Unix security FAQ

Unix security FAQ


Archive-name: security-faq Last-modified: 1993/12/3 Version: 2.2

Version History:
2.2 LD_LIBRARY_PRELOAD comment 2.1 New story, TAMU package info 2.0 MERGE IN LOTS OF NEW INFORMATION 1.6 Minor revisions, meant to bring it a bit more up to date. 1.5 Structural revision. 1.4 Fixed John Haugh's name, modified entry for "shadow"
      Added Ulf Kieber's update on the rainbow series
      Added bit about Karila paper 1.3: Tweak for comp.security.misc/news.answers
      Updated entry for orange book (foreign purchases) 1.2: Undocumented prior to this


      Almost Everything You Ever Wanted To Know About Security*
      *(but were afraid to ask!)
This document is meant to answer some of the questions which regularly appear in the Usenet newsgroups "comp.security.misc", "comp.security.unix", and "alt.security", and is meant to provide some background to the subject for newcomers to that newsgroup.


This FAQ is maintained by Alec Muffett (Alec.Muffett@UK.Sun.COM), with contributions from numerous others; the views expressed in the document are the personal views of the author(s), and it should not be inferred that they are necessarily shared by anyone with whom the author(s) are now, or ever may be, associated.
Many thanks go to (in no particular order): Steve Bellovin, Matt Bishop, Mark Brader, Ed DeHart, Dave Hayes, Jeffrey Hutzelman, William LeFebvre, Wes Morgan, Rob Quinn, Chip Rosenthal, Wietse Venema, Gene Spafford, John Wack and Randall Atkinson.
Disclaimer: Every attempt is made to ensure that the information contained in this FAQ is up to date and accurate, but no responsibility will be accepted for actions resulting from information gained herein.
Questions which this document addresses:
Q.1 What are alt.security and comp.security.misc for? Q.2 Whats the difference between a hacker and a cracker? Q.3 What is "security through obscurity" Q.4 What makes a system insecure? Q.5 What tools are there to aid security? Q.6 Where can I get these tools? Q.7 Isn't it dangerous to give cracking tools to everyone? Q.8 Why and how do systems get broken into? Q.9 Who can I contact if I get broken into? Q.10 What is a firewall? Q.11 Why shouldn't I use setuid shell scripts? Q.12 Why shouldn't I leave "root" permanently logged on the console? Q.13 Why shouldn't I create Unix accounts with null passwords? Q.14 What security holes are associated with X-windows (and other WMs)? Q.15 What security holes are associated with NFS? Q.16 How can I generate safe passwords? Q.17 Why are passwords so important? Q.18 How many possible passwords are there? Q.19 Where can I get more information? Q.20 How silly can people get?

Q.1 What are alt.security and comp.security.misc for?
Comp.security.misc is a forum for the discussion of computer security, especially those relating to Unix (and Unix like) operating systems. Alt.security used to be the main newsgroup covering this topic, as well as other issues such as car locks and alarm systems, but with the creation of comp.security.misc, this may change.
This FAQ will concentrate wholly upon computer related security issues.
The discussions posted range from the likes of "What's such-and-such system like?" and "What is the best software I can use to do so-and-so" to "How shall we fix this particular bug?", although there is often a low signal to noise ratio in the newsgroup (a problem which this FAQ hopes to address).
The most common flamewars start when an apparent security novice posts a message saying "Can someone explain how the such-and-such security hole works?" and s/he is immediately leapt upon by a group of self appointed people who crucify the person for asking such an "unsound" question in a public place, and flame him/her for "obviously" being a cr/hacker.
Please remember that grilling someone over a high flame on the grounds that they are "a possible cr/hacker" does nothing more than generate a lot of bad feeling. If computer security issues are to be dealt with in an effective manner, the campaigns must be brought (to a large extent) into the open.
Implementing computer security can turn ordinary people into rampaging paranoiacs, unable to act reasonably when faced with a new situation. Such people take an adversarial attitude to the rest of the human race, and if someone like this is in charge of a system, users will rapidly find their machine becoming more restrictive and less friendly (fun?) to use.
This can lead to embarrasing situations, eg: (in one university) banning a head of department from the college mainframe for using a network utility that he wasn't expected to. This apparently required a lot of explaining to an unsympathetic committee to get sorted out.
A more sensible approach is to secure a system according to its needs, and if its needs are great enough, isolate it completely. Please, don't lose your sanity to the cause of computer security; it's not worth it.

      usenet/comp.sources.misc/volume29
      usenet/comp.sources.misc/volume30
      usenet/comp.sources.misc/volume32

Q.2 What's the difference between a hacker and a cracker?
Lets get this question out of the way right now:
On USENET, calling someone a "cracker" is an unambiguous statement that some person persistently gets his/her kicks from breaking from into other peoples computer systems, for a variety of reasons. S/He may pose some weak justification for doing this, usually along the lines of "because it's possible", but most probably does it for the "buzz" of doing something which is illicit/illegal, and to gain status amongst a peer group.
Particularly antisocial crackers have a vandalistic streak, and delete filestores, crash machines, and trash running processes in pursuit of their "kicks".
The term is also widely used to describe a person who breaks copy protection software in microcomputer applications software in order to keep or distribute free copies.
On USENET, calling someone a "hacker" is usually a statement that said person holds a great deal of knowledge and expertise in the field of computing, and is someone who is capable of exercising this expertise with great finesse. For a more detailed definition, readers are referred to the Jargon File [Raymond].
In the "real world", various media people have taken the word "hacker" and coerced it into meaning the same as "cracker" - this usage occasionally appears on USENET, with disastrous and confusing results.
Posters to the security newsgroups should note that they currently risk a great deal of flamage if they use the word "hacker" in place of "cracker" in their articles.
NB: nowhere in the above do I say that crackers cannot be true hackers. It's just that I don't say that they are...

Q.3 What is "security through obscurity"
Security Through Obscurity (STO) is the belief that any system can be secure so long as nobody outside of its implementation group is allowed to find out anything about its internal mechanisms. Hiding account passwords in binary files or scripts with the presumption that "nobody will ever find it" is a prime case of STO.
STO is a philosophy favoured by many bureaucratic agencies, and it used to be a major method of providing "pseudosecurity" in computing systems.
Its usefulness has declined in the computing world with the rise of open systems, networking, greater understanding of programming techniques, as well as the increase in computing power available to the average person.
The basis of STO has always been to run your system on a "need to know" basis. If a person doesn't know how to do something which could impact system security, then s/he isn't dangerous.
Admittedly, this is sound in theory, but it can tie you into trusting a small group of people for as long as they live. If your employees get an offer of better pay from somewhere else, the knowledge goes with them, whether the knowledge is replaceable or not. Once the secret gets out, that is the end of your security.
Nowadays there is also a greater need for the ordinary user to know details of how your system works than ever before, and STO falls down a as a result. Many users today have advanced knowledge of how their operating system works, and because of their experience will be able to guess at the bits of knowledge that they didn't "need to know". This bypasses the whole basis of STO, and makes your security useless.
Hence there is now a need is to to create systems which attempt to be algorithmically secure (Kerberos, Secure RPC), rather than just philosophically secure. So long as your starting criteria can be met, your system is LOGICALLY secure.
Incidentally, "Shadow Passwords" (below) are sometimes dismissed as STO, but this is incorrect, since (strictly) STO depends on restricting access to an algorithm or technique, whereas shadow passwords provide security by restricting access to vital data.

