >
> > > > (Aside: I also like to set up sudo with one account allowed to do
> > > > anything, then lock the root account, so the only way to get root
> > > > access is to log in as a regular user then sudo up, reducing the risk
> > > > of passwordless keys.)
> > > >
> > > > Having done all this, you're ready to allow remote access:
> > > >
> > > > 5. In your router, forward a high-numbered port to 22 on the server. 
> > > > If it's not smart enough to use different port numbers on either side,
> > > > you can change the sshd configuration so it listens on a different port
> > > > instead.  I like to use 22022 for this.
> > > >
> > > > This is *not* security through obscurity.  It's simply a way to reduce
> > > > the amount of log spam you have to dig through when monitoring your
> > > > system's behavior.  Everything that appears in your logs should be
> > > > *interesting*.  Constant port knocking from worms and script kiddies is
> > > > not interesting.
> > > >
> > > > In case you've not done ssh tunelling, Anne, the command that does what
> > > > you want, having done all the above is:
> > > >
> > > > 	$ ssh -p22022 -L10143:my.server.com:143 anne at my.server.com
> > > >
> > > > This sets up port 10143 on the local system to be redirected through
> > > > the ssh session to the IMAP port on your home server.  You don't want
> > > > to redirect 143 to 143 because that would require you to run ssh as
> > > > root. It also prevents you from using this on a system that itself has
> > > > an IMAP server.
> > > >
> > > > With the tunnel up, you can set up your mail client to connect to port
> > > > 10143 on localhost, and you'll be looking at your remote mail server.
> > >
> > > Hello again.  You were kind enough to give me this advice last December. 
> > > I've another holiday approaching and thought it was time that I got this
> > > sorted. Unfortunately, I'm not sure that I can do this, so I'm asking
> > > your opinion.
> > >
> > > My router is a Netgear DG834G.  I can create a service, tell it which
> > > ports to open, and say which local IP I want it sent to.  However, I
> > > can't see any way to set the port to which it should be forwarded as
> > > anything other than the incoming port.  IOW, I can enable the new service
> > > Ext-ssh, which accepts incoming traffic on port 22022, and direct it to
> > > my server on 192.168.0.40, but I can't see how to make it send that
> > > traffic to port 22 on the server.
> > >
> > > Am I totally misunderstanding this?  Really all I want is to be able to
> > > log in to the server if I get an email alert that there is a problem or
> > > security updates pending.  If I can get this sorted, I'll look again at
> > > how to route the IMAP mail through the tunnel too.
> >
> > ---
> > http://kbserver.netgear.com/kb_web_files/n101145.asp
> > http://kbserver.netgear.com/kb_web_files/n101145.asp#FR114PAnchor
> >
> Sure, but those pages are very much like the router's doc pages.  I don't see 
> any info about forwarding to ports different from the incoming one.
---
Her's another example it will do what you want, your just
misunderstanding it. I have 2 customers that use Netgear routers. I
think your not setting up the Nat - Add Page.
http://portforward.com/english/routers/port_forwarding/Netgear/DG834G/eMule.htm
One thing are you using it for the DSL or another modem/router for dsl?
If your using two only one can be Natted and the other Main router in
Bridged Mode.
JohnStanley



More information about the CentOS mailing list