Network Working Group A. Gwinn
Request for Comments: 2179 Networld+Interop NOC Team
Category: Informational July 1997
Network Security For Trade Shows
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
This document is designed to assist vendors and other participants in
trade shows, such as Networld+Interop, in designing effective
protection against network and system attacks by unauthorized
individuals. Generally, it has been observed that many system
administrators and trade show coordinators tend to overlook the
importance of system security at trade shows. In fact, systems at
trade shows are at least as prone to attack as office-based
platforms. Trade show systems should be treated as seriously as an
office computer. A breach of security of a trade show system can
render -- and has rendered -- an exhibitor's demonstrations
inoperable -- sometimes for the entire event!
This document is not intended to replace the multitudes of
comprehensive books on the subject of Internet security. Rather, its
purpose is to provide a checklist-style collection of frequently
overlooked, simple ways to minimize the chance of a costly attack.
We encourage exhibitors to pay special attention to this document and
share it with all associated representatives.
Physical Security
Before addressing technical security issues, one of the most
frequently underrated and overlooked security breaches is the simple
low-tech attack. The common victim is the one who leaves a console
logged in, perhaps as root, and leaves the system. Other times, an
anonymous "helpful soul" might ask for a password in order to assist
the user in "identifying a problem." This type of method allows an
intruder, especially one logged in as "root", access to system files.
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Tips:
* Educate sales and support staff regarding system logins, especially
"root" or other privileged accounts.
* Identify individuals who are not using exhibit systems for their
intended purpose, especially non-booth personnel.
* Request identification from anyone wishing to access systems
for maintenance purposes unless their identities are known.
System Security
This section discusses technical security procedures for workstations
on the vendor network. Although specifics tend to be for Unix
systems, general procedures apply to all platforms.
Password Security
Lack of passwords or easy to guess passwords are a relatively low-
tech door into systems, but are responsible for a significant number
of breakins. Good passwords are a cornerstone of system security.
By default, PC operating systems like Windows 95 and MacOS do not
provide adequate password security. The Windows login password
provides no security (hitting the "ESC" key allows the user to bypass
password entry). Password security for these machines is possible,
but is beyond the scope of this document.
Tips:
* Check /etc/passwd on Unix systems and the user administration
application on other systems for lack of passwords. Some vendors
ship systems with null passwords, in some cases even for
privileged accounts.
* Change passwords, especially system and root passwords.
* Mix case, numbers and punctuation, especially on privileged
accounts.
* Change system passwords on a regular basis.
* Do not use passwords relating to the event, the company, or
products being displayed. Systems personnel at Networld+Interop,
when asked to assist booth personnel, often guess even root
passwords!
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Extra Privileged Accounts
Some system vendors have been known to ship systems with multiple
privileged accounts (for example, Unix systems with accounts that
have root privileges [UID=0]). Some vendors may include a separate
system administration account that places a user in a specific
administrative program. Each additional privileged account presents
yet another opportunity for abuse.
Generally, if a Unix system does not need additional root accounts,
these can be disabled by placing "*" in the password field of
/etc/passwd, or by using the administrative tool when a system
employees enhanced security. Verify all systems for extra privileged
accounts and either disable them or change their password as
appropriate.
Make certain that privileged accounts are inaccessible from anywhere
other than the system console. Frequently systems rely on files such
as /etc/securettys for a list of "secure" terminals. As a general
rule, unless a terminal is in this file, a root login is not
possible. Specific use of this feature should be covered in the
system's documentation files.
Tips:
* Check /etc/passwd on Unix systems and the user administration
application on other systems for additional privileged accounts.
* Disable remote login for privileged accounts.
* Disable any unnecessary privileged accounts.
* Limit logins from root accounts to "secure" terminals or the
system console.
Use of Authentication Tokens
Authentication tokens such as SecureID, Cryptocard, DES Gold and
others, provide a method of producing "one-time" passwords. The
principle advantage in a trade-show environment is to render
worthless, packets captured by sniffers on the network. It should be
treated as fact, that there are many packet sniffers and other
administration tools constantly (legitimately) watching the network-
-especially at a large network-oriented trade show. Typed passwords,
by default, are sent clear text across the network, allowing others
to view them. Authentication tokens provide a password that is only
valid for that one instance, and are useless after that. A logical
extension of the use of authentication tokens would be to use them
for "trips home" (from the show network to a home site) to minimize
the chance of off-site security problems.
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An alternative to these tokens is the secure shell ("ssh") protocol
which provides an encrypted connection between clients and servers.
This connection can carry both login traffic and arbitrary port-to-
port communication, and is a powerful tool for securing an in-booth
network and communications to and from remote systems.
Tips:
* Contact vendors of authentication tokens/cards for further
information as to how to integrate into specific environments, or
on to specific platforms.
* The public-domain utility "cryptosu" (csu), when used with a
Cryptocard, provides a replacement for Unix's "su" command,
employing a challenge/response style of authentication for root
access.