Q.4 What makes a system insecure?
Switching it on. The adage usually quoted runs along these lines:

      "The only system which is truly secure is one which is switched off
      and unplugged, locked in a titanium lined safe, buried in a concrete
      bunker, and is surrounded by nerve gas and very highly paid armed
      guards. Even then, I wouldn't stake my life on it."
(the original version of this is attributed to Gene Spafford)
A system is only as secure as the people who can get at it. It can be "totally" secure without any protection at all, so long as its continued good operation is important to everyone who can get at it, assuming all those people are responsible, and regular backups are made in case of hardware problems. Many laboratory PC's quite merrily tick away the hours like this.
The problems arise when a need (such as confidentiality) has to be fulfilled. Once you start putting the locks on a system, it is fairly likely that you will never stop.
Security holes manifest themselves in (broadly) four ways:
1) Physical Security Holes.
- Where the potential problem is caused by giving unauthorised persons physical access to the machine, where this might allow them to perform things that they shouldn't be able to do.
A good example of this would be a public workstation room where it would be trivial for a user to reboot a machine into single-user mode and muck around with the workstation filestore, if precautions are not taken.
Another example of this is the need to restrict access to confidential backup tapes, which may (otherwise) be read by any user with access to the tapes and a tape drive, whether they are meant to have permission or not.
2) Software Security Holes
- Where the problem is caused by badly written items of "privledged" software (daemons, cronjobs) which can be compromised into doing things which they shouldn't oughta.
The most famous example of this is the "sendmail debug" hole (see bibliography) which would enable a cracker to bootstrap a "root" shell. This could be used to delete your filestore, create a new account, copy your password file, anything.
(Contrary to popular opinion, crack attacks via sendmail were not just restricted to the infamous "Internet Worm" - any cracker could do this by using "telnet" to port 25 on the target machine. The story behind a similar hole (this time in the EMACS "move-mail" software) is described in [Stoll].)
New holes like this appear all the time, and your best hopes are to:

      a: try to structure your system so that as little software as possible
      runs with root/daemon/bin privileges, and that which does is known to
      be robust.

      b: subscribe to a mailing list which can get details of problems
      and/or fixes out to you as quickly as possible, and then ACT when you
      receive information.
>From: Wes Morgan > > c: When installing/upgrading a given system, try to install/enable only > those software packages for which you have an immediate or foreseeable > need. Many packages include daemons or utilities which can reveal > information to outsiders. For instance, AT&T System V Unix' accounting > package includes acctcom(1), which will (by default) allow any user to > review the daily accounting data for any other user. Many TCP/IP packa- > ges automatically install/run programs such as rwhod, fingerd, and > tftpd, all of which can present security problems. > > Careful system administration is the solution. Most of these programs > are initialized/started at boot time; you may wish to modify your boot > scripts (usually in the /etc, /etc/rc, /etc/rcX.d directories) to pre- > vent their execution. You may wish to remove some utilities completely. > For some utilities, a simple chmod(1) can prevent access from unauthorized > users. > > In summary, DON'T TRUST INSTALLATION SCRIPTS/PROGRAMS! Such facilities > tend to install/run everything in the package without asking you. Most > installation documentation includes lists of "the programs included in > this package"; be sure to review it.
3) Incompatible Usage Security Holes
- Where, through lack of experience, or no fault of his/her own, the System Manager assembles a combination of hardware and software which when used as a system is seriously flawed from a security point of view. It is the incompatibility of trying to do two unconnected but useful things which creates the security hole.
Problems like this are a pain to find once a system is set up and running, so it is better to build your system with them in mind. It's never too late to have a rethink, though.
Some examples are detailed below; let's not go into them here, it would only spoil the surprise.
4) Choosing a suitable security philosophy and maintaining it.
>From: Gene Spafford >The fourth kind of security problem is one of perception and >understanding. Perfect software, protected hardware, and compatible >components don't work unless you have selected an appropriate security >policy and turned on the parts of your system that enforce it. Having >the best password mechanism in the world is worthless if your users >think that their login name backwards is a good password! Security is >relative to a policy (or set of policies) and the operation of a system >in conformance with that policy.

Q.5 What tools are there to aid security Q.6 ...and... where can I get these tools?
================================================================== *** This is a section which has changed very rapidly over the past *** few months; hence I am changing the format ever so slightly, in *** order to allow for expansion - Alec ==================================================================
COPS Dan Farmer, et al.
Managed/largely written by Dan Farmer, COPS is a suite of shell scripts which forms an extensive security testing system; there's a rudimentary password cracker, and routines to check the filestore for suspicious changes in setuid programs, others to check permissions of essential system and user files, and still more to see whether any system software behaves in a way which could cause problems.
The software comes in two versions - one written in Perl and one (largely equivalent) written in shell scripts. The latest version is very up-to-date on Unix Security holes.
COPS V1.04 is available for FTP from cert.org in pub/cops and archive.cis.ohio-state.edu in pub/cops.
Crack Alec Muffett UFC Michael Glad
Crack is a program written with one purpose in mind: to break insecure passwords. It is probably the most efficent and friendly password cracker that is publically available, with the ability to let the user to specify precisely how to form the words to use as guesses at users passwords.
It also has an inbuilt networking capability, allowing the load of cracking to be spread over as many machines as are available on a network, and it is supplied with an optimised version of the Unix crypt() algorithm.
An even faster version of the crypt() algorithm, "UFC" by Michael Glad, is freely available on the network, and the latest versions of UFC and Crack are compatible and can be easily hooked together.
Crack v4.1f and UFC are available from: ftp.uu.net (137.39.1.9)
In the directory: /usenet/comp.sources.misc/volume28 As: crack/part01.Z to part05.Z ( 5 files ) And ufc-crypt/part01.Z & part02.Z ( 2 files )
NB: For people with access to a Connection Machine:
>From: glad@daimi.aau.dk (Michael Glad) > >A UNIX password cracker for the Thinking Machine CM/2 and CM/200 >Connection Machines is available for FTP from > > ftp.denet.dk:/pub/misc/cm200-UFC.tar.Z > > This is a password cracker for the Thinking Machines CM/2 and CM/200 > Connection Machines. It features > > o A standalone dictionary preprocessor accepting a > language of rewrite rules compatible with the one > found in Alec Muffets 'Crack' password cracker as of > release 4.1f. > > o An optimized port of the UFC-crypt: a fast implementation > of the UNIX crypt(3) function developed by Michael Glad and > donated to the Free Software Foundation (FSF). > > o The password cracker itself. It supports restart of crashed > runs and incremental use. Incremental use means that when > you use a fixed dictionary, the cracker can maintain a status > file of already cracked passwords and passwords considered > uncrackable (because they've been tested in previous runs). > Thus it only has to waste CPU cycles on new accounts and accounts > with changed passwords. > > o When run with a _large_ dictionary (a 1 million word dictionary > obtained by preprocessing /usr/dict/words), the cracker can > test in excess of 50,000 passwords a second on a CM/200 with > 8192 processors.
CrackLib Alec Muffett
Cracklib is a C LIBRARY containing a routine which may be wired into all sorts of "passwd"-like programs; not just Unix, but with a little effort it could probably go onto VMS (this is being worked upon), or many other systems.
Using "CrackLib" allows you to wire proactive password checking into _any_ of your applications; it is an offshoot of the the version 5 "Crack" software, and contains a considerable number of ideas nicked from the new software.
CrackLib was posted to "comp.sources.misc", and therefore available from any major usenet archive. A reference copy (+ large dictionary) can be FTP'ed from:

