Computer Emergency Response - An International
Problem8|-
9 Richard D. Pethia
Kenneth R. van Wyk
Computer Emergency Response Team / Coordination Center
Software Engineering Institute
Carnegie Mellon University
4500 Fifth Avenue
Pittsburgh, PA 15213-3890
U.S.A.
_A_B_S_T_R_A_C_T
Computer security incidents during the past
few years have illustrated that unauthorized com-
puter activity does not obey traditional boun-
daries (e.g., national, network, computer archi-
tecture). Instead, such activity frequently
crosses these boundaries not just once, but
several times per incident [Stoll89].
International cooperation among computer security
response groups can be an effective means of deal-
ing with computer security issues faced today by
the computer user community. This paper addresses
the need for such cooperation and suggests methods
by which individual computer security response
groups can work together internationally to cope
with computer security incidents.
_1. _B_a_c_k_g_r_o_u_n_d
The increasing use and dependence on interconnected local,
regional, and wide area networks, while bringing important
new capabilities, also brings new vulnerabilities. Widely
publicized events such as the November 1988, Internet Worm,
which affected thousands of systems on the international
research network Internet, or the October 1989, WANK worm,
which affected hundreds of systems on NASA's Space Physics
and Analysis (SPAN) network are unusual, although dramatic,
events. There are many more events such as intrusions,
exploitation of vulnerabilities, and discovery of new
_________________________
9 |= Sponsored by the U.S. Department of Defense
9
November 14, 1990
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vulnerabilities that occur with much greater frequency and
require effective methods of response. Several examples are
listed below.
_1._1. _I_n_c_i_d_e_n_t_s
From August 1986 until late 1987, staff members at Lawrence
Berkeley Laboratory worked with investigators to trace the
paths of a computer intruder; the trail eventually lead them
to a KGB-funded intruder operating out of Hannover, Germany
[Stoll88]. The investigation was often hampered by a lack
of cooperation among "bureaucratic organizations" [Stoll88].
On the other hand, "cooperation between system managers,
communications technicians, and network operators was excel-
lent" [Stoll88]. Still, it was only when the investigators
in both countries got involved that the intruder was
apprehended [Stoll89]. It is worthwhile to note that the
break-ins in this case utilized the same attack methods over
and over (such as repeatedly guessing common and system
default username/password combinations, exploiting well
known security holes which had not yet been fixed by the
system administrators, etc.); through diligent, methodical
application of these methods, the intruders were successful
at entering dozens of computer systems [Stoll89].
In November 1988, a rogue worm program entered the Internet
and caused widespread system failures [Spafford88]. The
worm, written by Cornell University graduate student Robert
Tappan Morris, Jr. [Markoff90a], exploited lax password pol-
icies as well as two software implementation errors in
specific versions of UNIX, the predominant operating system
on Internet computers.
More recently, three Australian computer intruders were
arrested by Australian Federal police "after a two-year
investigation that included cooperation with United States
authorities" [Markoff90b]. Again, the intruders exploited
known vulnerabilities to gain unauthorized entry onto sys-
tems [Danca90].
In October 1989, a worm program called Worms Against Nuclear
Killers (WANK) infected a National Aeronautics and Space
Administration (NASA) network [Alexander89]. The worm pro-
gram spread to many computers in different countries by
using system vulnerabilities that "should have been closed
months ago" following a similar incident in December 1988
[Alexander89].
In another, albeit domestic, case, two computer intruders
were arrested and charged with illegal use of computer sys-
tems at Pennsylvania State University. The intrusions took
place on a computer system at the University of Chicago.
University of Chicago officials contacted CERT/CC, which
then contacted administrators at Penn State. Eventually,
November 14, 1990
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through the cooperation of the administrators and investiga-
tors, the two Penn State students were charged [Graf90].
These cases all illustrate the need for cooperation among
computer security response groups.
