CERT Advisory CA-2002-21 Vulnerability in PHP

From: CERT Advisory (cert-advisory@cert.org)
Date: 07/23/02

Date: Mon, 22 Jul 2002 19:09:01 -0400 (EDT)
From: CERT Advisory <cert-advisory@cert.org>
To: cert-advisory@cert.org


CERT Advisory CA-2002-21 Vulnerability in PHP

   Original release date: July 22, 2002
   Last revised: --
   Source: CERT/CC

   A complete revision history can be found at the end of this file.

Systems Affected

     * 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.

I. Description

   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

II. Impact

   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
   x86 architecture.

III. Solution

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:

     <Limit POST>
        Order deny,allow
        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
          this alert.


          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.

          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
          vulnerable function.


          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

          Guardian Digital has not shipped PHP 4.2.x in any versions of
          EnGarde, therefore we are not believed to be vulnerable at this

Hewlett-Packard Company

          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 Corporation

          Microsoft products are not affected by the issues detailed in
          this advisory.

Network Appliance

          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 Inc.

          SuSE Linux is not vulnerable to this problem, as we do not ship
          PHP 4.2.x.

   The CERT/CC acknowledges e-matters GmbH for discovering and reporting
   this vulnerability.

   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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   Revision History
July 22, 2002: Initial release

Version: PGP 6.5.8


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