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CERT* Advisory CA-97.24
Original issue date: Nov. 05, 1997
Last revised: November 14, 1997
              UPDATES - Corrected a URL.

              A complete revision history is at the end of this file.

Topic:  Buffer Overrun Vulnerability in Count.cgi cgi-bin Program

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   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.

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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.
- - ---------------------------------------------------------------------------

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

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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.
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This file: ftp://info.cert.org/pub/cert_advisories/CA-97.24.Count_cgi
           http://www.cert.org
               click on "CERT Advisories"

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UPDATES

November 14, 1997
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CERT/CC received word that the URL for NSCA's "Security Concerns on
the Web" in the AUSCERT advisory was not correct and should be changed
to the following URL:

        http://hoohoo.ncsa.uiuc.edu/security-1.0/

Our thanks to Zachary Uram at Carnegie Mellon University for bringing
this to our attention.

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Revision history

Nov. 14, 1997 - UPDATES: Corrected a URL.

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