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__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
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__________________________________________________________
INFORMATION BULLETIN
Count.cgi Buffer Overrun Vulnerabiliity
October 31, 1997 22:00 GMT Number I-013
______________________________________________________________________________
PROBLEM: A vulnerability exists in the Count.cgi cgi-bin program.
PLATFORM: Any web server running the count.cgi script.
DAMAGE: Remote users may be able to execute arbitrary commands with the
privileges of the httpd process which answers HTTP requests.
This may be used to compromise the http server and under
certain configurations gain privileged access.
SOLUTION: Install current version of Count.cgi, version 2.4, or apply
workaround.
______________________________________________________________________________
VULNERABILITY It is recommended that sites that have the Count.cgi cgi-bin
ASSESSMENT: program installed take the steps outlined in Section 3 as soon
as possible.
______________________________________________________________________________
[ Start AUSCERT Advisory ]
===========================================================================
AA-97.27 AUSCERT Advisory
Buffer Overrun Vulnerability in Count.cgi cgi-bin Program
31 October 1997
Last Revised: --
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The Australian Computer Emergency Response Team (AUSCERT) has received
information that a buffer overrun vulnerability exists in the Count.cgi
cgi-bin program.
A new version of Count.cgi has been released addressing this vulnerability.
AUSCERT recommends that sites that have the Count.cgi cgi-bin program
installed take the steps outlined in Section 3 as soon as possible.
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1. Description
AUSCERT has received information that a vulnerability exists in the
Count.cgi cgi-bin program. The Count.cgi cgi-bin program is used to
record and display the number of times a WWW page has been accessed.
Due to insufficient bounds checking on arguments which are supplied
by users, it is possible to overwrite the internal stack space of the
Count.cgi program while it is executing. By supplying a carefully
designed argument to the Count.cgi program, intruders may be able to
force Count.cgi to execute arbitrary commands with the privileges of
the httpd process.
The Count.cgi program is extremely widely used. Sites are encouraged
to check for its existence and its possible exploitation.
To check whether exploitation of this vulnerability has been attempted
at your site, search for accesses to the Count.cgi program in your
access logs. An example of how to do this is:
# grep -i 'Count.cgi' {WWW_HOME}/logs/access_log
Where, {WWW_HOME} is the base directory for your web server.
If this command returns anything, further investigation is necessary.
Specifically, look for accesses to Count.cgi that contain long strings
of nonsensical characters.
If sites find any evidence showing that they have been probed using
this vulnerability, they are encouraged to report the incident to
AUSCERT or their local incident response team. Reports of all attacks
help AUSCERT gain a better overview of intruder activity within the
constituency.
2. Impact
Remote user may be able to execute arbitrary commands with the privileges
of the httpd process which answers HTTP requests. This may be used
to compromise the http server and under certain configurations gain
privileged access.
3. Workarounds/Solution
AUSCERT recommends that sites upgrade to the current version of
Count.cgi (Section 3.1). For sites that can not immediately install
the current version of Count.cgi, it is recommended that the workaround
described in Section 3.2 be applied.
3.1 Upgrade to the current Count.cgi version
The author of Count.cgi has recently released version 2.4 which
addresses the vulnerability described in this advisory. AUSCERT
recommends that sites upgrade to the latest version as soon as possible.
The current version is available from:
http://www.fccc.edu/users/muquit/Count.html
3.2 Remove execute permissions
To prevent the exploitation of the vulnerability described in this
advisory, AUSCERT recommends that the execute permissions be removed
from Count.cgi immediately. Note that this will have the side effect
of preventing the page hit counter from being incremented and displayed
on web pages using Count.cgi. The remainder of such web pages should
still display.
4. Additional measures
It is important to note that attacks similar to this may succeed
against any CGI program which has not been written with due consideration
for security. Sites using HTTP servers, and in particular CGI
applications, are encouraged to develop an understanding of the security
issues involved.
Sites should consider taking this opportunity to examine their httpd
configuration and web servers. In particular, all CGI programs that
are not required should be removed, and all those remaining should be
examined for possible security vulnerabilities.
It is also important to ensure that all child processes of httpd are
running as a non-privileged user. This is often a configurable option.
See the documentation for your httpd distribution for more details.
Numerous resources relating to WWW security are available. The following
pages may provide a useful starting point. They include links describing
general WWW security, secure httpd setup and secure CGI programming.
The World Wide Web Security FAQ:
http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
NSCA's "Security Concerns on the Web" Page:
http://hoohoo.ncsa.uiuc.edu/security/
The following books contain useful information including sections on
secure programming techniques.
"Web Security Sourcebook", Aviel Rubin, Daniel Geer and Marcus Ranum,
John Wiley & Sons, Inc., 1997.
"Practical Unix & Internet Security", Simson Garfinkel and
Gene Spafford, 2nd edition, O'Reilly and Associates, 1996.
Please note that the URLs and books referenced in this advisory are
not under AUSCERT's control and therefore AUSCERT cannot be responsible
for their availability or content.
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AUSCERT thanks Muhammad Muquit for his assistance in the preparation of
this advisory.
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The AUSCERT team have made every effort to ensure that the information
contained in this document is accurate. However, the decision to use the
information described is the responsibility of each user or organisation.
The appropriateness of this document for an organisation or individual
system should be considered before application in conjunction with local
policies and procedures. AUSCERT takes no responsibility for the
consequences of applying the contents of this document.
If you believe that your system has been compromised, contact AUSCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).
AUSCERT is located at The University of Queensland within the Prentice
Centre. AUSCERT is a full member of the Forum of Incident Response and
Security Teams (FIRST).
AUSCERT maintains an anonymous FTP service which is found on:
ftp://ftp.auscert.org.au/pub/. This archive contains past SERT and AUSCERT
Advisories, and other computer security information.
AUSCERT also maintains a World Wide Web service which is found on:
http://www.auscert.org.au/.
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 4477
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AUSCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for emergencies.
Postal:
Australian Computer Emergency Response Team
Prentice Centre
The University of Queensland
Brisbane
Qld. 4072.
AUSTRALIA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision History
[ End AUSCERT Advisory ]
______________________________________________________________________________
_
CIAC wishes to acknowledge the contributions of AUSCERT for the
information contained in this bulletin.
______________________________________________________________________________
CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.
CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
Voice: +1 510-422-8193
FAX: +1 510-423-8002
STU-III: +1 510-423-2604
E-mail: ciac@llnl.gov
For emergencies and off-hour assistance, DOE, DOE contractor sites,
and the NIH may contact CIAC 24-hours a day. During off hours (5PM -
8AM PST), call the CIAC voice number 510-422-8193 and leave a message,
or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two
Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC
duty person, and the secondary PIN number, 8550074 is for the CIAC
Project Leader.
Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.
World Wide Web: http://ciac.llnl.gov/
Anonymous FTP: ciac.llnl.gov (198.128.39.53)
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+1 (510) 423-3331 (28.8K baud)
CIAC has several self-subscribing mailing lists for electronic
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1. CIAC-BULLETIN for Advisories, highest priority - time critical
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PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
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