_1._2. _S_y_s_t_e_m _V_u_l_n_e_r_a_b_i_l_i_t_i_e_s
Another situation in which cooperation across multiple
organizations becomes essential is in dissemination of sys-
tem vulnerability alerts (and, more importantly, their solu-
tions). As system intruders successfully gain access to
systems which have weak passwords or systems where known
security vulnerabilities have not been closed, they often
share information on vulnerabilities in these systems with
others. Likewise, as intruders discover new vulnerabilities
in particular operating system or other software packages,
information on the vulnerabilities is quickly communicated
through various bulletin boards and other electronic forums.
As a result, many large communities of system users quickly
become vulnerable. Traditional methods of dealing with vul-
nerability information, including closely protecting infor-
mation on the existence of the vulnerability, are not effec-
tive once intruders have learned of system weaknesses. In
these cases, supplying password guideline and security vul-
nerability information to system administrators is crucial
in raising security levels and deterring attacks.
The Computer Emergency Response Team Coordination Center
(CERT/CC) (see Section 2.1) frequently distributes CERT
Advisories that, among other things, inform the public of
vulnerabilities, fixes, and active methods of attack.
_2. _E_m_e_r_g_e_n_c_y _R_e_s_p_o_n_s_e _G_r_o_u_p_s
_2._1. _I_n_t_r_o_d_u_c_t_i_o_n _t_o _C_E_R_T
Shortly after the Internet worm of November 1988 [Spaf-
ford88], the Defense Advanced Research Projects Agency
(DARPA) started the Computer Emergency Response Team (CERT),
whose Coordination Center (CERT/CC) is located at Carnegie
Mellon University's Software Engineering Institute (SEI)
[Scherlis88]. "The CERT is a community group intended to
facilitate community response to computer security events
involving Internet hosts" [Denning90]. CERT consists of
hundreds of highly qualified volunteers throughout the com-
puter community, as well as the staff of the CERT/CC and of
the other emergency response groups in the CERT-System (see
Section 2.2 for details). The CERT/CC serves as a focal
point for response to Internet computer security problems
[Denning90]. Since it would be impossible for any one
response group to address the needs of all constituencies|=,
_________________________
November 14, 1990
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the need for multiple CERT groups exists. (This issue, too,
is covered in more detail in Section 2.2.)
CERT groups must have sufficient in-house technical exper-
tise to handle a reasonable portion of day to day security
incidents, leaving the volunteer contacts for situations
which require additional expertise. However, because emer-
gency response involves addressing more than just technical
issues, CERT membership includes not only technical experts,
but site managers, security officers, industry representa-
tives, and government officials [Denning90].
One of the essential characteristics of a CERT group is
being available to its constituency on a 24 hour per day
basis. There must be a well publicized central point of
contact which is available continuously. This should
include, at a minimum, a "hotline" telephone which is con-
stantly manned, and an electronic mailbox which is monitored
during business hours. The CERT/CC hotline number is (412)
268-7090, and its electronic mailbox address is
cert@cert.sei.cmu.edu, on the Internet.
It is critical that a CERT group build and maintain a col-
lection of contacts, both within the group's constituency
and externally [Dalton90]. The contact information should
include other CERT groups, system vendors, law enforcement,
network operation centers, technical experts, site adminis-
trators, etc. Building the contact information is an on-
going process in which contacts are developed and maintained
over time. Each contact must be aware of its responsibili-
ties and/or expectations in the emergency response process
[Dalton90].
In addition to the contact information, a CERT group should
maintain an information repository which will be drawn upon
in future incidents. The information in the repository will
include contact information (as detailed above), system vul-
nerability details, security incident reports, electronic
mail archives, and other relevant information [Denning90].
Due to the nature of this information, the security on the
system on which it resides must be beyond reproach. CERT/CC
maintains its information database on an off-line system,
which is not accessible via network connections.
As system vulnerabilities (and their fixes), break-in warn-
ing information, and other relevant information becomes
available, CERT groups should issue advisories to members of
their constituency [Denning90]. Past CERT/CC advisories
have included vulnerability notification (along with
appropriate solutions), warnings of widespread break-ins and
_________________________
|= The term "constituency" is used here to define a
group with some common needs.