      black.ox.ac.uk:~ftp/src/security/cracklib25.tar.Z
NB: if you search for CrackLib on "Archie", care should be taken to get the package from a comp.sources.misc archive; beware confusing it with a package of the same name, which was hacked into "npasswd".
NPasswd Clyde Hoover Passwd+ Matt Bishop Shadow John F. Haugh II
Passwd+ & NPasswd: these programs are written to redress the balance in the password cracking war. They provide replacements for the standard "passwd" command, but prevent a user from selecting passwords which are easily compromised by programs like Crack.
The usual term for this type of program is a 'fascist' password program.
NPasswd: Currently suffering from being hacked about by many different people, in order to provide compatibility for System V based systems, NIS/YP, shadow password schemes, etc. Version 2.0 is in the offing, but many versions exist in many different configurations.
Passwd+: "alpha version, update 3" - beta version due soon. Available from dartmouth.edu as pub/passwd+.tar.Z
Shadow: is a set of program and function replacements (compatible with most Unixes) which implements shadow passwords, ie: a system where the plaintext of the password file is hidden from all users except root, hopefully stopping all password cracking attempts at source. In combination with a fascist passwd frontend, it should provide a good degree of password file robustness.
>From: jfh@rpp386.cactus.org (John F. Haugh II) >Shadow does much more than hide passwords. It also provides for >terminal access control, user and group administration, and a few >other things which I've forgotten. There are a dozen or more >commands in the suite, plus a whole slew of library functions.
Shadow is available from the comp.sources.misc directory at any major USENET archive - relevant files are in:

      usenet/comp.sources.misc/volume38
      usenet/comp.sources.misc/volume39
- the contents of both of which are needed, for a full set of patches.
Given that the latest release of Shadow has a hook for "CrackLib" support, it now ranks as a full blown fascist password program, on top of its other functionality.
CrackLib support is expected in Passwd+, in the near future.
TCP Wrappers Wietse Venema
These are programs which provide front-end filters to MOST of the network services which Unix provides by default.
If installed, they can curb otherwise unrestricted access to potential dangers like incoming FTP/TFTP, Telnet, etc, and can provide extra logging information, which may be of use if it appears that someone is trying to break in.
>From the BLURB
>With these programs you can monitor and control who connects to your >TFTP, EXEC, FTP, RSH, TELNET, RLOGIN, FINGER, and SYSTAT network >services, and many others. > >The programs can be installed without any changes to existing software >or configuration files. By default, they just log the remote host name >and do some sanity checks on the origin of the request. No information >is exchanged with the remote client process. > >Significant differences with respect to the previous release: > > - Easier to install: ready-to-use build procedures for many common > UNIX implementations (sun, ultrix, hp-ux, irix, aix, ...). > > - Support for the System V.4 TLI network programming interface > (Solaris, DG/UX etc.). In case of TLI applications on top of > TCP/IP, the wrappers provide the same functionality as with > socket-based applications. > > - A more secure finger tool for automatic reverse finger probes. > > - New extension language keywords: "severity", to adjust the log > noise level; "allow" and "deny", to keep all access-control rules > within a single file. > > - More support for selective remote username lookups. > > - More workarounds for System V bugs: IRIX username lookups, and > SCO problems with UDP. > > The default mode of operation (no TLI support) should be backwards > compatible with earlier versions. The library interface has changed, > though, and programs that depend on the libwrap.a library will have to > be recompiled before they can be relinked. > > Wietse Venema (wietse@wzv.win.tue.nl)
TCP Wrappers are available for anonymous FTP from:

      cert.org:pub/tools/tcp_wrappers
SecureLib William LeFebvre
>From: phil@pex.eecs.nwu.edu >You may want to add a mention of securelib, a security enhancer >available for SunOS version 4.1 and higher.
>Securelib contains replacement routines for three kernel calls: >accept(), recvfrom(), recvmsg(). These replacements are compatible with >the originals, with the additional functionality that they check the >Internet address of the machine initiating the connection to make sure >that it is "allowed" to connect. A configuration file defines what >hosts are allowed for a given program. Once these replacement routines >are compiled, they can be used when building a new shared libc library. >The resulting libc.so can then be put in a special place. Any program >that should be protected can then be started with an alternate >LD_LIBRARY_PATH.
The latest version of securelib is available via anonymous FTP from the host "eecs.nwu.edu". It is stored in the file "pub/securelib.tar".
ISS Chris Klaus YPX Rob Nauta
>Internet Security Scanner (ISS) is one of the first multi-level security >scanners available to the public. It was designed to be flexible and >easily portable to many unix platforms and do its job in a reasonable >amount of time. It provides information to the administrator that will >fix obvious security misconfigurations. > >ISS does a multi-level scan of security, not just searching for one >weakness in the system. To provide this to the public or at least to >the security conscious crowd may cause people to think that it is too >dangerous for the public, but many of the (cr/h)ackers are already aware >of these security holes and know how to exploit them. > >These security holes are not deep in some OS routines, but standard >misconfigurations that many domains on Internet tend to show. Many of >these holes are warned about in CERT and CIAC advisories. This is the >first release of ISS and there is still much room for improvement.
[...A simplistic description of ISS might be that it is to the Unix Network Services, what COPS is to the Unix filesystem; ie: a tool to allow a systems administrator to find potential holes, giving him/her a chance to solve the problem BEFORE a cracker attack an occur.
ISS and an auxilliary program, YPX, have been recently posted to comp.sources.misc. Because ISS is in a early stage of development, check an "Archie" site for the most up-to-date information...Alec]
TripWire Gene Kim, Gene Spafford
[From the Announce file]
>Tripwire is an integrity-monitor for Unix systems. It uses several >checksum/signature routines to detect changes to files, as well as >monitoring selected items of system-maintained information. The system >also monitors for changes in permissions, links, and sizes of files and >directories. It can be made to detect additions or deletions of files >from watched directories. > >The configuration of Tripwire is such that the system/security >administrator can easily specify files and directories to be monitored >or to be excluded from monitoring, and to specify files which are >allowed limited changes without generating a warning. Tripwire can also >be configured with customized signature routines for site-specific >checks. > >Tripwire, once installed on a clean system, can detect changes from >intruder activity, unauthorized modification of files to introduce >backdoor or logic-bomb code, (if any were to exist) virus activity in >the Unix environment. > >Tripwire is provided as source code with documentation. The system, as >delivered, performs no changes to system files and does not require root >privilege to run (in the general case). The code has been beta-tested >in a form close to that of this release at over 100 sites world-wide. >Tripwire should work on almost any version of Unix, from Xenix on >80386-based machines to Cray and ETA-10 supercomputers. > >Tripwire may be used without charge, but it may not be sold or modified >for sale. Tripwire was written as a project under the auspices of the >COAST Project at Purdue University. The primary author was Gene Kim, >with the aid and under the direction of Gene Spafford (COAST director). > >Copies of the Tripwire distribution may be ftp'd from ftp.cs.purdue.edu >from the directory pub/spaf/COAST/Tripwire. The distribution is >available as a compressed tar file, and as uncompressed shar kits. The >shar kit form of Tripwire version 1.0 will also be posted to >comp.sources.unix on the Usenet. > >A mailserver exists for distribution and to support a Tripwire mailing >list. To use the mail server, send e-mail to >"tripwire-request@cs.purdue.edu" with a message body consisting solely >of the word "help". The server will respond with instructions on how to >get source, patches, and how to join the mailing list. > >Questions, comments, complaints, bugfixes, etc may be directed to: >genek@mentor.cc.purdue.edu (Gene Kim) >spaf@cs.purdue.edu (Gene Spafford)
TAMU Dave Safford, Doug Schales, Dave Hess
>From the ANNOUNCE file:
> Texas A&M Network Security Package Update > 7/1/93 > > Dave Safford > Doug Schales > Dave Hess > >This is an updated release of the security tools developed at the >Texas A&M University Supercomputer Center. These tools are available >for anonymous FTP from net.tamu.edu:/pub/security/TAMU. [...] >ORIGINAL DESCRIPTION: > >Last August, Texas A&M University UNIX computers came under extensive >attack from a coordinated group of internet crackers. This package of >security tools represents the results of over nine months of >development and testing of the software we have been using to protect >our estimated five thousand IP devices. This package includes three >coordinated sets of tools: "drawbridge", an exceptionally powerful >bridging filter package; "tiger", a set of convenient yet thorough >machine checking programs; and "netlog", a set of intrusion detection >network monitoring programs. > >KEY FEATURES: > >For full technical details on the products, see their individual README's, >but here are some highlights: > > DRAWBRIDGE: > - inexpensive (PC with two SMC/WD 8013 cards) > - high level filter language and compiler > - powerful filtering parameters > - DES authenticated remote filter management > - O(1) table lookup processing even with dense class B > net filter specifications. > > TIGER: > - checks key binaries against cryptographic > checksums from original distribution files > - checks for critical security patches > - checks for known intrusion signatures > - checks all critical configuration files > - will run on most UNIX systems, and has tailored > components for SunOS, Next, SVR4, Unicos. > > NETLOG: > - efficiently logs all tcp/udp establishment attempts > - powerful query tool for analyzing connection logs > - "intelligent" intrusion detection program > >AVAILABILITY: > >This package is available via anonymous ftp in > > net.tamu.edu: pub/security/TAMU > >Due to the sensitive nature of these tools, we recommend that you >retrieve them from this location. If you do not get them from >net.tamu.edu we suggest that you use our check_TAMU script that uses >cryptographic checksums to check the distribution for any signs of >tampering. The script is available in the anonymous ftp directory above >and from an e-mail server at: > > drawbridge-server@net.tamu.edu > >Note that there are some distribution limitations, such as the >inability to export outside the US the DES libraries used in >drawbridge; see the respective tool README's for details of any >restrictions. (Note that the DES libraries are NOT required to use >drawbridge. They just enable secure remote management of drawbridge.) > >CONTACT: > >Comments and questions are most welcome. Please address them to: > > drawbridge@net.tamu.edu
[A wonderful paper about TAMU was presented at the 4th USENIX Security Symposium, and is reprinted in the proceedings of the same - Alec]
SPI
>From: Gene Spafford >Sites connected with the Department of Energy and some military >organizations may also have access to the SPI package. Interested (and >qualified) users should contact the CIAC at LLNL for details.
>SPI is a screen-based administrator's tool that checks configuration >options, includes a file-change (integrity) checker to monitor for >backdoors and viruses, and various other security checks. Future >versions will probably integrate COPS into the package. It is not >available to the general public, but it is available to US Dept of >Energy contractors and sites and to some US military sites. A version >does or will exist for VMS, too. Further information on availabilty can >be had from the folks at the DoE CIAC.
[...A paper on SPI was recently presented at the 1993 USENIX Security symposium; apparently v2.1 has appeared on an anonymous FTP site recently, but whether this is in accordance with licencing agreements is unknown to the author of this FAQ, and anyway, he's forgotten what the IP address was, so...]
TIS Firewall Toolkit Trusted Information Systems, Inc.
>From: mjr@tis.com (Marcus J. Ranum) > >Version 1.0 of the TIS network firewall toolkit is now available for >anonymous FTP from ftp.tis.com, in directory pub/firewalls/toolkit > >WHAT IS THE TIS FIREWALL TOOLKIT? >--------------------------------- >Trusted Information Systems, Inc. (TIS) is pleased to provide the TIS >Firewall Toolkit, a software kit for building and maintaining >internetwork Firewalls. It is distributed in source code form, with all >modules written in the C programming language and runs on many BSD UNIX >derived platforms. The Toolkit is being made available for use as >specified in the license agreement (LICENSE). > >The firewall toolkit is a set of programs, configuration practices, and >documentation intended to help individuals who are trying to build >internet firewalls. Included with the kit are complete sources for FTP, >rlogin, and telnet application proxies, user authentication management, >compartmented SMTP, and logging/log reduction. > >USERS' GROUP >------------ >TIS maintains the electronic-mail users' group for >discussion of the toolkit. To join, send electronic mail to >. > >TIS Firewall Toolkit technical questions, license issues, bug reports, >etc. should be addressed to . > >Information about other TIS network security products or commercial >licensing requests should be sent to or by telephone to >(301) 854-6889. > > >The contents of pub/firewalls/toolkit are as follows: >README - This file >fwtk-doc-only.tar.Z - Toolkit documentation >fwtk.tar.Z - Toolkit sources and Makefiles (no documentation) >US-only - Directory containing US-only software. If you > are not accessing this from a site in the US or > canada you will not be able to FTP these files. > The toolkit is still useable without these files.
SOCKS Ying-Da Lee/David Koblas
>From: ylee@syl.dl.nec.com (Ying-Da Lee) > >(This is a package that allows hosts behind a firewall the use of >finger, ftp, telnet, xgopher, and xmosaic to access the resources >outside of the firewall while maintaining the security requirements.) > >A new release of SOCKS is available for anonymous ftp from > > host ftp.inoc.dl.nec.com (143.101.112.3), > file pub/security/socks.cstc.4.0.tar.gz > >This version is intended to run with identd user verification (RFC 1413), >which is available as file pub/security/pidentd-2.1.2.tar.gz. > >Both of these are in Gnu's compressed form and required gzip to >uncompress them. If you don't already have that you can also pick up >the file pub/gnu/gzip-1.1.2.tar.Z. Remember to download them in binary >mode. > > >I am enclosing the first part of the README.1st file which describes the >new fearures. Besides SunOS 4.1.x, the new version has also been ported >and tested on ULTRIX 4.3, IRIX 4.0.1, and partially on HPUX, thanks to >Ian Dunkin and Anthony Shipman. > >Hope you can make good use of the package. Enjoy it. > >**** >This is SOCKS, a package consisting of a proxy server (sockd) and client >programs corresponding to finger, whois, ftp, telnet, xgopher, and >xmosaic, as well as a library module (libsocks.a) for adapting other >applications into new client programs. > >The original SOCKS was written by David Koblas , >which included the library module and finger, whois, and ftp clients. > >Clients programs added since the original are: > >-telnet: adapted from telnet.91.03.25 by David Borman . > This version is supposed to be much easier than the previous one > to port to many different systems. >-xgopher: adapted from xgopher ver. 1.2 by Allan Tuchman . >-xmosaic: adapted from xmosaic ver. 1.2 by NCSA staff (contact > Marc Andreesen, ). > >The SOCKS protocol has changed with this version. Since the server and >the clients must use the same SOCKS protocol, this server does not work >with clients of previous releases, and these clients do not work with >servers of previous releases. > >The access control mechanism has been expanded: > >-A list of users can be included along with other fields (source address, > destination address, service/port) for permission/denial of access. >-Identd is used (controlled by option -i and -I) in SOCKS server to try > to verify the actual user-ids. The code uses the library written by > Peter Eriksson and /Pdr Emanuelsson . >-A shell command can optionally be specified with each line. The command > is executed if the conditions of that line are satisfied. This is adapted > from the same feature and code used in the log_tcp package by Wietse > Venema . >-Special entries (#NO_IDENTD: and #BAD_ID:) can be included to specify > shell commands to be executed when the client host doesn't run identd > and when identd's report doesn't agree with what the client prgram says. > >[...] >The package has been ported for ULTRIX 4.3 by Ian Dunkin and Anthony >Shipman, for IRIX 4.0.1 by Ian Dunkin (again), and partially for HPUX by >Anthony Shipman (again!). (We are a small bunch of busy bees) I also >include patches by Craig Metz to SOCKSize xarchie and ncftp. I have not >try these patches out myself though. >[...]
==================================================================
Q.7 Isn't it dangerous to give cracking tools to everyone?
That depends on your point of view. Some people have complained that giving unrestricted public access to programs like COPS and Crack is irresponsible because the "baddies" can get at them easily.
Alternatively, you may believe that the really bad "baddies" have had programs like this for years, and that it's really a stupendously good idea to give these programs to the good guys too, so that they may check the integrity of their system before the baddies get to them.
So, who wins more from having these programs freely available? The good guys or the bad ? You decide, but remember that less honest tools than COPS and Crack tools were already out there, and most of the good guys didn't have anything to help.

