Download ppt - Phil Hurvitz [email protected] [email protected] Securing UNIX Servers with the Secure

Phil Hurvitz [email protected] http://[email protected] http://www.nwgeospatial.com

Securing UNIX Servers with the Secure Shell (ssh)

1

• What does any of this have to do with GIS?!

• What this paper is (and is not)

• Who this paper is for (and is not)

• The Secure Shell (ssh)

General Overview



2

• Many organizations, most notably those needing

“industrial strength” GIS, still use UNIX

• Many components of the Network still rely on UNIX servers

What does any of this have to do with GIS?!



3

• An introduction to securing UNIX servers, clients, and

networks with the Secure Shell (ssh)

• A description of typical ssh setup

• An overview of some sample Windows ssh clients

What this paper is



4

• A general discussion of UNIX security

• A detailed introduction to all of ssh functionality

(for details, see http://www.ssh.com)

What this paper is not



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• Anyone administering UNIX servers

• Anyone using UNIX servers who is concerned about security

Who this paper is for



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• UNIX security experts

• People not using UNIX as “active” clients or servers

• People using UNIX only as anonymous ftp or http servers

Who this paper is not for



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• Why use ssh?

• What is ssh?

• How does ssh work?

• Setting up ssh

• Running the ssh as a process on the UNIX server

• User setup (Key generation)

• Tunneling other services through ssh

• Windows ssh Clients

Detailed Overview



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• Out-of-the-box UNIX networking is inherently insecure

Why Use ssh?

INSECURE !

INSECURE !



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Why Use ssh?

INSECURE !

INSECURE !



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Why Use ssh?

INSECURE !

INSECURE !



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Why Use ssh?

INSECURE !

INSECURE !



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• Why is out-of-the-box UNIX networking inherently insecure?

• User-IDs and Passwords are sent across the wire in CLEAR TEXT!

Why Use ssh?



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request for login, X, or file services

service “wakes up”

Client (UNIX, Wintel) Server (UNIX)

request for user-idrequest for password

service offersauthentication challenge

client responds withuser-id & password

user-id and password sent

across wire in clear text

server authenticatesand provides service

client uses service

Out-of-the-box UNIX Networking



14

• Any UNIX machine on the subnet can log user-ids and

passwords from ftp or telnet sessions

• Use of snoop, sniffit, snort, or other packet sniffers

How Insecure is Telnet or ftp?

linux machine running snoop as root

subnet



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phurvitz

12345671017192552

password: *******



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space:~tmp/log:172# snoop -i snoop.out

23 0.00026 badass -> lobo TELNET R port=34844 login: 25 1.70087 lobo -> badass TELNET C port=34844 p 28 0.25049 lobo -> badass TELNET C port=34844 h 30 0.03874 lobo -> badass TELNET C port=34844 u 33 0.02809 lobo -> badass TELNET C port=34844 r 36 0.17347 lobo -> badass TELNET C port=34844 v 39 0.06427 lobo -> badass TELNET C port=34844 i 42 0.06775 lobo -> badass TELNET C port=34844 t 45 0.16108 lobo -> badass TELNET C port=34844 z 50 0.04550 lobo -> badass TELNET C port=34844 51 0.00027 badass -> lobo TELNET R port=34844 Password: 53 1.06545 lobo -> badass TELNET C port=34844 f 55 0.20479 lobo -> badass TELNET C port=34844 u 57 0.13032 lobo -> badass TELNET C port=34844 c 59 0.41778 lobo -> badass TELNET C port=34844 k 61 0.19929 lobo -> badass TELNET C port=34844 m 63 0.04144 lobo -> badass TELNET C port=34844 e 65 0.95020 lobo -> badass TELNET C port=34844 ! 75 0.13021 badass -> lobo TELNET R port=34844 Login incorrect\r\n



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space:~tmp/log:172# snoop -i snoop.out

1 0.00000 lobo -> badass FTP C port=34851 2 0.00046 badass -> lobo FTP R port=34851 3 0.00039 lobo -> badass FTP C port=34851 8 0.10195 badass -> lobo FTP R port=34851 220 wa-node FTP serv 9 0.00034 lobo -> badass FTP C port=34851 10 2.47434 lobo -> badass FTP C port=34851 USER phurvitz\r\n 11 0.00025 badass -> lobo FTP R port=34851 12 0.01501 badass -> lobo FTP R port=34851 331 Password require 13 0.04388 lobo -> badass FTP C port=34851 17 4.49758 lobo -> badass FTP C port=34851 PASS oh-shit\r\n



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• A method to avoid passing clear text user-ids &

passwords

• A method of using strong (e.g., 1024 bit)

encryption for user authentication

• A replacement for telnet, rsh, rlogin, rcp

• A method of encrypting arbitrary TCP/IP data

transmissions (e.g., X11, ftp, Z39.50)

What is ssh?



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• Uses public key encryption

• Encryption key is public, but decryption key is private

• User-ids and passwords are never passed in clear text

How Does ssh Work?



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request for login, X,or file services

ssh service “wakes up”

Client (UNIX, Wintel) Server (UNIX)

request for user-idrequest for passphrase

ssh service offersauthentication challenge

client responds withuser-id & passphrase

user-id and passphrase sent

across wire 1024-bit encrypted

passphrase and public key arecompared against private key

client uses service; subsequentcommunication is encrypted

ssh UNIX Networking



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• Download

• Compile

• Enable ssh1 compatibility

Setting Up ssh



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• Visit www.ssh.com or mirror

• Get latest ssh1 and ssh2 server/client tarballs

• Get latest Windows ssh client

Downloading ssh



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• Compile ssh1

• Compile ssh2

Setting Up ssh

root@badass 175# ./configure --with-xloading cache ./config.cachechecking distribution consistency... donechecking host system type... sparc-sun-solaris2.7...

root@badass 176# makemake all-recursiveMaking all in libMaking all in sshutilMaking all in sshcoreMaking all in sshadt...

root@badass 176# make install...