November 14, 1990
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symptoms thereof, and secure system administration sugges-
tions. The entire collection of CERT/CC advisories are
maintained on-line and are accessible to CERT/CC consti-
tuents.
_2._1._1. _E_x_a_m_p_l_e _C_E_R_T _I_n_c_i_d_e_n_t _H_a_n_d_l_i_n_g _P_r_o_c_e_d_u_r_e_s
As an ongoing process, CERT/CC has developed and is continu-
ing to improve upon its event handling procedures. Natur-
ally, the procedures are different for each distinct type of
event (e.g., system break-in, vulnerability report, worm).
This section presents an overview of some of these pro-
cedures.
When CERT/CC receives a report of a system break-in, it
first works together with the affected system
administrator(s) in determining how the intruder gained
access to the system. This is generally in the form of
offering guidance on what sort of signs the administrator
should look for to determine means of access. Next, CERT/CC
offers assistance in repairing the exploited hole(s), as
well as other commonly known vulnerabilities. Examining
systems for backdoors or trojan horses that have been
planted by the intruder is an especially important activity.
If the break-in came from other sites, or if the intruder
broke into other systems from the current system, CERT/CC
notifies other affected site administrators (from time to
time, the administrator will already have contacted other
affected sites; in such a case, CERT/CC requests to be kept
up to date with the relevant flow of information between the
sites). In some cases, other affected, or potentially
affected, sites are not Internet sites. In these cases,
communication across traditional "territorial" boundaries is
especially important. It is important to note that, when
contacting sites, CERT/CC always maintains the confidential-
ity of the affected sites unless the sites specify other-
wise.
As system vulnerabilities are reported to CERT/CC, they are
first authenticated and then reported to the affected
vendor(s). CERT/CC offers guidance to the vendor community
by reporting the magnitude of the threat (e.g., whether the
hole is being actively exploited, whether the hole is known
to a widespread audience, whether the hole can be exploited
from a remote system or requires existing system access in
order to be exploited). CERT/CC also offers technical
input, if desired by the vendors. The vendor community will
generally respond with a fix, a workaround, or a reference
to same for the problem. In many cases, the CERT/CC has
received advanced versions of fixes from vendors and has
received the vendor's authorization to release the fix to
selected members of the technical community for review and
comment. This technical review process shows promise of
improving the quality of corrections to vulnerabilities.
November 14, 1990
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Depending upon the situation, CERT/CC then drafts an
advisory for review by the vendors, the CERT-System, and/or
technical affiliates. When the draft advisory is mutually
accepted, it is distributed electronically to CERT/CC's con-
stituency, the Internet research community. For this,
CERT/CC operates a CERT Advisory mailing list, in addition
to a Usenet newsgroup, comp.security.announce [Quarter-
man90]. (See Appendix 1 for an example CERT/CC advisory.)
_2._2. _C_E_R_T-_S_y_s_t_e_m
As mentioned in Section 2.1, no single emergency response
group can be expected to address the needs of every portion
of the computing world, due to the diversities and scale of
all of the various computing environments [Denning90].
Individual communities each have their own distinct poli-
cies, rules, regulations, procedures, and culture. Methods
effective in one community (e.g., the Internet research com-
munity) would not likely succeed in other communities that
have significantly different cultures (e.g., the military
community or the banking community).
In addition, implementation platforms (operating systems,
networking software and protocols) vary widely. A single
CERT group would not likely be successful in dealing with
technical diversity, or at least could not do so economi-
cally.
The "CERT-System" model, therefore, includes multiple,
cooperating individual CERT organizations. Each individual
CERT group in the CERT-System focuses on a particular con-
stituency.
Each constituency in the model can be defined by either user
or technology boundaries. The user constituencies consist
of groups with common networks, needs, and/or policies,
while the technology constituencies are groups with common
computing architectures [Denning90]. An example of a user
constituency is the Internet research community, which is
made up of organizations in academia, government, military,
as well as commercial groups. These groups are bound
together by being members of the Internet network. An exam-
ple technology constituency is the IBM mainframe community,
which is bound by a common computer architecture.