Q.8 Why and how do systems get broken into?
This is hard to answer definitively. Many systems which crackers break into are only used as a means of entry into yet more systems; by hopping between many machines before breaking into a new one, the cracker hopes to confuse any possible pursuers and put them off the scent. There is an advantage to be gained in breaking into as many different sites as possible, in order to "launder" your connections.
Another reason may be psychological: some people love to play with computers and stretch them to the limits of their capabilities.
Some crackers might think that it's "really neat" to hop over 6 Internet machines, 2 gateways and an X.25 network just to knock on the doors of some really famous company or institution (eg: NASA, CERN, AT+T, UCB). Think of it as inter-network sightseeing.
This view is certainly appealing to some crackers, and certainly leads to both the addiction and self-perpetuation of cracking.
As to the "How" of the question, this is again a very sketchy area. In universities, it is extremely common for computer account to be passed back and forth between undergraduates:

      "Mary gives her account password to her boyfriend Bert at another
      site, who has a friend Joe who "plays around on the networks". Joe
      finds other crackable accounts at Marys site, and passes them around
      amongst his friends..." pretty soon, a whole society of crackers is
      playing around on the machines that Mary uses.
This sort of thing happens all the time, and not just in universities. One solution is in education. Do not let your users develop attitudes like this one:

      "It doesn't matter what password I use on _MY_ account,
      after all, I only use it for laserprinting..."
      - an Aberystwyth Law student, 1991
Teach them that use of the computer is a group responsibility. Make sure that they understand that a chain is only as strong as it's weak link.
Finally, when you're certain that they understand your problems as a systems manager and that they totally sympathise with you, configure your system in such a way that they can't possibly get it wrong.
Believe in user education, but don't trust to it alone.

Q.9 Who can I contact if I get broken into?
If you're connected to the Internet, you should certainly get in touch with CERT, the Computer Emergency Response Team.

      To quote the official blurb:
>From: Ed DeHart > The Computer Emergency Response Team (CERT) was formed by the Defense > Advanced Research Projects Agency (DARPA) in 1988 to serve as a focal > point for the computer security concerns of Internet users. The > Coordination Center for the CERT is located at the Software Engineering > Institute, Carnegie Mellon University, Pittsburgh, PA.
> Internet E-mail: cert@cert.org > Telephone: 412-268-7090 24-hour hotline: > CERT/CC personnel answer 7:30a.m. to 6:00p.m. EST(GMT-5)/EDT(GMT-4), > and are on call for emergencies during other hours.
...and also, the umbrella group "FIRST", which mediates between the incident handling teams themselves...
>From: John Wack >[...] FIRST is actually a very viable and growing >organization, of which CERT is a member. It's not actually true that, >if you're connected to the Internet, you should call CERT only - that >doesn't do justice to the many other response teams out there and in the >process of forming.
>NIST is currently the FIRST secretariat; we maintain an anonymous ftp >server with a directory of FIRST information (csrc.ncsl.nist.gov: >~/pub/first). This directory contains a contact file that lists the >current members and their constituencies and contact information >(filename "first-contacts").
>While CERT is a great organization, other response teams who do handle >incidents on their parts of the Internet merit some mention as well - >perhaps mentioning the existence of this file would help to do that in a >limited space.
The file mentioned is a comprehensive listing of contact points per network for security incidents. It is too large to reproduce here, I suggest that the reader obtains a copy for his/her self by the means given.

Q.10 What is a firewall?
A (Internet) firewall is a machine which is attached (usually) between your site and a wide area network. It provides controllable filtering of network traffic, allowing restricted access to certain internet port numbers (ie: services that your machine would otherwise provide to the network as a whole) and blocks access to pretty well everything else. Similar machines are available for other network types, too.
Firewalls are an effective "all-or-nothing" approach to dealing with external access security, and they are becoming very popular, with the rise in Internet connectivity.
For more information on these sort of topics, see the Gateway paper by [Cheswick], below.

Q.11 Why shouldn't I use setuid shell scripts?
You shouldn't use them for a variety of reasons, mostly involving bugs in the Unix kernel. Here are a few of the more well known problems, some of which are fixed on more recent operating systems.
1) If the script begins "#!/bin/sh" and a link (symbolic or otherwise) can be made to it with the name "-i", a setuid shell can be immediately obtained because the script will be invoked: "#!/bin/sh -i", ie: an interactive shell.
2) Many kernels suffer from a race condition which can allow you to exchange the shellscript for another executable of your choice between the times that the newly exec()ed process goes setuid, and when the command interpreter gets started up. If you are persistent enough, in theory you could get the kernel to run any program you want.
3) The IFS bug: the IFS shell variable contains a list of characters to be treated like whitespace by a shell when parsing command names. By changing the IFS variable to contain the "/" character, the command "/bin/true" becomes "bin true".
All you need do is export the modified IFS variable, install a command called "bin" in your path, and run a setuid script which calls "/bin/true". Then "bin" will be executed whilst setuid.
If you really must write scripts to be setuid, either

      a) Put a setuid wrapper in "C" around the script, being very careful
      to reset IFS and PATH to something sensible before exec()ing the
      script. If your system has runtime linked libraries, consider the
      values of the LD_LIBRARY_PATH also.

      b) Use a scripting language like Perl which has a safe setuid
      facility, and is proactively rabid about security.
- but really, it's safest not to use setuid scripts at all.

Q.12 Why shouldn't I leave "root" permanently logged on the console?
Using a 'smart' terminal as console and leaving "/dev/console" world writable whilst "root" is logged in is a potential hole. The terminal may be vulnerable to remote control via escape sequences, and can be used to 'type' things into the root shell. The terminal type can usually be obtained via the "ps" command.
Various solutions to this can be devised, usually by giving the console owner and group-write access only , and then using the setgid mechanism on any program which has need to output to the console (eg: "write").

Q.13 Why shouldn't I create Unix accounts with null passwords?
Creating an unpassworded account to serve any purpose is potentially dangerous, not for any direct reason, but because it can give a cracker a toehold.
For example, on many systems you will find a unpassworded user "sync", which allows the sysman to sync the disks without being logged in. This appears to be both safe and innocuous.
The problem with this arises if your system is one of the many which doesn't do checks on a user before authorising them for (say) FTP. A cracker might be able to connect to your machine for one of a variety of FTP methods, pretending to be user "sync" with no password, and then copy your password file off for remote cracking.
Although there are mechanisms to prevent this sort of thing happening in most modern vesions of Unix, to be totally secure requires an in-depth knowledge of every package on your system, and how it deals with the verification of users. If you can't be sure, it's probably better not to leave holes like this around.
Another hole that having null-password accounts opens up is the possibility (on systems with runtime linked libraries) of spoofing system software into running your programs as the "sync" user, by changing the LD_LIBRARY_PATH variable to a library of your own devising, and running "login -p" or "su" to turn into that user.