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• Enable ssh1

compatibility

Setting Up ssh

root@badass 120# grep -i ssh1 ssh2_config ...Ssh1Compatibility yesSsh1Path /usr/local/bin/ssh1...

root@badass 121# grep -i ssh1 sshd2_config ...Ssh1Compatibility yesSshd1Path /usr/local/bin/ssh1...



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• Set up as daemon to start at boot or

• Set up as inetd process

• “Encase” in TCP Wrappers

Running ssh as a process on the UNIX server



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• Create/copy an existing startup script in /etc/init.d

• Create a symlink to S... and K... scripts in /etc/rc3.d

• Start the sshd daemon

• The sshd daemon will respond to incoming ssh requests

• sshd will offer an authentication challenge across an encrypted channel

• sshd will spawn a new shell, but across an encrypted channel

Setting Up ssh as a Daemon



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• Alter the /etc/inet/inetd.conf file:

ssh stream tcp nowait root \

/usr/local/sbin/sshd sshd -I

• Alter the /etc/inet/services file:

ssh 22/tcp

• Restart the inetd daemon

• A new ssh process will start for each client request

Setting Up ssh as an inetd Process



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• Compile with TCP Wrapper support./configure \--with-libwrap=/usr/local/lib/libwrap.a

• Alter Makefile-I/PATHOF/tcpwrappersWRAPLIBS = -L/PATHOF/tcpwrappers -lwrap

• Alter /etc/hosts.allow and /etc/hosts.deny

• Run ssh2 as a daemon

• Connections will be logged to /var/log/syslog

“Encasing” ssh in TCP Wrappers



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• Create key pairs

• Set up important authorization files

• Copy public keys to remote hosts

User Setup



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• ssh-keygen and/or ssh-keygen2

(creates private key and public key)

• Only owner has private key

• Public key is available to anyone

• Data are encrypted with public key

• Decryption is possible only with the private key

• Private key is encrypted with the passphrase in case of file

system security breach

Create key pairs



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• copy all personal public keys to ~/.ssh/authorized_keys

Setup of Authorization Files under ssh1



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• edit a few important files in ~/.ssh2

Setup of Authorization Files under ssh2



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Tunneling Other Services Through ssh

ssh

MS or UNIX

client

UNIX

server

tcp tcptcptcptcp tcptcptcp tcptcptcp tcp

sniffer

x network is “shielded” by ssh



34

• Native X11 is an insecure channel, however, ...

• X11 can be tunneled through ssh

• X11 forwarding must be compiled in (default)

• DISPLAY variable should not be set manually

• New DISPLAY variable will be “host:X.0” (where X > 0)

• X11 displays will forward from host to client through ssh

• If local X server is running (e.g., eXceed), X displays are

automatically forwarded to PC

• X11 tunneling is default behavior if X11 support is compiled in

ssh +x host

Tunneling X11 Through ssh



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UNIX client

• Set up a forwarded port

myhost% ssh -L 1234:host:21 host

myhost% ftp localhost 1234

• ftp transmissions take place through encrypted channel

Windows client

• Use client’s tcp forwarding (discussed later for each Windows client)

Tunneling ftp Through ssh



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• TeraTerm

• MindTerm

• SSH Secure Shell

• Others exist ...

http://www.slurping.com/ssh.html

Windows ssh Clients



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• Free telnet & ssh1 client

• Uses ssh1 protocol

• Can tunnel services (e.g., X11, ftp)

• Basic TeraTerm:

http://hp.vector.co.jp/authors/VA002416/teraterm.html

• TeraTerm with ssh:

http://www.zipworld.com.au/~roca/ttssh.html

TeraTerm



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TeraTerm with ssh

ssh support

functionality is just like any basic telnet



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TeraTerm Port Forwarding

automatic X11 forwarding



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MindTerm

• Free telnet-like ssh1 client

• Written entirely in Java ( => can be made into a Web client)

• Uses ssh1 protocol


• Built-in scp1 (secure copy)

• Download:

http://www.mindbright.se

• Needs Java client on PC

http://www.sun.com/software/solaris/java/download.html



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MindTerm



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MindTerm ftp Tunneling

indicate local port to use

indicate remote port forforwarding

indicate remote hostindicate protocol



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MindTerm scp (secure copy)

copy from

copy to

recursive to copyentire directories

progress indication

secure copy of files across ssh-encrypted channel



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SSH Secure Shell

• Free (for non-profit) telnet-like ssh2 client

• Uses ssh2 protocol only (more secure)

• Built-in graphical scp2


• Download:

http://www.ssh.com



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SSH Secure Shell



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SSH Secure Shell X11 forwarding



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SSH Secure Shell ftp (or other port) forwarding



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local file system

drag-and-drop to host

ssh host file system

SSH Secure Shell scp



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ssh ftp Forwarding

• Create an ssh local port redirection to the ftp port on remote host

• Use Windows ftp client

• Connect to localhost (127.0.0.1)

• Use local port from redirection (e.g. 1200)

• Use Passive Mode



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ssh ftp Forwarding



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Conclusion

• As the Internet grows in size and number of users, expect security to

become more of an issue

• Using ssh can greatly increase the security of your network

• Using ssh is fairly straightforward

• Cost-to-benefit ratio for security is high; software is free, the only

cost is administrator and user time & effort