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Ruby China 的 Mongodb Hash 注入漏洞

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Release： 2016-06-07 16:41:23
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今天在 Ruby China 上看见一个 帖子，从下面的回复中发现是 Mongodb 的漏洞，然后顺便学习了下。 漏洞详细介绍 以用户登陆而言，需要先根据用户传过来的帐户名从数据库中找到这条记录，然后再验证密码。 用户登陆流程 一个登陆表单 input type= "text" name=

今天在 Ruby China 上看见一个 帖子，从下面的回复中发现是 Mongodb 的漏洞，然后顺便学习了下。

漏洞详细介绍

以用户登陆而言，需要先根据用户传过来的帐户名从数据库中找到这条记录，然后再验证密码。

用户登陆流程

一个登陆表单

<span class="nt"><input> <span class="na">type=</span><span class="s">"text"</span> <span class="na">name=</span><span class="s">"session[account]"</span><span class="nt">></span>
<span class="nt"><input> <span class="na">type=</span><span class="s">"text"</span> <span class="na">name=</span><span class="s">"session[password]"</span><span class="nt">></span>
</span></span>
Copy after login

当提交后，服务端得到的数据是这样的（去除其它 token 等信息）。

<span class="p">{</span>
  <span class="s2">"session"</span> <span class="o">=></span> <span class="p">{</span>
    <span class="s2">"account"</span>  <span class="o">=></span> <span class="s2">"username"</span><span class="p">,</span>
    <span class="s2">"password"</span> <span class="o">=></span> <span class="s2">"password"</span>
  <span class="p">}</span>
<span class="p">}</span>
Copy after login

然后服务端通过帐户名从数据库中取得记录

<span class="no">User</span><span class="o">.</span><span class="n">find_by</span><span class="p">(</span><span class="ss">account</span><span class="p">:</span> <span class="n">params</span><span class="o">[</span><span class="ss">:session</span><span class="o">][</span><span class="ss">:account</span><span class="o">]</span><span class="p">)</span>
<span class="c1"># => User.find_by(account: "username")</span>
Copy after login

看起来很正常，但是问题就出现在这一步。

上面的查询语句转换成 Mongodb 查询语句是这样的

<span class="nx">db</span><span class="p">.</span><span class="nx">users</span><span class="p">.</span><span class="nx">find</span><span class="p">({</span> <span class="nx">account</span> <span class="o">:</span> <span class="nx">params</span><span class="p">[</span><span class="o">:</span><span class="nx">session</span><span class="p">][</span><span class="o">:</span><span class="nx">account</span><span class="p">]</span> <span class="p">}).</span><span class="nx">limit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
Copy after login

如果参数是普通的字符串，那么是没有问题的，但是如果它是一个 Hash 呢？

如果 params[:session][:account] 的值是 { "$ne" => "username" }，那么得到的 Mongodb 查询语句就是这样的

<span class="nx">db</span><span class="p">.</span><span class="nx">users</span><span class="p">.</span><span class="nx">find</span><span class="p">({</span> <span class="nx">account</span> <span class="o">:</span> <span class="p">{</span> <span class="nx">$ne</span> <span class="o">:</span> <span class="s2">"username"</span> <span class="p">}</span> <span class="p">}).</span><span class="nx">limit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
Copy after login

这段代码什么意思？找到所有 account 不等于 username 的记录。同样 $ne 可以换成其他 Mongodb 支持的操作，比如 $gt, $lt。username 也可以换成一串乱序字符串，这样就能得到用户集合中的所有记录。

注入

想让服务端得到的参数是 Hash 很简单，只需要手动修改一下表单就行了。

原表单

<span class="nt"><input> <span class="na">type=</span><span class="s">"text"</span> <span class="na">name=</span><span class="s">"session[account]"</span><span class="nt">></span>
</span>
Copy after login

修改后的表单

<span class="nt"><input> <span class="na">type=</span><span class="s">"text"</span> <span class="na">name=</span><span class="s">"session[account][$ne]"</span><span class="nt">></span>
</span>
Copy after login

这样，服务端得到的参数就是这个样子的。

<span class="p">{</span>
  <span class="s2">"session"</span> <span class="o">=></span> <span class="p">{</span>
    <span class="s2">"account"</span>  <span class="o">=></span> <span class="p">{</span>
      <span class="s2">"$ne"</span> <span class="o">=></span> <span class="s2">"username"</span>
    <span class="p">},</span>
    <span class="s2">"password"</span> <span class="o">=></span> <span class="s2">"password"</span>
  <span class="p">}</span>
<span class="p">}</span>
Copy after login
Copy after login