>From: chowes@sfu.ca > >Don't forget LD_LIBRARY_PRELOAD! You can point it to a library that >contains routines to override LD_LIBRARY_PATH routines. Main advantage >is that the library is a lot smaller by virtue of only having the >doctored routines, not *every* routine; and also that some people >forget to protect both.
[Just how many more of these LD_* variables ARE there ? - Alec]

>From: barnett@alydar.crd.ge.com (Bruce Barnett) > >One more thing you may want to mention is that each network service must >be checked to see if there is any security problem. Not all services >use the shell entry in a passwd file. Therefore having a null password >make allow other services to break into the account. > >For instance, some systems that provide remote file access uses the >username and password to verify access. The shell entry is not used. > >Therefore it is possible for someone to use the "sync" account to >"mount" a Unix file system, getting access to the account without using >the shell. > >To be precise, I used Sun's TOPS service on a Macintosh to mount a Unix >file system thru the sync account as it didn't have any password. I has >user ID "1" when I did this. Don't know if this needs to be added to >the FAQ... I did notify Sun a while ago about this bug....

Q.14 What security holes are associated with X-windows (and other WMs)?
Lots, some which affect use of X only, and some which impact the security of the entire host system.
I would prefer not to go into too much detail here, and would refer any reader reader looking for detailed information to the other FAQ's in relevant newsgroups. (comp.windows.*)
One point I will make is that X is one of those packages which often generates "Incompatible Usage" security problems, for instance the ability for crackers to run xsessions on hosts under accounts with no password (eg: sync), if it is improperly set up. Read the question about unpassworded accounts in this FAQ.

Q.15 What security holes are associated with NFS?
Lots, mostly to do with who you export your disks to, and how. The security of NFS relies heavily upon who is allowed to mount the files that a server exports, and whether they are exported read only or not.
The exact format for specifying which hosts can mount an exported directory varies between Unix implementations, but generally the information is contained within the file "/etc/exports".
This file contains a list of directories and for each one, it has a series of either specific "hosts" or "netgroups" which are allowed to NFS mount that directory. This list is called the "access list".
The "hosts" are individual machines, whilst "netgroups" are combinations of hosts and usernames specified in "/etc/netgroup". These are meant to provide a method of finetuning access. Read the relevant manual page for more information about netgroups.
The exports file also contains information about whether the directory is to be exported as read-only, read-write, and whether super-user access is to be allowed from clients which mount that directory.
The important point to remember is that if the access list for a particular directory in /etc/exports contains:
1)
Your directory can be mounted by anyone, anywhere.
2)
Your directory can be mounted by anyone permitted to run the mount command at hostname. This might not be a trustworthy person; for instance, if the machine is a PC running NFS, it could be anyone.
3)

If the netgroup:
a) is empty, anyone can mount your directory, from anywhere.
b) contains "(,,)", anyone can mount your directory, from anywhere.
c) contains the name of a netgroup which is empty or contains "(,,)",
      anyone can mount your directory, from anywhere.
d) contains "(hostname,,)", anyone on the named host who is permissioned
      to mount files can mount your directory.
e) contains "(,username,)", the named user can mount your directory,
      from anywhere.
4)

If you meant to export the directory to the host "athena" but actually type "ahtena", the word "ahtena" is taken as a netgroup name, is found to be an empty netgroup, and thus the directory can be mounted by anyone, anywhere.
So, if you aren't careful about what you put into /etc/exports and /etc/netgroup you could find that a user with a PC could

      a) mount your mainframe filestore as a network disk
      b) edit your /etc/passwd or .rhosts or /etc/hosts.equiv ...
      c) log into your mainframe as another user, possibly "root"
Disclaimer: The above information may not be true for all platforms which provide an NFS serving capability, but is true for all of the ones in my experience (Alec). It should be noted that the SAFE way to create an "empty" netgroup entry is:

      ngname (-,-,-)
Which is a netgroup which matches no-one on no-host on no-NIS-domain.
>From: Mark Crispin > >NFS is far more insecure than the FAQ implies. It does not require >any carelessness in export files, since the only thing the export file >does is be helpful in disclosing the key that an NFS client needs to >unlock your system. Means exist to guess these keys. It is prudent, >to say the least, to configure your routers to forbid NFS traffic from >outside your organization.
[...this is true; I just haven't had time to document it yet...]

Q.16 How can I generate safe passwords?
You can't. The key word here is GENERATE. Once an algorithm for creating passwords is specified using upon some systematic method, it merely becomes a matter of analysing your algorithm in order to find every password on your system.
Unless the algorithm is very subtle, it will probably suffer from a very low period (ie: it will soon start to repeat itself) so that either:

      a) a cracker can try out every possible output of the password
      generator on every user of the system, or

      b) the cracker can analyse the output of the password program,
      determine the algorithm being used, and apply the algorithm to other
      users to determine their passwords.
A beautiful example of this (where it was disastrously assumed that a random number generator could generate an infinite number of random passwords) is detailed in [Morris & Thompson].
The only way to get a reasonable amount of variety in your passwords (I'm afraid) is to make them up. Work out some flexible method of your own which is NOT based upon:

      1) modifying any part of your name or name+initials
      2) modifying a dictionary word
      3) acronyms
      4) any systematic, well-adhered-to algorithm whatsoever
For instance, NEVER use passwords like:
alec7 - it's based on the users name (& it's too short anyway) tteffum - based on the users name again gillian - girlfiends name (in a dictionary) naillig - ditto, backwards PORSCHE911 - it's in a dictionary 12345678 - it's in a dictionary (& people can watch you type it easily) qwertyui - ...ditto... abcxyz - ...ditto... 0ooooooo - ...ditto... Computer - just because it's capitalised doesn't make it safe wombat6 - ditto for appending some random character 6wombat - ditto for prepending some random character merde3 - even for french words... mr.spock - it's in a sci-fi dictionary zeolite - it's in a geological dictionary ze0lite - corrupted version of a word in a geological dictionary ze0l1te - ...ditto... Z30L1T3 - ...ditto...
I hope that these examples emphasise that ANY password derived from ANY dictionary word (or personal information), modified in ANY way, constitutes a potentially guessable password.
For more detailed information in the same vein, you should read the APPENDIX files which accompany Crack [Muffett].

Q.17 Why are passwords so important?
Because they are the first line of defence against interactive attacks on your system. It can be stated simply: if a cracker cannot interact with your system(s), and he has no access to read or write the information contained in the password file, then he has almost no avenues of attack left open to break your system.
This is also why, if a cracker can at least read your password file (and if you are on a vanilla modern Unix, you should assume this) it is so important that he is not able to break any of the passwords contained therein. If he can, then it is also fair to assume that he can (a) log on to your system and can then (b) break into "root" via an operating system hole.

Q.18 How many possible passwords are there?
Most people ask this at one time or another, worried that programs like Crack will eventually grow in power until they can do a completely exhaustive search of all possible passwords, to break into a specific users' account - usually root.
If (to simplify the maths) we make the assumptions that:

      1) Valid passwords are created from a set of 62 chars [A-Za-z0-9]
      2) Valid passwords are to be between 5 and 8 chars long
Then the size of the set of all valid passwords is: (in base 62)

      100000b62 +
      1000000b62 +
      10000000b62 +
      100000000b62 =

      111100000b62

      ~= 222000000000000 (decimal)
A figure which is far too large to usefully undertake an exhaustive search with current technologies. Don't forget, however, that passwords CAN be made up with even more characters then this; you can use , all the punctuation characters, and symbols (~<>|\#$%^&*) too. If you can use some of all the 95 non-control characters in passwords, this increases the search space for a cracker to cover even further.
However, it's still MUCH more efficient for a cracker to get a copy of "Crack", break into ANY account on the system (you only need one), log onto the machine, and spoof his way up to root priviledges via operating systems holes.
Take comfort from these figures. If you can slam the door in the face of a potential crackers with a robust password file, you have sealed most of the major avenues of attack immediately.