* Explore the use of ssh clients and servers.
Anonymous FTP
Anonymous FTP accounts can easily turn into a security hole. Disable
this service if not specifically needed. In the event that anonymous
FTP is to be used, the following tips may help secure it.
* When a user logs in as "anonymous", they should be locked into a
specific directory tree. Be sure that FTPd properly chroots to the
appropriate directory. A "cd /" should put an anonymous user at the
top of the "public" tree, and not the system's root directory.
* Some systems may allow symbolic links (or "shortcuts") to take a
user outside the allowed tree. Verify all links inside the
anonymous FTP hierarchy.
* Make sure that ftp's root directory is "owned" by someone other
than the 'ftp' account. Typically, it should be owned by "root".
* Do not use a world-writable incoming directory unless absolutely
necessary. Many sites use these as a way for users to transfer
files into the site. This can, and frequently does, turn into an
archive for stolen software (referred to by the pirate community as
"warez").
* Removing read permissions from the directory permissions (chmod 733
on Unix systems) prohibits an anonymous user from being able to
list the contents of a directory. Files can be deposited as usual,
but not retrieved unless the user knows the exact name of the file.
Network File Sharing
Writable file shares without some form of security are invitations to
destruction of information and demonstrations. Whether using NFS on
Unix systems, or PC sharing facilities like CIFS, AppleShare, or
NetWare, close attention should be paid to security of the files
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exported. Keep in mind that one's competition frequently shares the
same network at a trade show! Security for both read and write
access should be employed and each access point examined.
Exporting a writable NFS filesystem to the world grants anyone the
ability to read and write any file in the exported mount point. If
this is done, for example, with a system directory such as "/" or
"/etc", it is a simple matter to edit password files to create one-
self access to a system. Therefore, /etc/exports should be closely
examined to be certain that nothing of a sensitive nature is exported
to anyone but another trusted host. Anything exported to the general
public should be exported "read-only", and verified for the
information that is available via the file shares.
Tips:
* Do not provide file sharing space unless needed.
* Verify where exported information will be "visible".
* Do not maintain any writable shares unless absolutely necessary!
Trusted Hosts
Trusted host entries are a method for allowing other hosts
"equivalent" security access to another host computer. Some vendors
ship systems with open trusted host files. Make certain that this
issue is addressed.
Tips:
* On Unix systems, check for a '+' entry (all systems trusted) in
/etc/hosts.equiv and all ".rhosts" files (there may be multiple
.rhosts files) and remove it.
* Check for an "xhost +" entry in the "...X11/xdm/Xsession" file.
Most often, an "xhost" entry will appear with a pathname such as
"/usr/local/lib/xhost +". Remove this.
SetUID and SetGID binaries (Unix systems)
On Unix systems, the "suid" bit on a system executable program allows
the program to execute as the owner. A program that is setUID to
"root" will allow the program to execute with root privileges. There
are multiple legitimate reasons for a program to have root
privileges, and many do. However, it may be unusual to have suid
programs in individual user directories or other non-system places. A
scan of the filesystems can turn up any program with its suid or sgid
bit set. Before disabling any programs, check the legitimacy of the
files.
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Tips:
* "find / -user root -perm -4000 -print" will find any occurrence of
a setuid file anywhere in the system, including those on NFS
mounted partitions.
* "find / -group kmem -perm -2000 -print" will do the same for kmem
group permissions.
System Directory Ownership and Write Permissions
Check ownership of all system directories and permissions needed to
write or modify files. There is no simple way to do this on PC
operating systems like Windows NT without simply checking all files
and directories or using a version of "ls" that will list ACLs.
On Unix systems, a directory with permissions such as "drwxrwxrwx"
(such as /tmp) is world-writable and anyone can create or modify
files in such area. Pay special attention to "/" and "/etc". These
should be owned by some system account-not by an individual user.
When in doubt, contact the vendor of the system software for
confirmation of the appropriate directory or file permissions.
Network Services
Any servers not needed should be disabled. The notorious "R services"
(rexec, rsh, and rlogin) are particularly prone to security problems
and should be disabled unless specifically needed. Pay particular
attention to trusted hosts files, and be aware of the risk of IP
spoofing attacks from machines "pretending" to be trusted hosts.
Tips:
* On Unix systems, comment out "R services" (rexec, rsh, rlogin) in
/etc/inetd.conf.
* Check for other unknown or unneeded services.
Trivial File Transfer Protocol (TFTP)
TFTP can be an easy way for an intruder to access system files. It is
good general practice to disable TFTP. If TFTP is needed, verify
that only files targeted for export are accessible. A simple way to
check security is to attempt to tftp files such as /etc/passwd or
/etc/motd to check accessiblity of system files.