The CERT/CC group addresses both a user constituency (Inter-
net research community) and a technology constituency
(UNIX-based workstations and mainframes, which is the pri-
mary type of system on the Internet).
The CERT model lends itself well to network groups such as
the Internet research community, as well as corporate
[Fedeli90], government, military, etc., groups.
November 14, 1990
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In times of crisis, many CERT groups can be active with a
technology coordination center analyzing problems and coor-
dinating the search for solutions and with user constituency
coordination centers gathering information and informing
their constituents as appropriate.
In less troubled times, the CERTs work together to build
effective communication mechanisms, share information on
effective computer security tools and techniques, and con-
duct proactive campaigns aimed at increasing the awareness
of computer security issues and improving the security of
operational systems.
The CERT-System model has been widely accepted and eleven
groups funded by U.S. government agencies and several
private firms now participate in the system. Interest in
participating has been expressed by several other organiza-
tions and steps are being taken to more formally structure
the CERT-System. This structure, including a charter and
by-laws that are being reviewed and approved by existing
CERT-System members as this paper is being written, will
provide a framework to enable wider participation.
_3. _C_o_n_c_l_u_s_i_o_n_s
It has been shown that the CERT concept can be an effective
means of responding to computer security-related incidents
[Graf90]. In incidents prior to the existence of CERT,
system administrators were frequently at a loss for outside
assistance when handling security incidents
[Stoll88,Stoll89]. It has also been shown that computer
system security incidents do not obey network, national, or
architectural boundaries [Stoll88] and that the intruders
frequently exploit lax security procedures (due, perhaps, to
a lack of specific knowledge on the administrators' part)
[Stoll88,Danca90,Alexander89].
Effective computer security incident response requires com-
munication and coordination across multiple communities.
While many incidents occur because software design or imple-
mentation deficiencies are exploited, resolution of the
incidents requires more than a technical solution. Communi-
cation of threat and vulnerability information across com-
puting communities is essential to resolving specific
incidents and improving the security of operational systems.
A well formed CERT-System will raise security awareness and
knowledge among site administrators as well as give the
administrators sources of assistance in times of computer
emergencies. By drawing on the experiences of individual
CERT groups, the knowledge level of the CERT-System as a
whole will grow, enabling all members to more effectively
and efficiently deal with computer security incidents as
they arise.
November 14, 1990
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_1. _E_x_a_m_p_l_e _C_E_R_T/_C_C _A_d_v_i_s_o_r_y
CA-90:02
CERT Advisory
March 19, 1990
Internet Intruder Warning
--------------------------------------------------------------------------------------
There have been a number of media reports stemming from a
March 19 New York Times article entitled 'Computer System
Intruder Plucks Passwords and Avoids Detection.' The arti-
cle referred to a program that attempts to get into comput-
ers around the Internet.
At this point, the Computer Emergency Response Team Coordi-
nation Center (CERT/CC) does not have hard evidence that
there is such a program. What we have seen are several per-
sistent attempts on systems using known security vulnerabil-
ities. All of these vulnerabilities have been previously
reported. Some national news agencies have referred to a
'virus' on the Internet; the information we have now indi-
cates that this is NOT true. What we have seen and can con-
firm is an intruder making persistent attempts to get into
Internet systems.
It is possible that a program may be discovered. However,
all the techniques used in these attempts have also been
used, in the past, by intruders probing systems manually.
As of the morning of March 19, we know of several systems
that have been broken into and several dozen more attempts
made on Thursday and Friday, March 15 and 16.
Systems administrators should be aware that many systems
around the Internet may have these vulnerabilities, and
intruders know how to exploit them. To avoid security
breaches in the future, we recommend that all system
administrators check for the kinds of problems noted in this
message.
The rest of this advisory describes problems with system
configurations that we have seen intruders using. In par-
ticular, the intruders attempted to exploit problems in
Berkeley BSD derived UNIX systems and have attacked DEC VMS
systems. In the advisory below, points 1 through 12 deal
with Unix, points 13 and 14 deal with the VMS attacks.
If you have questions about a particular problem, please get
in touch with your vendor.