Q.19 Where can I get more information?
Books:
[Kochan & Wood] Unix System Security
A little dated for modern matters, but still a very good book on the basics of Unix security.
[Spafford & Garfinkel] Practical Unix Security
This wonderful book is a worthy successor to the above, and covers a wide variety of the topics which the Unix (and some non Unix) system manager of the 90's will come across.
>From: Gene Spafford >Mention appendix E in "Practical Unix Security."
Okay: Appendix E contains an extensive bibliography with even more pointers to security books than this FAQ contains.
[Stoll] The Cuckoo's Egg
A real life 1980's thriller detailing the tracing of a cracker from Berkeley across the USA and over the Atlantic to Germany. An excellent view from all points: a good read, informative about security, funny, and a good illustration of the cracker psyche. Contains an excellent recipie for chocolate chip cookies.
A videotape of the "NOVA" (PBS's Science Program on TV) episode that explained/reenacted this story is available from PBS Home Video. They have a toll-free 800 number within North America.
I believe that this program was aired on the BBC's "HORIZON" program, and thus will be available from BBC Enterprises, but I haven't checked this out yet - Alec
THE TECHNICAL PAPER containing details of the "Cuckoo's Egg" breakin is called "Stalking the wily hacker" in an issue of CACM which I will dig out and get the proper reference for, in my copious free time - Alec

[Raymond] (Ed.) The New Hackers Dictionary/Online Jargon File
A mish-mash of history and dictionary definitions which explains why it is so wonderful to be a hacker, and why those crackers who aren't hackers want to be called "hackers". The Jargon File version is available online - check an archie database for retails. Latest revision: 3.00.
[Gasser] Building a Secure Computer System.
By Morrie Gasser, and van Nostrand Reinhold; explains what is required to build a secure computer system.
[Rainbow Series] (Especially the "Orange Book")
>From: epstein@trwacs.fp.trw.com (Jeremy Epstein) >The "Rainbow Series" consists of about 25 volumes. Some of the >more interesting ones are: > > The "Orange Book", or Trusted Computer Systems Evaluation > Criteria, which describes functional and assurance > requirements for computer systems > > Trusted Database Interpretation, which talks both about > trusted databases and building systems out of trusted > components > > Trusted Network Interpretation, which (obviously) talks > about networked systems > >A (possibly) complete list is: > -- Department of Defense Trusted Computer System Evaluation Criteria > (TCSEC), aka the "Orange Book" > -- Computer Security Subsystem Interpretation of the TCSEC > -- Trusted Data Base Management System Interpretation of the TCSEC > -- Trusted Network Interpretation of the TCSEC > -- Trusted Network Interpretation Environments Guideline -- Guidance > for Applying the Trusted Network Interpretation > -- Trusted Unix Working Group (TRUSIX) Rationale for Selecting > Access Control List Features for the Unix System > -- Trusted Product Evaulations -- A Guide for Vendors > -- Computer Security Requirements -- Guidance for Applying the DoD > TCSEC in Specific Environments > -- Technical Rationale Behind CSC-STD-003-85: Computer Security > Requirements > -- Trusted Product Evaluation Questionnaire > -- Rating Maintenance Phase -- Program Document > -- Guidelines for Formal Verification Systems > -- A Guide to Understanding Audit in Trusted Systems > -- A Guide to Understanding Trusted Facility Management > -- A Guide to Understanding Discretionary Access Control in Trusted > Systems > -- A Guide to Understanding Configuration Management in Trusted Systems > -- A Guide to Understanding Design Documentation in Trusted Systems > -- A Guide to Understanding Trusted Distribution in Trusted Systems > -- A Guide to Understanding Data Remanence in Automated Information > Systems > -- Department of Defense Password Management Guideline > -- Glossary of Computer Security Terms > -- Integrity in Automated Information Systems > >You can get your own copy (free) of any or all of the books by >writing or calling: > > INFOSEC Awareness Office > National Computer Security Centre > 9800 Savage Road > Fort George G. Meade, MD 20755-6000 > >If you ask to be put on the mailing list, you'll get a copy of each new >book as it comes out (typically a couple a year).
>From: kleine@fzi.de (Karl Kleine) >I was told that this offer is only valid for US citizens ("We only send >this stuff to a US postal address"). Non-US people have to PAY to get >hold of these documents. They can be ordered from NTIS, the National >Technical Information Service: > NTIS, > 5285 Port Royal Rd, > Springfield VA 22151, > USA
>From: Ulf Kieber >just today I got my set of the Rainbow Series. > >There are three new books: > -- A Guide to Understanding Trusted Recovery in Trusted Systems > -- A Guide to Understanding Identification and Authentication in Trusted > Systems > -- A Guide to Writing the Security Features User's Guide for Trusted Systems > >They also shipped > -- Advisory Memorandum on Office Automation Security Guideline >issued by NTISS. Most of the books (except three or four) can also be >purchased from > > U.S. Government Printing Office > Superintendent of Documents > Washington, DC 20402 phone: (202) 783-3238 > >>-- Integrity in Automated Information Systems >THIS book was NOT shipped to me--I'm not sure if it is still in >the distribution.
>From: epstein@trwacs.fp.trw.com (Jeremy Epstein) >... >The ITSEC (Information Technology Security Evaluation Criteria) is a >harmonized document developed by the British, German, French, and >Netherlands governments. It separates functional and assurance >requirements, and has many other differences from the TCSEC. > >You can get your copy (again, free/gratis) by writing: > > Commission of the European Communities > Directorate XIII/F > SOG-IS Secretariat > Rue de la Loi 200 > B-1049 BRUSSELS > Belgium
>From: Nick Barron > >...The ITSEC and associated DTI security publications (the "Green >Books") are available for *free* (makes a change) from the DTI >Commercial Computer Security Centre. The contact is Fiona Williams on >081 977 3222 or as fjw@dsg.npl.co.uk. Hope that this is of interest. >The ITSEC is currently being "harmonised" with the Orange Book...
Also note that NCSC periodically publish an "Evaluated Products List" which is the definitive statement of which products have been approved at what TCSEC level under which TCSEC interpretations. This is useful for separating the output of marketdroids from the truth.

