Security Advisory: Vulnerability in PHP versions 4.2.0 and 4.2.1

PHP Security Advisory: Vulnerability in PHP versions 4.2.0 and 4.2.1

Issued on: July 22, 2002
Software: PHP versions 4.2.0 and 4.2.1
Platforms: All

The PHP Group has learned of a serious security vulnerability in PHP
versions 4.2.0 and 4.2.1. An intruder may be able to execute arbitrary
code with the privileges of the web server. This vulnerability may be
exploited to compromise the web server and, under certain conditions,
to gain privileged access.

Description

PHP contains code for intelligently parsing the headers of HTTP POST
requests. The code is used to differentiate between variables and files
sent by the user agent in a "multipart/form-data" request. This parser
has insufficient input checking, leading to the vulnerability.

The vulnerability is exploitable by anyone who can send HTTP POST
requests to an affected web server. Both local and remote users, even
from behind firewalls, may be able to gain privileged access.

Impact

Both local and remote users may exploit this vulnerability to compromise
the web server and, under certain conditions, to gain privileged access.
So far only the IA32 platform has been verified to be safe from the
execution of arbitrary code. The vulnerability can still be used on IA32
to crash PHP and, in most cases, the web server.

Solution

The PHP Group has released a new PHP version, 4.2.2, which incorporates
a fix for the vulnerability. All users of affected PHP versions are
encouraged to upgrade to this latest version. The downloads web site at

  http://www.php.net/downloads.php

has the new 4.2.2 source tarballs, Windows binaries and source patches
from 4.2.0 and 4.2.1 available for download.

Workaround

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.

Credits

The PHP Group would like to thank Stefan Esser of e-matters GmbH for
discovering this vulnerability.

Copyright (c) 2002 The PHP Group.