使用JAXB防止XXE攻击

Question

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

基本上，该应用程序是一个计算器，可通过Web服务以XML形式接收输入。

这是对我们的应用程序进行此类XXE攻击的示例：

<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输入本身（该<calcinput>...</calcinput>部分）未与JAXB（v2.1）一起编组。Web服务部分基于jaxws-
rt（2.1）。

我需要做什么来保护我的Web服务？

Answer 1

杰克斯

您可以通过XMLStreamReader将IS_SUPPORTING_EXTERNAL_ENTITIES和和/或XMLInputFactory.SUPPORT_DTD属性设置为的取消编组，以防止Xml
eXternal Entity（XXE）攻击false。

JAX-WS

JAX-WS实现应为您解决这一问题。如果没有，我建议针对特定的实现打开一个错误。

例

演示版

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

该XML文档包含一个实体，该实体已设置为获取我用来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>

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，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>

XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES 属性设置为时输出false

设置此属性后，不会解析该实体。

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

XMLInputFactory.SUPPORT_DTD 属性设置为时输出false

设置此属性后，将尝试抛出异常来解析该实体。

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