如何在.net反序列化期间防止XML外部实体(XXE)攻击

Question

我们正在使用veracode对代码进行安全性分析,并在下面的代码中显示XXE缺陷,特别是在调用Deserialize()的情况下.我们如何防止序列化程序访问外部实体.我在下面尝试将XMLresolver的XMLresolver设置为null无法正常工作.

    public static T DeserializeObject(string xml, string Namespace)
    {
        System.Xml.Serialization.XmlSerializer serializer = new System.Xml.Serialization.XmlSerializer(typeof(T), Namespace);

        MemoryStream stream =
                new MemoryStream(Encoding.Default.GetBytes(xml));
        XmlReaderSettings settings = new XmlReaderSettings();

        // allow entity parsing but do so more safely
        settings.DtdProcessing = DtdProcessing.Ignore;
        settings.XmlResolver = null;

        using (XmlReader reader = XmlReader.Create(stream, settings))
        {
            return serializer.Deserialize(reader) as T;
        }
    }

任何人都可以建议我可能会缺少什么或者是否还有其他事情要尝试.

Answer 1

我有类似的问题。当您从字符串中读取时，需要将 xmlReader 更改为 xmlTextReader。

像这样的东西-

  public static T DeserializeObject(string xml, string Namespace)
  {
        System.Xml.Serialization.XmlSerializer serializer = new System.Xml.Serialization.XmlSerializer(typeof(T), Namespace);

        //**** I don't think you need this block of code *********
        //MemoryStream stream = new MemoryStream(Encoding.Default.GetBytes(xml));
        //XmlReaderSettings settings = new XmlReaderSettings();

        // allow entity parsing but do so more safely
        //settings.DtdProcessing = DtdProcessing.Ignore;
        //settings.XmlResolver = null;
        //*********************************************

        XmlTextReader reader = new XmlTextReader(xml)
        {
            XmlResolver = null
        };

        return serializer.Deserialize(reader) as T;
  }

一切顺利！