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CERT Advisory CA-2002-21 Vulnerability in PHP
From: CERT Advisory <cert-advisory () cert org>
Date: Mon, 22 Jul 2002 19:09:01 -0400 (EDT)
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CERT Advisory CA-2002-21 Vulnerability in PHP
Original release date: July 22, 2002
Last revised: --
A complete revision history can be found at the end of this file.
* Systems running PHP versions 4.2.0 or 4.2.1
A vulnerability has been discovered in PHP. This vulnerability could
be used by a remote attacker to execute arbitrary code or crash PHP
and/or the web server.
PHP is a popular scripting language in widespread use. For more
information about PHP, see
The vulnerability occurs in the portion of PHP code responsible for
handling file uploads, specifically multipart/form-data. By sending a
specially crafted POST request to the web server, an attacker can
corrupt the internal data structures used by PHP. Specifically, an
intruder can cause an improperly initialized memory structure to be
freed. In most cases, an intruder can use this flaw to crash PHP or
the web server. Under some circumstances, an intruder may be able to
take advantage of this flaw to execute arbitrary code with the
privileges of the web server.
You may be aware that freeing memory at inappropriate times in some
implementations of malloc and free does not usually result in the
execution of arbitrary code. However, because PHP utilizes its own
memory management system, the implementation of malloc and free is
irrelevant to this problem.
Stefan Esser of e-matters GmbH has indicated that intruders cannot
execute code on x86 systems. However, we encourage system
administrators to apply patches on x86 systems as well to guard
against denial-of-service attacks and as-yet-unknown attack techniques
that may permit the execution of code on x86 architectures.
This vulnerability was discovered by e-matters GmbH and is described
in detail in their advisory. The PHP Group has also issued an
advisory. A list of vendors contacted by the CERT/CC and their status
regarding this vulnerability is available in VU#929115.
Although this vulnerability only affects PHP 4.2.0 and 4.2.1,
e-matters GmbH has previously identified vulnerabilities in older
versions of PHP. If you are running older versions of PHP, we
encourage you to review
A remote attacker can execute arbitrary code on a vulnerable system.
An attacker may not be able to execute code on x86 architectures due
to the way the stack is structured. However, an attacker can leverage
this vulnerability to crash PHP and/or the web server running on an
Apply a patch from your vendor
Appendix A contains information provided by vendors for this advisory.
As vendors report new information to the CERT/CC, we will update this
section and note the changes in our revision history. If a particular
vendor is not listed below, we have not received their comments.
Please contact your vendor directly.
Upgrade to the latest version of PHP
If a patch is not available from your vendor, upgrade to version
Deny POST requests
Until patches or an update can be applied, you may wish to deny POST
requests. The following workaround is taken from the PHP Security
If the PHP applications on an affected web server do not rely on
HTTP POST input from user agents, it is often possible to deny POST
requests on the web server.
In the Apache web server, for example, this is possible with the
following code included in the main configuration file or a
top-level .htaccess file:
Deny from all
Note that an existing configuration and/or .htaccess file may have
parameters contradicting the example given above.
Disable vulnerable service
Until you can upgrade or apply patches, you may wish to disable PHP.
As a best practice, the CERT/CC recommends disabling all services that
are not explicitly required. Before deciding to disable PHP, carefully
consider your service requirements.
Appendix A. - Vendor Information
This appendix contains information provided by vendors for this
advisory. As vendors report new information to the CERT/CC, we will
update this section and note the changes in our revision history. If a
particular vendor is not listed below, we have not received their
Apple Computer Inc.
Mac OS X and Mac OS X Server are shipping with PHP version
4.1.2 which does not contain the vulnerability described in
Caldera OpenLinux does not provide either vulnerable version
(4.2.0, 4.2.1) of PHP in their products. Therefore, Caldera
products are not vulnerable to this issue.
Compaq Computer Corporation
SOURCE: Compaq Computer Corporation, a wholly-owned subsidiary
of Hewlett-Packard Company and Hewlett-Packard Company HP
Services Software Security Response Team
x-ref: SSRT2300 php post requests
At the time of writing this document, Compaq is currently
investigating the potential impact to Compaq's released
Operating System software products.
As further information becomes available Compaq will provide
notice of the availability of any necessary patches through
standard security bulletin announcements and be available from
your normal HP Services supportchannel.
Cray, Inc. does not supply PHP on any of its systems.
Debian GNU/Linux stable aka 3.0 is not vulnerable.
Debian GNU/Linux testing is not vulnerable.
Debian GNU/Linux unstable is vulnerable.
The problem effects PHP versions 4.2.0 and 4.2.1. Woody ships
an older version of PHP (4.1.2), that doesn't contain the
FreeBSD does not include any version of PHP by default, and so
is not vulnerable; however, the FreeBSD Ports Collection does
contain the PHP4 package. Updates to the PHP4 package are in
progress and a corrected package will be available in the near
Guardian Digital has not shipped PHP 4.2.x in any versions of
EnGarde, therefore we are not believed to be vulnerable at this
SOURCE: Hewlett-Packard Company Security Response Team
At the time of writing this document, Hewlett Packard is
currently investigating the potential impact to HP's released
Operating System software products.
As further information becomes available HP will provide notice
of the availability of any necessary patches through standard
security bulletin announcements and be available from your
normal HP Services support channel.
IBM is not vulnerable to the above vulnerabilities in PHP. We
do supply the PHP packages for AIX through the AIX Toolbox for
Linux Applications. However, these packages are at 4.0.6 and
also incorporate the security patch from 2/27/2002.
Mandrake Linux does not ship with PHP version 4.2.x and as such
is not vulnerable. The Mandrake Linux cooker does currently
contain PHP 4.2.1 and will be updated shortly, but cooker
should not be used in a production environment and no advisory
will be issued.
Microsoft products are not affected by the issues detailed in
No Netapp products are vulnerable to this.
Red Hat Inc.
None of our commercial releases ship with vulnerable versions
of PHP (4.2.0, 4.2.1).
SuSE Linux is not vulnerable to this problem, as we do not ship
The CERT/CC acknowledges e-matters GmbH for discovering and reporting
Author: Ian A. Finlay.
This document is available from:
CERT/CC Contact Information
Email: cert () cert org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
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Carnegie Mellon University
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July 22, 2002: Initial release
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- CERT Advisory CA-2002-21 Vulnerability in PHP CERT Advisory (Jul 23)