Papers:
[Morris & Thompson] Password Security, A Case History
A wonderful paper, first published in CACM in 1974, which is now often to found in the Unix Programmer Docs supplied with many systems.
[Curry] Improving the Security of your Unix System.
A marvellous paper detailing the basic security considerations every Unix systems manager should know. Available as "security-doc.tar.Z" from FTP sites (check an Archie database for your nearest site.)
[Klein] Foiling the Cracker: A Survey of, and Improvements to, Password Security.
A thorough and reasoned analysis of password cracking trends, and the reasoning behind techniques of password cracking. Your nearest copy should be easily found via Archie, searching for the keyword "Foiling".
[Cheswick] The Design of a Secure Internet Gateway.
Great stuff.
Host: research.att.com Location: dist/internet_security

      FILE rw-rw-r-- 33836 Jul 24 1992 gateway.dvi
      FILE rw-rw-r-- 42373 Aug 19 1991 gateway.ps
      FILE rw-rw-r-- 674169 Jun 28 12:23 gateway_slides.ps
[Cheswick] An Evening With Berferd: in which a Cracker is Lured, Endured & Studied.
Funny and very readable, somewhat in the style of [Stoll] but more condensed.
Host: research.att.com Location: dist/internet_security

      FILE rw-rw-r-- 41612 Jul 24 1992 berferd.dvi
      FILE rw-rw-r-- 81747 Jul 24 1992 berferd.ps
[Bellovin89] Security Problems in the TCP/TP Protocol Suite.
A description of security problems in many of the protocols widely used in the Internet. Not all of the discussed protocols are official Internet Protocols (i.e. blessed by the IAB), but all are widely used. The paper originally appeared in ACM Computer Communications Review, Vol 19, No 2, April 1989.
Host: research.att.com Location: dist/internet_security

      FILE rw-rw-r-- 48703 Aug 22 1991 ipext.ps.Z
[Bellovin91] Limitations of the Kerberos Authentication System
A discussion of the limitations and weaknesses of the Kerberos Authentication System. Specific problems and solutions are presented. Very worthwhile reading. Available on research.att.com via anonymous ftp, originally appeared in ACM Computer Communications Review but the revised version (identical to the online version, I think) appeared in the Winter 1991 USENIX Conference Proceedings.
[Muffett] Crack documentation.
The information which accompanies Crack contains a whimsical explanation of password cracking techniques and the optimisation thereof, as well as an incredibly long and silly diatribe on how to not choose a crackable password. A good read for anyone who needs convincing that password cracking is _really easy_.
[Farmer] COPS
Read the documentation provided with COPS. Lots of hints and philosophy. The where, why and how behind the piece of security software that started it all.
[CERT] maillists/advisories/clippings
CERT maintains archives of useful bits of information that it gets from USENET and other sources. Also archives of all the security "advisories" that it has posted (ie: little messages warning people that there is a hole in their operating system, and where to get a fix)
[OpenSystemsSecurity]
A notorious (but apparently quite good) document, which has been dogged by being in a weird postscript format.
>From: amesml@monu1.cc.monash.edu.au (Mark L. Ames)
>I've received many replies to my posting about Arlo Karila's paper, >including the news (that I and many others have missed) that a >manageable postscript file and text file are available via anonymous ftp >from ajk.tele.fi (131.177.5.20) in the directory PublicDocuments.
These are all available for FTP browsing from "cert.org".
[RFC-1244] Site Security Handbook
RFC-1244 : JP Holbrook & JK Reynolds (Eds.) "The Site Security Handbook" covering incident handling and prevention. July 1991; 101 pages (Format: TXT=259129 bytes), also called "FYI 8"
[USENET] comp.virus: for discussions of virii and other nasties, with a PC bent. comp.unix.admin: for general administration issues comp.unix.: for the hardware/software that YOU use. comp.protocols.tcp-ip: good for problems with NFS, etc.

Q.20 How silly can people get?
This section (which I hope to expand) is a forum for learning by example; if people have a chance to read about real life (preferably silly) security incidents, it will hopefully instill in readers some of the zen of computer security without the pain of experiencing it.
If you have an experience that you wish to share, please send it to the editors. It'll boost your karma no end.
From: aem@aber.ac.uk
The best story I have is of a student friend of mine (call him Bob) who spent his industrial year at a major computer manufacturing company. In his holidays, Bob would come back to college and play AberMUD on my system.
Part of Bob's job at the company involved systems management, and the company was very hot on security, so all the passwords were random strings of letters, with no sensible order. It was imperative that the passwords were secure (this involved writing the random passwords down and locking them in big, heavy duty safes).
One day, on a whim, I fed the MUD persona file passwords into Crack as a dictionary (the passwords were stored plaintext) and then ran Crack on our systems password file. A few student accounts came up, but nothing special. I told the students concerned to change their passwords - that was the end of it.
Being the lazy guy I am, I forgot to remove the passwords from the Crack dictionary, and when I posted the next version to USENET, the words went too. It went to the comp.sources.misc moderator, came back over USENET, and eventually wound up at Bob's company. Round trip: ~10,000 miles.
Being a cool kinda student sysadmin dude, Bob ran the new version of Crack when it arrived. When it immediately churned out the root password on his machine, he damn near fainted...
The moral of this story is: never use the same password in two different places, and especially on untrusted systems (like MUDs).
From: zerkle@cs.ucdavis.edu (Dan Zerkle)
I've got a good one.
Our department has a room of workstations for graduate students who have not started on a research project. If you don't have an account, you can still use these workstations as terminals. There is a special, null-password account called "terminal". This account runs a short program which accepts a machine name, a user name and a password, then runs rlogin to connect you to the machine of your choice.
Awhile back, I used this system, but accidentally hit RETURN before I typed my user name. Since there was no way to back out, I also hit RETURN for the password.
As it happened, the machine to which I was connecting had an entry in the password file like this:
::0:1::: (this is a YP/NIS password entry, missing a "+" symbol)
You can imagine how startled I was when the terminal program connected me and logged me in as root! I sent mail to the system administrator (as root, just to irk him), and got the hole patched within a day.
Ordinarily, the entry in the password file was not a problem. Normal methods of logging in require you to supply a user name. However, the "terminal" login accepted the null string as a user name and passed it on (via rlogin) to the host computer. Thus, purely by accident, I managed to break root on that machine.

      -Dan
From: BENNETT@dstos3.dsto.gov.au (John Bennett)
Hi Alec,
You asked for contributions for "How silly can people get ?" Here is a simple but true and possibly oft repeated story...
My son bought a new car, so we went down to the local office of the Royal Automobile Association to insure it. A Charming Young Lady was very helpful and efficient as we sorted out the details of the policy. Once the paperwork was written, the CYL went across the office to a computer terminal, sat down, and called to another CYL
"Is the password still (censored, name of computer company) ?".
Regards,
John Bennett bennett@dstos3.dsto.gov.au
From: Alec.Muffett@UK.Sun.COM
- A cautionary tale, about a friend of mine who will probably wish to
      remain anonymous, for his sins. (Hi, Ian!)
At a British university with a particularly paranoid (not to say rabid) security policy, the systems administrators had changed the permissions on the "su" command, removing world execute permission, and making it group-execute only to members of the computing services staff.
...however, the staff were not informed enough to remove world-write permission from /dev/console.
My friend, Ian, attended this university, and on one occasion became particularly annoyed at a fellow student-user (let's call him foobar1).
Foobar1 was apparently nosing round the terminals of everyone in the room, peering over the shoulders of his fellow students, and not obeying the rules of etiquette.
So, in order to "get him back", Ian did this:
Ian wrote a script which, every so often, would print:

      BAD SU: foobar1 on tty0a at 12:34:56
- to the machine's console.
Given that "only members of staff can use 'su' to get to root on this system", this must have worried the operators mightily.
After a few iterations of this cat-and-mouse game, Ian did:

      SU: foobar1 on tty0a at 12:45:03
- thirty seconds later, the machine crashed. The operations team, rather than let this horrible hacker run amok on the system, chose to pull the plug. They then arrived in the terminal room, hauled "foobar1" out backwards, took him away and shouted at him for an hour or so, until they believed that it wasn't him.
I believe that Ian apologised to foobar1 eventually, but the systems people never *did* sort it out. The moral of this tale?
During an incident:

      1) don't panic - you might do something stupid
      2) don't trust any audit trail which is open to compromise
Alec Muffett (alec.muffett@sun.co.uk) Sun Microsystems IR, Bagshot, Surrey, UK
      #include





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