最近，我们对我们的代码进行了一次安全审计，其中一个问题是我们的应用程序受到Xml外部实体（XXE）攻击。
基本上，应用程序是一个计算器，通过Web服务XML接收输入。
以下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（
我需要做什么来保护我的网络服务？
JAXB
您可以通过从具有IS_SUPPORTING_EXTERNAL_ENTITIES和/或XMLInputFactory的属性设置为XMLStreamReader解组来防止Xml外部实体（XXE）攻击。SUPPORT_DTDfalse。
JAXWS
JAXWS的实现应该为您解决这个问题。如果没有，我建议针对特定的实现打开一个bug。
示例
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
此XML文档包含一个实体，该实体已设置为获取我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>
输出时XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES属性设置为false
设置此属性后，实体不会解析。
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
<name></name>
</customer>
输出时XMLInputFactory.SUPPORT_DTD属性设置为false
设置此属性时，将引发异常以尝试解析实体。
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
