M-049: Multiple PHP Vulnerabilities

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Internet Security Systems Security Alert
February 27, 2002 

Multiple PHP Vulnerabilities: Remote Compromise Exploit in Circulation 

Synopsis: 

ISS X-Force has learned of multiple buffer overflow vulnerabilities present in the PHP 
(Hypertext Preprocessor) scripting language. PHP is a popular server-side scripting 
language that is used heavily throughout the Internet. PHP is most commonly used in 
Apache Web server environments, but it is supported by all major Web servers and 
operating systems. X-Force has verified that a functional exploit for one of the 
vulnerabilities exists and may be actively circulating in the computer underground. 

Impact: 

Netcraft reports that as of January 2002, there are over 20.8 million active Apache 
installations, which account for 57% of the sites surveyed. Secure Space reports that 
PHP is the most popular Apache module available and there are over 1.44 million active 
installations. 

Affected Platforms: 

PHP version 3.0.10-3.0.18
PHP version 4.0.1-4.03pl1
PHP version 4.0.2-4.05
PHP version 4.0.6-4.0.7RC2
PHP version 4.0.7RC3-4.1.1

The PHP 4.2.0-dev distribution is not vulnerable.


Description: 

The PHP project began as an Apache Software Foundation project as a powerful, cross-
platform, server-side, embedded scripting language. PHP code is included inline among 
common HTML scripting, and its commands are executed on the server, unlike JavaScript, 
which is executed on the client. PHP is an attractive alternative for Web developers 
who are interested in creating dynamic content because it is considered easy to work 
with, very fast, and extremely flexible. 

PHP supports file uploads via HTTP POST by any RFC-1867 compliant Web browser. This 
feature allows Web site visitors to upload files, scripting, or any type of content to 
the server, where it can then be stored, displayed, or operated upon, depending on the 
design of the server. This feature is considered a potential security risk and many 
security mechanisms have been added to PHP over time to limit its abuse. 

Multiple buffer overflow vulnerabilities exist within the HTTP POST file upload 
functionality. To successfully exploit these vulnerabilities, attackers must upload a 
PHP form containing specially crafted MIME encoded data. In the exploit X-Force has 
analyzed, this data is passed in a buffer to a routine that locates the MIME boundary. 
A pointer is set to point to the end of the boundary, and then the "Content- 
disposition" header is parsed. A logic flaw in the parsing routine may cause PHP to 
miscalculate the remaining byte count within the allocated buffer. Under certain 
circumstances, this may lead to a one-byte overflow within the heap memory management 
data. 

Heap overflows are inherently difficult to exploit because the nature of the memory 
heap is much more dynamic then that of the stack. The environment of the heap 
management system must be favorable to the attacker to successfully exploit this 
vulnerability. Web servers are constantly allocating more memory dynamically and are 
serving many clients at any given time. This environment is quite chaotic and 
decreases the chances of successful exploitation in real-world conditions. 

X-Force has analyzed and tested a functional exploit. This exploit is believed to be 
circulating in the underground community and in use to a limited degree. It contains 
nine separate exploit vectors for versions of Debian and Red Hat Linux running various 
versions of Apache Web server and PHP. X-Force predicts newer versions of this exploit 
may support exploit vectors covering additional operating systems. 

Recommendations: 

The exploit that X-Force has analyzed appears to be an early version, and is somewhat 
unreliable. X-Force has been able to compromise remote servers with this current 
exploit in a lab environment. Newer and more effective versions may be circulating as 
well. 

The maintainers of PHP have updated the PHP CVS source code repository to fix this 
vulnerability. X-Force recommends that Web site administrators upgrade to the latest 
versions available for their PHP distributions. PHP downloads are available at:
http://www.php.net/downloads.php 

The vulnerability associated with the exploit has been fixed in the file 
"php4/main/rfc1867.c". PHP4 administrators should verify that the revision of this 
file is 1.71.2.1 or higher. The latest PHP version 4.1.2 packages contain the patched 
version of "rfc1867.c". 

As a workaround, the file upload support can be disabled on Web servers running PHP 
4.0.3 or above. Open the php.ini file and modify the line file_uploads = On to 
file_uploads = Off. After modifying the php.ini file, the Web server must be restarted 
if PHP is running as module. 

An X-Press Update for RealSecure Network Sensor will be available soon to provide 
detection support for these vulnerabilities. An Internet Scanner Flex Check will be 
released today to find vulnerable versions of PHP. These updates will be available at 
the ISS Download Center at:
http://www.iss.net/download 

Additional Information: 

Advisory: PHP remote vulnerabilities,
http://security.e-matters.de/advisories/012002.html 

PHP Downloads,
http://www.php.net/downloads.php 

Apache Module Report,
http://www.securityspace.com/s_survey/data/man.200201/apachemods.html 

Netcraft,
http://www.netcraft.com 

ISS X-Force Database,
http://www.iss.net/security_center/static/8281.php 

ISS Download Center,
http://www.iss.net/download 

This alert is available at:
http://www.iss.net/security_center/alerts/advise112.php 

Credits: 

ISS would like to thank Snort for providing the exploit for this vulnerability. 

______ 

About Internet Security Systems (ISS)
Founded in 1994, Internet Security Systems (ISS) (Nasdaq: ISSX) is a pioneer and world 
leader in software and services that protect critical online resources from an ever-
changing spectrum of threats and misuse. Internet Security Systems is headquartered in 
Atlanta, GA, with additional operations throughout the Americas, Asia, Australia, 
Europe and the Middle East. 

Copyright (c) 2002 Internet Security Systems, Inc. All rights reserved worldwide. 

Permission is hereby granted for the electronic redistribution of this document. It is 
not to be edited or altered in any way without the express written consent of the 
Internet Security Systems X-Force. If you wish to reprint the whole or any part of 
this document in any other medium excluding electronic media, please email 
xforce@iss.net for permission. 

Disclaimer: The information within this paper may change without notice. Use of this 
information constitutes acceptance for use in an AS IS condition. There are NO 
warranties, implied or otherwise, with regard to this information or its use. Any use 
of this information is at the user's risk. In no event shall the author/distributor 
(Internet Security Systems X-Force) be held liable for any damages whatsoever arising 
out of or in connection with the use or spread of this information. 

X-Force PGP Key available on MIT's PGP key server and PGP.com's key server, as well as 
at http://www.iss.net/security_center/sensitive.php 

Please send suggestions, updates, and comments to: X-Force xforce@iss.net of Internet 
Security Systems, Inc. 


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