防止XXE攻击与JAXB(Prevent XXE Attack with JAXB)

最近，我们对我们的代码安全审计，问题之一就是我们的应用程序受到的XML外部实体 （XXE）攻击。

基本上，应用是接收输入作为XML，通过web服务的计算器。

这里是我们的应用程序这样的XXE攻击的例子：

<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>

正如你所看到的，我们可以参考指向外部文件的实体（ "file:///d:/" ）。

关于XML输入本身（ <calcinput>...</calcinput>部分）解组与JAXB（V2.1）。 web服务部分是基于JAXWS-RT（2.1）。

我需要做什么做，以确保我的Web服务？

JAXB

您可以通过从解组阻止的xml外部实体（XXE）攻击XMLStreamReader具有IS_SUPPORTING_EXTERNAL_ENTITIES和/或XMLInputFactory.SUPPORT_DTD设置为性能false 。

JAX-WS

JAX-WS实现应该照顾这对你。如果没有，我会建议开一个bug具体对阵implmententation。

例

演示

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中

这个XML文档包含已设置让我用来创建这个例子中的文件列表的实体。

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

顾客

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，该实体将得到解决。

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

当输出XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES属性设置为false

当这个属性被设置实体没有得到解决。

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

当输出XMLInputFactory.SUPPORT_DTD属性设置为false

当此属性设置一个异常被抛出试图解决实体。

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