解决方法

将参数转化为字符串

Ruby China 的解决方法就是这种。

<span class="n">account</span> <span class="o">=</span> <span class="n">params</span><span class="o">[</span><span class="ss">:session</span><span class="o">][</span><span class="ss">:account</span><span class="o">].</span><span class="n">to_s</span>
<span class="no">User</span><span class="o">.</span><span class="n">find_by</span><span class="p">(</span><span class="ss">account</span><span class="p">:</span> <span class="n">account</span><span class="p">)</span>
Copy after login

Strong Parameters

Rails 4 开始提供了 Strong Parameters 用来对 params 参数进行过滤。基本语法是

<span class="k">def</span> <span class="nf">session_params</span>
  <span class="n">params</span><span class="o">.</span><span class="n">require</span><span class="p">(</span><span class="ss">:session</span><span class="p">)</span><span class="o">.</span><span class="n">permit</span><span class="p">(</span><span class="ss">:account</span><span class="p">,</span> <span class="ss">:password</span><span class="p">)</span>
<span class="k">end</span>
Copy after login

然后使用过滤后的数据进行查询数据库。

<span class="no">User</span><span class="o">.</span><span class="n">find_by</span><span class="p">(</span><span class="ss">account</span><span class="p">:</span> <span class="n">session_params</span><span class="o">[</span><span class="ss">:account</span><span class="o">]</span><span class="p">)</span>
Copy after login

Strong Parameters

Strong Parameters 是 Rails 4 中提供的用于过滤用户输入的机制，其核心的两个方法是

  • ActionController::Parameters#require
  • ActionController::Parameters#permit

require 用来获取参数中指定键的值

如果不存在则产生 ParameterMissing 异常

对于以下参数

<span class="p">{</span>
  <span class="s2">"session"</span> <span class="o">=></span> <span class="p">{</span>
    <span class="s2">"account"</span>  <span class="o">=></span> <span class="p">{</span>
      <span class="s2">"$ne"</span> <span class="o">=></span> <span class="s2">"username"</span>
    <span class="p">},</span>
    <span class="s2">"password"</span> <span class="o">=></span> <span class="s2">"password"</span>
  <span class="p">}</span>
<span class="p">}</span>
Copy after login
Copy after login

使用 params.require(:session) 后得到的结果是这样的

<span class="p">{</span>
  <span class="s2">"account"</span>  <span class="o">=></span> <span class="p">{</span>
    <span class="s2">"$ne"</span> <span class="o">=></span> <span class="s2">"username"</span>
  <span class="p">},</span>
  <span class="s2">"password"</span> <span class="o">=></span> <span class="s2">"password"</span>
<span class="p">}</span>
Copy after login

permit 用来对参数进行实际的过滤

对于 { "account" => "username", "password" => "password" }，使用 permit(:account, :password) 得到的结果还是原 Hash，因为该 Hash 中的两个键都被 permit 了，而使用 permit(:account) 得到的结果是 { "account" => "username" }，由于没有 permit :password，所以结果中 password 被过滤掉了。

如果是 { "account" => { "$ne" => "username" } } 的话，直接 permit(:account) 的结果是 nil。

如果需要保留多级参数，需要明确指出。

<span class="n">permit</span><span class="p">(</span><span class="ss">:password</span><span class="p">,</span> <span class="ss">account</span><span class="p">:</span> <span class="p">:</span><span class="vg">$ne</span><span class="p">)</span>
<span class="c1"># 或者多个键</span>
<span class="n">permit</span><span class="p">(</span><span class="ss">:password</span><span class="p">,</span> <span class="ss">account</span><span class="p">:</span> <span class="o">[</span> <span class="p">:</span><span class="vg">$ne</span><span class="p">,</span> <span class="p">:</span><span class="vg">$regexp</span> <span class="o">]</span><span class="p">)</span>
Copy after login

总结

  1. 这个漏洞对于普通的用户表单登陆没有多大影响，因为这里只是查找记录，然后验证密码，所以只会提示用户密码错误而已。但是对于 API 接口就有隐患了，API 接口是通过 token 而不是验证密码登陆的。
  2. 这件事让我更加了解了 Rails 4 中 Strong Parameters 的厉害之处！

本文出自：http://blog.sloger.info/, 原文地址：http://sloger.info/posts/mongodb-hash-injection-bugs, 感谢原作者分享。

Related labels：
China hash mongodb ruby injection loopholes
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