用JAXB防止XXE攻击

Question

最近，我们对代码进行了安全审计，问题之一是我们的应用程序受到Xml eXternal Entity (XXE)攻击。

基本上，应用程序是通过Web接收XML输入的计算器.

下面是对我们的应用程序进行这种XXE攻击的一个例子：

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Header/>
   <soapenv:Body>
      <foo:calculateStuff>
         <!--Optional:-->
         <xmlInput><![CDATA[<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE currency [  
   <!ENTITY include SYSTEM "file:///d:/" >]>
<calcinput>...</calcinput>
]]></xmlInput>
      </foo:calculateStuff>
   </soapenv:Body>
</soapenv:Envelope>

如您所见，我们可以引用指向外部文件("file:///d:/")的实体。

关于XML本身( <calcinput>...</calcinput>部分)是用JAXB (v2.1)进行解组的。web服务部分基于jaxws-rt (2.1)。

我需要做些什么来保护我的网络服务？

Answer 1

JAXB

您可以通过将eXternal和/或XMLInputFactory.SUPPORT_DTD属性设置为false的XMLStreamReader解压缩来防止Xml IS_SUPPORTING_EXTERNAL_ENTITIES实体(XXE)攻击。

JAX-WS

JAX实现应该为您处理这个问题。如果没有，我建议针对特定的植入打开一个bug。

示例

Demo

package xxe;

import javax.xml.bind.*;
import javax.xml.stream.*;
import javax.xml.transform.stream.StreamSource;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Customer.class);

        XMLInputFactory xif = XMLInputFactory.newFactory();
        xif.setProperty(XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES, false);
        xif.setProperty(XMLInputFactory.SUPPORT_DTD, false);
        XMLStreamReader xsr = xif.createXMLStreamReader(new StreamSource("src/xxe/input.xml"));

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        Customer customer = (Customer) unmarshaller.unmarshal(xsr);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(customer, System.out);
    }

}

input.xml

此XML文档包含一个实体，该实体已被设置以获取用于创建此示例的文件列表。

<?xml version="1.0"?>
<!DOCTYPE customer
[
<!ENTITY name SYSTEM "/Users/bdoughan/Examples/src/xxe/">
]
>
<customer>
  <name>&name;</name>
</customer>

客户

package xxe;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Customer {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

输出-默认配置

默认情况下，实体将被解析。

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
    <name>Customer.java
Demo.java
input.xml
</name>
</customer>

将XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES false属性设置为属性时的输出

设置此属性时，该实体不会被解析。

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
    <name></name>
</customer>

将XMLInputFactory.SUPPORT_DTD false属性设置为属性时的输出

设置此属性时，将引发试图解析实体的异常。

Exception in thread "main" javax.xml.bind.UnmarshalException
 - with linked exception:
[javax.xml.stream.XMLStreamException: ParseError at [row,col]:[8,15]
Message: The entity "name" was referenced, but not declared.]
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.handleStreamException(UnmarshallerImpl.java:436)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:372)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.java:342)
    at xxe.Demo.main(Demo.java:18)
Caused by: javax.xml.stream.XMLStreamException: ParseError at [row,col]:[8,15]
Message: The entity "name" was referenced, but not declared.
    at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:598)
    at com.sun.xml.bind.v2.runtime.unmarshaller.StAXStreamConnector.bridge(StAXStreamConnector.java:196)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:370)
    ... 2 more