[UNIX] PHP fopen() Warning Cross-Site Scripting Vulnerability

From: support@securiteam.com
Date: 07/18/02 

From: support@securiteam.com
To: list@securiteam.com
Date: Thu, 18 Jul 2002 07:31:53 +0200 (CEST)

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  PHP fopen() Warning Cross-Site Scripting Vulnerability
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SUMMARY

PHP's fopen() function warning output has been found to inadequately
filter out malicious content, this makes it prone to an XSS security
vulnerability.

DETAILS

Systems Affected:
Any PHP interpreter configured to use error output, and to recognize
warnings as errors; system must host a script-allowing user to open
arbitrary file.

Technical Description:
PHP's default configuration is to display error output in the browser. It
is also configured by default to print out warning messages.

A vulnerability in the way fopen()'s warnings are handled may cause a
cross-site scripting vulnerability.

Demo script:
fo-xss.php:

<?php $handle = fopen($xssvar); ?>

If your system is running a default PHP configuration, this script will
return $xssvar unchanged to the user.

NOTE: This sample requires register_globals to be on.

ADDITIONAL INFORMATION

The information has been provided by <mailto:mattmurphy@kc.rr.com>
Matthew Murphy.

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