PHP Input Validation Vulnerabilities
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| PHP Input Validation Vulnerabilities |
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Date: 12-16-2004
Author: Daniel Fabian
Product: PHP
Vendor: PHP (http://www.php.net)
Vendor-Status: vendor contacted
Vendor-Patches: patched versions have been released
~~~~~~~~
Synopsis
~~~~~~~~~~~~~~~~~~~~~~~~
PHP version 4.3.9 is vulnerable to meta character attacks. The bug could
enable an attacker to read arbitrary files from the filesystem of a
webserver that hosts PHP scripts.
In addition PHP versions 4.3.6 until 4.3.9 as well as PHP versions 5.0.0
until 5.0.2 contain a bug that enables an attacker to manipulate the file
name of uploaded files to perform directory traversal.
While both vulnerabilities exist in windows and unix platform versions of
PHP, they can only be successfully exploited on windows systems.
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Vendor Status
~~~~~~~~~~~~~~~~~~~~~~~~
The vendor has been timely informed and has released patched versions of
the software (PHP 4.3.10/PHP 5.0.3). Those can be downloaded from
http://www.php.net
~~~~~~~~
Vulnerabilities
~~~~~~~~~~~~~~~~~~~~~~~~
addslashes() Vulnerability:
---------------------------
Scope:
PHP version 4.3.9 contains a bug in the function addslashes().
addslashes() can be used to sanitize userinput and render it thus
impossible for an attacker to influence scripts by injection meta
characters. In the default configuration, magic_quotes_gpc is set to "On"
which automagically performs addslashes() on every input value. However
because of a bug, the NULL byte is not correctly encoded by addslashes,
enabling an attacker to read arbitrary files from the file system, if user
input is used within include() or require() directives.
Details:
Addslashes should turn a NULL byte (will be written as %00 in this
advisory) into the string "\0" (backslash zero). In version 4.3.9 the
NULL byte is encoded as "\%00" (backslash null byte). Everything after
the NULL byte is ignored in include and require directives so that an
attacker can truncate the name of the file that is included in the PHP
script. The last character however will always be the backslash. As in
Windows the backslash is the path delimitor, this does not matter - the
file named before the backslash is still loaded.
Example:
Consider the following PHP script:
<?
$whatever = addslashes($_REQUEST['whatever']);
include("/path/to/program/" . $whatever . "/header.htm");
?>
A malicious attacker might open the following URL, disclosing the
boot.ini file:
http://localhost/phpscript.php?whatever=../../../../boot.ini%00
The trailing backslash from the escaped \%00 does for some reason not seem
to be of concern to include().
Upload Path Traversion Vulnerability:
-------------------------------------
Scope:
PHP automatically sanitizes the file name of uploaded files removing
everything before the last slash or backslash. This is done in order to
prevent path traversal attacks with uploaded files. However if an attacker
uploads a file containing a single quote and the attacked web server has
magic_quotes turned on (which is default configuration) or performs an
addslashes() directive on the name of the uploaded file, the quote is
prefixed with a backslash. This occurs after PHP checks for backslashes in
the filename. As the backslash is the path delimitor in windows, this
behavior enables an attacker to traverse the path by one directory level.
Example:
If a file with the name "..'file.ext" is uploaded, PHP turns the name to
"..\'file.ext" and the file is uploaded to the directory below of where
the PHP script copies it.
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Counter Measures
~~~~~~~~~~~~~~~~~~~~~~~~
Upgrade to PHP version 4.3.10, respectively 5.0.3.
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Timeline
~~~~~~~~~~~~~~~~~~~~~~~~
Oct. 08: Notified vendor of addslashes vulnerability
Oct. 14: Vendor reply
Nov. 02: Notified vendor of upload vulnerability
Nov. 04: Vendor reply
Nov. 20: Problems fixed in CVS
Dec. 14: Release of patched versions 4.3.10/5.0.3
EOF Daniel Fabian / @2004
d.fabian at sec-consult dot com
~~~~~~~~
Contact
~~~~~~~~~~~~~~~~~~~~~~~~
SEC Consult Unternehmensberatung GmbH
Büro Wien
Blindengasse 3
A-1080 Wien
Austria
Tel.: +43 / 1 / 409 0307 - 570
Fax.: +43 / 1 / 409 0307 - 590
Mail: office at sec-consult dot com
http://www.sec-consult.com