------------------------------------------------------------------------- | PHP Input Validation Vulnerabilities | ------------------------------------------------------------------------- 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. ~~~~~~~~ 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. ~~~~~~~~ Counter Measures ~~~~~~~~~~~~~~~~~~~~~~~~ Upgrade to PHP version 4.3.10, respectively 5.0.3. ~~~~~~~~ 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
