=============================================================================
CERT* Advisory CA-97.24
Original issue date: Nov. 05, 1997
Last revised: ---
Topic: Buffer Overrun Vulnerability in Count.cgi cgi-bin Program
- -----------------------------------------------------------------------------
The text of this advisory was originally released on October 31, 1997, as
AA-97.27, developed by the Australian Computer Emergency Response Team. To
more widely broadcast this information, we are reprinting the AUSCERT
advisory here with their permission. Only the contact information at the
end has changed: AUSCERT contact information has been replaced with CERT/CC
contact information.
We will update this advisory as we receive additional information.
Look for it in an "Updates" section at the end of the advisory.
=============================================================================
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.
- - ---------------------------------------------------------------------------
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.
- - ---------------------------------------------------------------------------
AUSCERT thanks Muhammad Muquit for his assistance in the preparation of
this advisory.
- - ---------------------------------------------------------------------------
If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident Response
and Security Teams (see http://www.first.org/team-info/)
CERT/CC Contact Information
- ----------------------------
Email cert@cert.org
Phone +1 412-268-7090 (24-hour hotline)
CERT personnel answer 8:30-5:00 p.m. EST(GMT-5) / EDT(GMT-4)
and are on call for emergencies during other hours.
Fax +1 412-268-6989
Postal address
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
USA
Using encryption
We strongly urge you to encrypt sensitive information sent by email. We can
support a shared DES key or PGP. Contact the CERT/CC for more information.
Location of CERT PGP key
ftp://info.cert.org/pub/CERT_PGP.key
Getting security information
CERT publications and other security information are available from
http://www.cert.org/
ftp://info.cert.org/pub/
CERT advisories and bulletins are also posted on the USENET newsgroup
comp.security.announce
To be added to our mailing list for advisories and bulletins, send
email to
cert-advisory-request@cert.org
In the subject line, type
SUBSCRIBE your-email-address
- ---------------------------------------------------------------------------
Copyright 1997 Carnegie Mellon University. Conditions for use, disclaimers,
and sponsorship information can be found in
http://www.cert.org/legal_stuff.html and ftp://ftp.cert.org/pub/legal_stuff .
If you do not have FTP or web access, send mail to cert@cert.org with
"copyright" in the subject line.
*CERT is registered in the U.S. Patent and Trademark Office.
- ---------------------------------------------------------------------------
This file: ftp://info.cert.org/pub/cert_advisories/CA-97.24.Count_cgi
http://www.cert.org
click on "CERT Advisories"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history
-----BEGIN PGP SIGNATURE-----
Version: 2.6.2
iQCVAwUBNGCSv3VP+x0t4w7BAQF50wQAszcp6TXkVUpxH8Srz3/TFxNroPJVWork
rfW1kpFQyeBoMwUO1LevnmJnXeK6O5YEMZKniy9vxq15KOFDLPvRdhMpBFPZSTlC
5UfYbQs8URETtItLUvgmJTvETfILleI2VdnGkT7HwtG1JPYMZLq/4oLzflgRLDUk
4L9wHCeBL5Q=
=DBiR
-----END PGP SIGNATURE-----