Difference between revisions of "Category:SSH"

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(sshd_conf tweaks)
(sshd_conf tweaks)
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# this speeds up logins.
 
# this speeds up logins.
 
UseDNS no
 
UseDNS no
# This actually means two -- the initial try plus 1 more.
+
# Don't make this 1. Public keys count as 1 try. If that fails it will not try password.
MaxAuthTries 1
+
MaxAuthTries 2
 
# bots often check these accounts for weak passwords:
 
# bots often check these accounts for weak passwords:
 
DenyUsers root test admin guest nobody
 
DenyUsers root test admin guest nobody

Revision as of 13:37, 5 November 2007


External OpenSSL Command-line FAQ

This OpenSSL HowTo/FAQ deals with the command-line openssl.

sshd_conf tweaks

These are changes I always make to /etc/ssh/sshd_config. See fail2ban for protecting against bots doing dictionary attacks.

# this speeds up logins.
UseDNS no
# Don't make this 1. Public keys count as 1 try. If that fails it will not try password.
MaxAuthTries 2
# bots often check these accounts for weak passwords:
DenyUsers root test admin guest nobody
# for extra security, limit access to only these users:
AllowUsers user1 user2 user3

Use the following to support SSH1. I no longer use this.

# this is required if you want to support SSH1
Protocol 2,1
# this is required if you want to support SSH1
PasswordAuthentication yes

simple port forwarding (SSH tunnel)

This example creates a tunnel for IMAP. Here we forward port 1143 on localhost to 143 (IMAP) on imap.example.com.

ssh -f -N -q -L 1143:localhost:143 username@imap.example.com

-f tells ssh to go into the background (daemonize).

-N tells ssh that you don't want to run a remote command. That is, you only want to forward ports.

-q tells ssh to be quiet

-L specifies the port forwarding

port forwarding through an intermediary

You can have the remote machine forward ports to a third machine. This is useful where your have your local machine outside a firewall; a visible machine on the DMZ; and a third machine invisible to the outside.

ssh -f -N -q -L 1143:192.168.1.100:143 username@dmz.example.com

Remote Server Security Enhancement with SSH Keys

You can make port forwarding even more secure by limiting what a privileged account can do. When you add a key to authorized_key you may pass parameters to fine tune the connection. This can be used to restrict what the client is allowed to do. On the remote server, add the following to ~username/.ssh/authorized_keys:

from="192.168.1.69",command="/bin/false",no-pty,no-X11-forwarding,no-agent-forwarding,no-port-forwarding,permitopen="localhost:143"
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA8XIr8LEXdvc4VZEvNenWkJrerTzNhqTT7QvCD+Y2EjCUPQwfBcSnvhY3oasNigNonghQFqm7/HqWBLpcN+4mqDUrXrEdj6HQmHvCV6WozNUVb5jjiyQ/JF4hqcQd6oelCkVw8wD32I2jlYqydpqOGY4xqakWDAfm3SOx5il3Kl49mKCg5B3GQPexhTujaTT3y/Q1eeT3zGpHE9Mp7k20X8rMxSjp5ncLAmdf42fRh05HY5f1GrupQIEdi0/TDcPNWL1ml89zttrDOLgDnwny7P0x2jmcX41cSxL/8svER7BAk2sroyQe6L21pJ7o2MYz1IwnsQgji/GjJoaA7hTNCQ== username@client.example.com
  • from="192.168.1.69": accept connection only from the given IP address
  • command="/bin/false": forces this command to be run no matter what is passed via ssh from the client
  • no-pty: never allocate a PTY for interactivity
  • no-X11-forwarding: No X11
  • no-agent-forwarding: we don't want or need ssh-agent
  • no-port-forwarding: prevent ssh -R ...
  • permitopen="localhost:143": allow only localhost connections to port 143 for `ssh -L` requests

reverse port forwarding

Sometimes I need to make an internal LAN machine expose a service to the outside WAN. For example, I have a database server that will only accept connections from a specific development box. That dev box is inside the firewall. I want to connect to the database from outside the firewall.

ssh -t -L 5432:localhost:1999 my_name@firewall.example.com ssh -t db_server ssh -t -R 1999:127.0.0.1:5432 my_name@firewall


SSH for Windows

Putty is the best free SSH client for Windows. You can also use Cygwin, but the ANSI terminal emulation isn't as good unless you start the X11 server and run xterm.

MindTerm SSH client Java Applet

MindTerm_2.1 (non-commercial). This was the last free version of MindTerm.

   mindterm.jar

Put this applet on a web page and point the <applet> "archive" attribute to the URL of the JAR file:

 <applet archive="mindterm.jar" code="com.mindbright.application.MindTerm.class" width="580" height="400"> 
     <param name="te" value="xterm-color"> <!-- "vt102" -->
     <param name="fs" value="18">
     <param name="gm" value="80x32+0+0">
     <param name="port" value="22">
     <param name="cipher" value="blowfish"> <!-- "des" -->
     <param name="usrname" value="">
     <param name="sepframe" value="false">
     <param name="quiet" value="false">
     <param name="cmdsh" value="false">
     <param name="verbose" value="true">
     <pa ram name="autoprops" value="none">
     <param name="idhost" value="false">
     <param name="alive" value="10">
     <param name="appletbg" value="white">
 </applet>

Subcategories

This category has only the following subcategory.

S

Pages in category "SSH"

The following 7 pages are in this category, out of 7 total.