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TCP Connection Monitoring
Public domain software (TCP Wrappers or "tcpd" for Unix systems)
allow restriction and monitoring of TCP connections on a host by host
basis. Systems can be configured to notify an administrator and
syslog when any unauthorized party attempts to access the host. This
software is available from:
* ftp://info.cert.org/pub/tools/tcp_wrappers/
BIND (Berkeley Internet Name Daemon)
Earlier versions of BIND have been prone to various attacks. If a
host is going to be acting as DNS, use the latest version of BIND.
It is available at:
* ftp://ftp.isc.org/isc/bind
Sendmail and Mailer Security
A great number of previous versions of Sendmail have known security
holes. Check installed sendmail for the most recent version.
Alternatively, consult the operating system vendor to get the most
recent release for the platform.
Web Server Scripting Security
All Web server scripts and binaries should be checked (especially the
"...httpd/cgi-bin" directory) for those that allow shell commands to
be executed. Many attacks in recent months have focused on the use of
utilities such as "phf" for accessing /etc/passwd on a target system.
Remove any script that is not needed in the course of operation of a
web server.
Other Suggestions
* Check with the vendor of the operating system for known security
issues. Make certain that all systems have the latest version of
software--especially security patches to fix specific problems.
* Examine log files on the host frequently. On Unix systems, the
"last" command will furnish information on recent logins and where
they came from. The "syslogs" or "Event Viewer" will contain more
specific information on system events.
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* Web server logfiles (...httpd/log/access_log and
...httpd/log/error_log) will contain information on who has been
accessing a WWW server, what has been accessed, and what has
failed.
* Good backups are the best defense against system damage. Perform
backups before placing a system on the trade show network then
continue backups throughout the show and again following the event.
A final backup set is useful to examine for possible attempts at
(or successful) penetrations of system security.
General Network Security
As would be expected at network trade shows (large or otherwise),
there are many entities running packet sniffers. Most are exhibitors
who have a legitimate need to run them during the course of product
demonstrations. However, be aware that there are many "listening
ears" on network segments--any of whom can "hear" or "see"
information as it crosses the net. Particularly prone to
eavesdropping are telnet sessions. A good rule of thumb is to assume
that "when you type your password, the only one that doesn't see it
is you!"
It is a good practice to not log in (or "su") to an account with
privileges across the network if at all possible. As mentioned
previously, authentication tokens and ssh are a simple way to add
security to system account access.
Packet Filtering
Many routers support basic packet filtering. If a router can be
deployed between the local network and the show's network, general
basic packet filtering should be employed. Below is a good "general"
packet filter approach. The approach itself is ordered into
categories:
* General global denials/acceptance.
* Specific global service denials.
* Specific service acceptance.
* Final denial of all other TCP/UDP services.
Based on the theory of denying everything that you don't know is
acceptable traffic, a good approach to a filter ruleset, in order of
execution priority, might be:
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General Global Denials/Acceptance
1 Filter spoofed source addresses by interface. Match source
addresses to routing information available for the interface.
Discard packets with source addresses arriving on one interface
(from the "outside" for example) claiming a source address on
another interface (the "inside").
2 Filter all source routed packets unless source routing is
specifically needed.
3 Allow outbound connections from "inside" hosts.
4 Allow established TCP connections (protocol field contains 6 and
the TCP flags field either contains ACK or does NOT contain SYN
bit). Only filter requests for 'new' connections.
5 Filter 'new' connections with source port of 25. Prevents people
from pretending to be a remote mail server.
6 Filter loopback address (source address 127.0.0.1). Prevents
packets from a misconfigured DNS resolver.
Specific Global Service Denials
1 Specifically block all "R-command" ports
(destination ports 512-515).
2 Block telnet (destination port 23) from any host not requiring
telnet access from the outside. (If you use ssh, you can
block it from all hosts!)
3 Add specific filters to deny other specific protocols to the
network, as needed.
Specific Host/Service Acceptance
1 Add specific access to specific "public" hosts' services
(unsecure FTP or WWW servers).
2 Allow SMTP (source and destination port 25) for electronic mail
to the mail server(s).
3 Allow inbound FTP connections (source port 20) to the FTP server(s).
4 Allow DNS (source and destination port 53, UDP & TCP) to name servers.
If zone transfers are not needed, block the TCP ports.
5 Allow RIP packets in (source and destination port 520, UDP), if
appropriate.
6 Add specific filters to allow other desired specific protocols
or to open certain ports to specific machines.
Final Service Denial
1 Deny all other UDP and TCP services not allowed by the previous
filters.
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Author's Address
R. Allen Gwinn, Jr.
Associate Director, Computing
Business Information Center
Southern Methodist University
Dallas, TX 75275
Phone: 214/768-3186
EMail: allen@mail.cox.smu.edu or allen@radio.net
Contributing Writer
Stephen S. Hultquist
President
Worldwide Solutions, Inc.
4450 Arapahoe Ave., Suite 100
Boulder, CO 80303
Phone: +1.303.581.0800
EMail: ssh@wwsi.com
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