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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
Overview
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
http://www.php.net/manual/en/faq.general.php
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
http://security.e-matters.de/advisories/012002.html
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
</Limit>
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
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
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
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
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.
Mandrakesoft
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:
http://www.cert.org/advisories/CA-2002-21.html
______________________________________________________________________
CERT/CC Contact Information
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Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
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Revision History
July 22, 2002:  Initial release
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