Advisory EM01/2002: Multiple Remote Vulnerabilites within PHP's fileupload code



                           e-matters GmbH
www.e-matters.de

-= Security Advisory =-



Advisory: Multiple Remote Vulnerabilites within PHP's fileupload code
Release Date: 2002/02/27
Last Modified: 2002/02/28
Author: Stefan Esser [s.esser@hardened-php.net]

Application: PHP v3.0.10-v3.0.18, v4.0.1-v4.1.1
Severity: Several vulnerabilities in PHP's fileupload code allow
remote compromise
Risk: Critical
Vendor Status: Patches Released
Reference: http://security.e-matters.de/advisories/012002.html



Overview:

We found several flaws in the way PHP handles multipart/form-data POST
requests. Each of the flaws could allow an attacker to execute arbitrary
code on the victim's system.


Details:

PHP supports multipart/form-data POST requests (as described in RFC1867)
known as POST fileuploads. Unfourtunately there are several flaws in the
php_mime_split function that could be used by an attacker to execute
arbitrary code. During our research we found out that not only PHP4 but
also older versions from the PHP3 tree are vulnerable.


The following is a list of bugs we found:

PHP 3.0.10-3.0.18

- broken boundary check (hard to exploit)
- arbitrary heap overflow (easy exploitable)

PHP 4.0.1-4.0.3pl1

- broken boundary check (hard to exploit)
- heap off by one (easy exploitable)

PHP 4.0.2-4.0.5

- 2 broken boundary checks (one very easy and one hard to exploit)

PHP 4.0.6-4.0.7RC2

- broken boundary check (very easy to exploit)

PHP 4.0.7RC3-4.1.1

- broken boundary check (hard to exploit)


Finally I want to mention that the boundary check vulnerabilities
are only exploitable on linux or solaris.
The heap off by one is only exploitable on linux(maybe solaris)x86
and the arbitrary heap overflow in PHP3 is exploitable on most OS
and architectures. (This includes *BSD, Windows, Linux, Solaris)

Users running PHP 4.2.0-dev from cvs are not vulnerable to any of the
described bugs because the fileupload code was completly rewritten for
the 4.2.0 branch.

Please notice, that you are not only vulnerable if you run scripts
that use uploaded files. You are vulnerable if you run any script!
If you have PHP only installed but there is no script on your
server you are not vulnerable.

Please notice also, that the PHP team now learned that there is
really a badly working exploit circulating in the underground.
At the time this advisory was originaly posted we only heard
rumours.


Proof of Concept:

e-matters is not going to release exploits for any of the discovered
vulnerabilities to the public.


Vendor Response:

Because I am part of the php developer team there is not much I can
write here...

27th February 2002 - An updated version of php and the patch for
these vulnerabilities are now available at:
http://www.php.net/downloads.php


Recommendation:

If you are running PHP 4.0.3 or above one way to workaround these
bugs is to disable the fileupload support within your php.ini
(file_uploads = Off) If you are running php as module keep in mind
to restart the webserver. Anyway you should better install the
fixed or a properly patched version to be safe.


Sidenotice:

This advisory is so short because I don't want to give out more info
than is needed.

Users running the developer version of php (4.2.0-dev) are not
vulnerable to these bugs because the fileupload support was completly
rewritten for that branch.


GPG-Key:

http://security.e-matters.de/gpg_key.asc

pub 1024D/75E7AAD6 2002-02-26 e-matters GmbH - Securityteam
Key fingerprint = 43DD 843C FAB9 832A E5AB CAEB 81F2 8110 75E7 AAD6


Copyright 2002 Stefan Esser. All rights reserved.


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