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iDEFENSE Security Advisory 10.03.2002
Apache 1.3.x shared memory scoreboard vulnerabilities

16:00 GMT, October 3, 2002

I. BACKGROUND

The Apache Software Foundation's HTTP Server is an effort to develop
and maintain an open-source HTTP server for modern operating systems
including Unix and Windows NT. The goal of this project is to provide
a secure, efficient and extensible server that provides HTTP services
in sync with the current HTTP standards. More details about it are
available at http://httpd.apache.org .

II. DESCRIPTION

Apache HTTP Server contains a vulnerability in its shared memory
scoreboard. Attackers who can execute commands under the Apache UID
can either send a (SIGUSR1) signal to any process as root, in most
cases killing the process, or launch a local denial of service (DoS)
attack.

III. ANALYSIS

Exploitation requires execute permission under the Apache UID. This
can be obtained by any local user with a legitimate Apache scripting
resource (ie: PHP, Perl), exploiting a vulnerability in web-based
applications written in the above example languages, or through the
use of some other local/remote Apache exploit.

Once such a status is attained, the attacker can then attach to the
httpd daemon's 'scoreboard', which is stored in a shared memory
segment owned by Apache. The attacker can then cause a DoS condition
on the system by continuously filling the table with null values and
causing the server to spawn new children.

The attacker also has the ability to send any process a SIGUSR1
signal as root. This is accomplished by continuously overwriting the
parent[].pid and parent[].last_rtime segments within the scoreboard
to the pid of the target process and a time in the past. When the
target pid receives the signal SIGUSR1, it will react according to
how it is designed to manage the signal. According to the man page
(man 7 signal), if the signal is un-handled then the default action
is to terminate:

     ...
     SIGUSR1 30,10,16 A User-defined signal 1
     ...
     The letters in the "Action" column have the following meanings:

     A Default action is to terminate the process.
     ...

iDEFENSE successfully terminated arbitrary processes, including those
that "kicked" people off the system.

IV. DETECTION

Apache HTTP Server 1.3.x, running on all applicable Unix platforms,
is affected.

V. VENDOR FIX/RESPONSE

Apache HTTP Server 1.3.27 fixes this problem. It should be available
on October 3 at http://www.apache.org/dist/httpd/ .

VI. CVE INFORMATION

The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project
has assigned the identification number CAN-2002-0839 to this issue.

VII. DISCLOSURE TIMELINE

8/27/2002 Issue disclosed to iDEFENSE
9/18/2002 Vendor notified at securityapache.org
9/18/2002 iDEFENSE clients notified
9/19/2002 Response received from Mark J Cox (markawe.com)
10/3/2002 Coordinated public disclosure

VIII. CREDIT

zen-parse (zen-parsegmx.net) disclosed this issue to iDEFENSE.

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About iDEFENSE:

iDEFENSE is a global security intelligence company that proactively
monitors sources throughout the world — from technical
vulnerabilities and hacker profiling to the global spread of viruses
and other malicious code. iALERT, our security intelligence service,
provides decision-makers, frontline security professionals and
network administrators with timely access to actionable intelligence
and decision support on cyber-related threats. For more information,
visit http://www.idefense.com.

- -dave

David Endler, CISSP
Director, Technical Intelligence
iDEFENSE, Inc.
14151 Newbrook Drive
Suite 100
Chantilly, VA 20151
voice: 703-344-2632
fax: 703-961-1071

dendleridefense.com
www.idefense.com

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