The CERT makes copies of past advisories available via
anonymous FTP (see the end of this message). Administrators
November 14, 1990
- 9 -
may wish to review these as well.
We've had reports of intruders attempting to exploit the
following areas:
1) Use TFTP (Trivial File Transfer Protocol) to steal pass-
word files.
To test your system for this vulnerability, connect to
your system using TFTP and try 'get /etc/motd'. If you can
do this, anyone else can get your password file as well. To
avoid this problem, disable tftpd.
In conjunction with this, encourage your users to choose
passwords that are difficult to guess (e.g. words that are
not contained in any dictionary of words of any language; no
proper nouns, including names of "famous" real or imaginary
characters; no acronyms that are common to computer profes-
sionals; no simple variations of first or last names, etc.)
Furthermore, inform your users not to leave any clear text
username/password information in files on any system.
If an intruder can get a password file, he/she will usu-
ally take it to another machine and run password guessing
programs on it. These programs involve large dictionary
searches and run quickly even on slow machines. The experi-
ence of many sites is that most systems that do not put any
controls on the types of passwords used probably have at
least one password that can be guessed.
2) Exploit accounts without passwords or known passwords
(accounts with vendor supplied default passwords are favor-
ites). Also uses finger to get account names and then tries
simple passwords.
Scan your password file for extra UID 0 accounts,
accounts with no password, or new entries in the password
file. Always change vendor supplied default passwords when
you install new system software.
3) Exploit holes in sendmail.
Make sure you are running the latest sendmail from your
vendor. BSD 5.61 fixes all known holes that the intruder is
using.
4) Exploit bugs in old versions of FTP; exploit mis-
configured
anonymous FTP
Make sure you are running the most recent version of FTP
which is the Berkeley version 4.163 of Nov. 8 1988. Check
with your vendor for information on configuration upgrades.
Also check your anonymous FTP configuration. It is
November 14, 1990
- 10 -
important to follow the instructions provided with the
operating system to properly configure the files available
through anonymous ftp (e.g., file permissions, ownership,
group, etc.). Note especially that you should not use your
system's standard password file as the password file for
FTP.
5) Exploit the fingerd hole used by the Morris Internet
worm.
Make sure you're running a recent version of finger.
Numerous Berkeley BSD derived versions of UNIX were vulner-
able.
Some other things to check for:
6) Check user's .rhosts files and the /etc/hosts.equiv files
for systems outside your domain. Make sure all hosts in
these files are authorized and that the files are not
world-writable.
7) Examine all the files that are run by cron and at. We've
seen intruders leave back doors in files run from cron or
submitted to at. These techniques can let the intruder back
on the system even after you've kicked him/her off. Also,
verify that all files/programs referenced (directly or
indirectly) by the cron and at jobs, and the job files them-
selves, are not world-writable.
8) If your machine supports uucp, check the L.cmds file to
see if they've added extra commands and that it is owned by
root (not by uucp!) and world-readable. Also, the L.sys
file should not be world-readable or world-writable.
9) Examine the /usr/lib/aliases (mail alias) file for unau-
thorized entries. Some alias files include an alias named
'uudecode'; if this alias exists on your system, and you are
not explicitly using it, then it should be removed.
10) Look for hidden files (files that start with a period
and are normally not shown by ls) with odd names and/or
setuid capabilities, as these can be used to "hide" informa-
tion or privileged (setuid root) programs, including
/bin/sh. Names such as '.. ' (dot dot space space), '...',
and .xx have been used, as have ordinary looking names such
as '.mail'. Places to look include especially /tmp,
/usr/tmp, and hidden directories (frequently within users'
home directories).
11) Check the integrity of critical system programs such as
su, login, and telnet. Use a known, good copy of the pro-
gram, such as the original distribution media and compare it
with the program you are running.
November 14, 1990
- 11 -
12) Older versions of systems often have security vulnera-
bilities that are well known to intruders. One of the best
defenses against problems is to upgrade to the latest ver-
sion of your vendor's system.
