BugTraq: PHP Security Advisory - Apache Module bugs

BugTraq: PHP Security Advisory - Apache Module bugs

January 15, 2001

(From the BugTraq mailing list; HTML encoding added.)

Date: Fri, 12 Jan 2001 21:14:10 +0200
From: Zeev Suraski 
Subject: PHP Security Advisory - Apache Module bugs


[1] PHP supports a configuration mechanism that allows users to configure PHP directives on a per-directory basis. Under Apache, this is usually done using .htaccess files. Due to a bug in the Apache module version of PHP, remote 'malicious users' might be able to create a special HTTP request that would cause PHP to serve the next page with the wrong values for these directives. In certain (fairly rare) situations, this could result in a security problem.

[2] PHP supports the ability to be installed, and yet disabled, by setting the configuration option 'engine = off'. Due to a bug in the Apache module version of PHP, if one or more virtual hosts within a single Apache server were configured with engine=off, this value could 'propagate' to other virtual hosts. Because setting this option to 'off' disables execution of PHP scripts, the source code of the scripts could end up being sent to the end clients.


Even though in their worst-case situations these problems could have severe implications, these worst-cases are rare. In order to take advantage of problem #1, the attacker must have good knowledge of the structure of the site, the values of the various PHP directives in each directory, and a way that would help him exploit the bug using this knowledge. In addition, he must also be lucky enough to perform the attack on the same Apache httpd process that he exploits in a prior request, which can be very difficult to do on a busy site.

Problem #2 is more serious, but because of its severity, it's most often detected immediately. This problem also only affects a setup that has multiple virtual hosts with some of them configured not to allow execution of PHP scripts, which is pretty rare.

Affected Software Versions

All versions of PHP 4.0, from PHP 4.0.0 (and possibly earlier betas) through PHP 4.0.4 are vulnerable to these problems. Note that only the Apache module version of PHP is vulnerable - the CGI module as well as other server modules are *NOT* affected.

PHP 3.0 is *NOT* affected.


The recommended solution is to upgrade to PHP 4.0.4pl1, available at http://www.php.net/downloads.php

A workaround for problem #2 is to explicitly set 'engine=on' on all of the virtual hosts that are supposed to serve PHP pages, if one or more virtual hosts is configured with engine=off.

A partial workaround for problem #1 is to disallow 'OPTIONS' requests.


I'd like to thank James Moore, which, after hearing about the bug report, managed to successfully reproduce it, and issue a pin-pointing problem description, that helped solve the bug instantly.


PHP Group

Zeev Suraski 
CTO &  co-founder, Zend Technologies Ltd. http://www.zend.com/