Original issue date: November 5, 1997<BR>
Last revised: November 14, 1997<BR>
UPDATES - Corrected a URL.
<P>A complete revision history is at the end of this file.
<P>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.
<P>We will update this advisory as we receive additional information. Look
for it in an "Updates" section at the end of the advisory.
<P><HR>
<P>The Australian Computer Emergency Response Team (AUSCERT) has received
information that a buffer overrun vulnerability exists in the Count.cgi
cgi-bin program.
<P>A new version of Count.cgi has been released addressing this vulnerability.
<P>AUSCERT recommends that sites that have the Count.cgi cgi-bin program
installed take the steps outlined in Section 3 as soon as possible.
<P><HR>
<H2>I. Description</H2>
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.
<P>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.
<P>The Count.cgi program is extremely widely used. Sites are encouraged
to check for its existence and its possible exploitation.
<P>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:
<PRE> # grep -i 'Count.cgi' {WWW_HOME}/logs/access_log</PRE>
Where {WWW_HOME} is the base directory for your web server.
<P>If this command returns anything, further investigation is necessary.
Specifically, look for accesses to Count.cgi that contain long strings
of nonsensical characters.
<P>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.
<H2>II. Impact</H2>
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.
<H2>III. Workarounds/Solution</H2>
AUSCERT recommends that sites upgrade to the current version of Count.cgi
(Section III.A). 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.
<H3>A. Upgrade to the current Count.cgi version</H3>
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:
<P><A HREF="http://www.fccc.edu/users/muquit/Count.html">http://www.fccc.edu/users/muquit/Count.html</A>
<H3>B. Remove execute permissions</H3>
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.
<H2>IV. Additional measures</H2>
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.
<P>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.
<P>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.
<P>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.
<P>The World Wide Web Security FAQ:
<BR><A HREF="http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html">http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html</A>
<P>NSCA's "Security Concerns on the Web" Page:
<BR><A HREF="http://hoohoo.ncsa.uiuc.edu/security/">http://hoohoo.ncsa.uiuc.edu/security/</A>
<P>The following books contain useful information including sections on
secure programming techniques.
<P><I>Web Security Sourcebook</I>, Aviel Rubin, Daniel Geer and Marcus Ranum,
John Wiley & Sons, Inc., 1997.
<P><I>Practical Unix & Internet Security</I>, Simson Garfinkel and Gene
Spafford, 2nd edition, O'Reilly and Associates, 1996.
<P>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.
<P><HR>
<P>AUSCERT thanks Muhammad Muquit for his assistance in the preparation
of this advisory.
<P>
<HR>
<H2>UPDATES</H2>
<H3>November 14, 1997</H3>
<P>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:
<P>
<P><A HREF="http://hoohoo.ncsa.uiuc.edu/security-1.0/">http://hoohoo.ncsa.uiuc.edu/security-1.0/</A>
<HR>
<P>Our thanks to Zachary Uram at Carnegie Mellon University for bringing
this to our attention.
<P><HR>
<P><HR>
<!--#include virtual="/include/footer_nocopyright.html" -->
<P>Copyright 1997 Carnegie Mellon University.</P>
<HR>
Revision History
<PRE>
Nov. 14, 1997 UPDATES - Corrected a URL.
</PRE> |