VMS SYSTEM ATTACKS:
13) The intruder exploits system default passwords that have
not been changed since installation. Make sure to change
all default passwords when the software is installed. The
intruder also guesses simple user passwords. See point 1
above for suggestions on choosing good passwords.
14) If the intruder gets into a system, often the programs
loginout.exe and show.exe are modified. Check these pro-
grams against the files found in your distribution media.
If you believe that your system has been compromised, con-
tact CERT via telephone or email.
J. Paul Holbrook
Computer Emergency Response Team (CERT)
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890
Internet: cert@cert.sei.cmu.edu
Telephone: 412-268-7090 24-hour hotline: CERT personnel answer
7:30a.m.-6:00p.m. EST, on call for emergencies
other hours.
Past advisories and other information are available for
anonymous ftp from cert.sei.cmu.edu (128.237.253.5).
_R_e_f_e_r_e_n_c_e_s
Dalton90.
Dalton, J., "Building a Constituency - An Ongoing Pro-
cess," _P_r_o_c_e_e_d_i_n_g_s, _C_o_m_p_u_t_e_r _E_m_e_r_g_e_n_c_y _R_e_s_p_o_n_s_e _T_e_a_m
_W_o_r_k_s_h_o_p, 1990.
Danca90.
Danca, R., "Officials Confirm Latest Attempt to Invade
Internet," _F_e_d_e_r_a_l _C_o_m_p_u_t_e_r _W_e_e_k, vol. 4, no. 12, 1990.
Denning90.
Denning, P., _C_o_m_p_u_t_e_r_s _U_n_d_e_r _A_t_t_a_c_k, ACM Press, 1990.
Fedeli90.
Fedeli, A., "Forming and Managing a Response Team,"
_P_r_o_c_e_e_d_i_n_g_s, _C_o_m_p_u_t_e_r _E_m_e_r_g_e_n_c_y _R_e_s_p_o_n_s_e _T_e_a_m _W_o_r_k_s_h_o_p,
1990.
November 14, 1990
- 12 -
Graf90.
Graf, J., "2 Charged With Illegal Computer Use," _C_e_n_t_r_e
_D_a_i_l_y _T_i_m_e_s, February 17, 1990.
Alexander89.
Alexander, M., Johnson, M., "Worm Eats Holes in NASA's
Decnet," _C_o_m_p_u_t_e_r _W_o_r_l_d, October 23, 1989.
Markoff90a.
Markoff, J., "3 Arrests Show Global Threat to Comput-
ers," _N_e_w _Y_o_r_k _T_i_m_e_s, April 4, 1990.
Markoff90b.
Markoff, J., "Student Says His Error Crippled Comput-
ers," _N_e_w _Y_o_r_k _T_i_m_e_s, January 19, 1990.
Quarterman90.
Quarterman, J., _T_h_e _M_a_t_r_i_x: _C_o_m_p_u_t_e_r _N_e_t_w_o_r_k_s _a_n_d _C_o_n_-
_f_e_r_e_n_c_i_n_g _S_y_s_t_e_m_s _W_o_r_l_d_w_i_d_e, Digital Press, 1990.
Scherlis88.
Scherlis, W., "DARPA Establishes Computer Emergency
Response Team," _D_A_R_P_A _P_r_e_s_s _R_e_l_e_a_s_e, December 6, 1988.
Spafford88.
Spafford, E., "The Internet Worm Program: An Analysis,"
Technical Report, Purdue University Department of Com-
puter Sciences, 1988.
Stoll88.
Stoll, C., "Stalking the Wily Hacker," _C_o_m_m_u_n_i_c_a_t_i_o_n_s
_o_f _t_h_e _A_C_M, vol. 31, no. 5, 1988.
Stoll89.
Stoll, C., _T_h_e _C_u_c_k_o_o'_s _E_g_g - _T_r_a_c_k_i_n_g _a _S_p_y _T_h_r_o_u_g_h
_t_h_e _M_a_z_e _o_f _C_o_m_p_u_t_e_r _E_s_p_i_o_n_a_g_e, Doubleday, 1989.
November 14, 1990
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