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  • CERT Advisory CA-2002-21 Vulnerability in PHP

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Original release date: July 22, 2002
Last revised: Thu Jul 25 09:23:27 EDT 2002
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 4.2.2.

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 Advisory:

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 comments.

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

We have verified that this problem is not present on our distributions for HP Tru64 UNIX or HP OpenVMS products.


PHP 4.2.x is not shipped with Conectiva Linux.

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.

F5 Networks, Inc.

F5 Networks products do not include PHP 4.2.0 or 4.2.1, and are therefore not affected by this vulnerability.


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 future.

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 time.

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).


SGI acknowledges the PHP vulnerabilitity reported by CERT and is currently investigating. PHP does not currently ship as part of IRIX so SGI can confirm that base IRIX is not vulnerable. No further information is available at this time.

For the protection of all our customers, SGI does not disclose, discuss or confirm vulnerabilities until a full investigation has occurred and any necessary patch(es) or release streams are available for all vulnerable and supported IRIX operating systems. Until SGI has more definitive information to provide, customers are encouraged to assume all security vulnerabilities as exploitable and take appropriate steps according to local site security policies and requirements. As further information becomes available, additional advisories will be issued via the normal SGI security information distribution methods including the wiretap mailing list on

SuSE Inc.

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


The TSL team states that none of the versions of the Trustix Secure Linux distribution is vulnerable to the php 4.2.{0,1} vulnerability (CA-2002-21) as none of the TSL versions is shipped with php 4.2.x.

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

Author: Ian A. Finlay.

Copyright 2002 Carnegie Mellon University.

Revision History

July 22, 2002: Initial release
July 23, 2002: Added vendor statement for F5 Networks, Inc.
July 23, 2002: Added vendor statement for Conectiva
July 24, 2002: Added vendor statement for Trustix
July 24, 2002: Added vendor statement for SGI
July 25, 2002: Updated vendor statement for Compaq Computer Corporation

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