【JAVA XXE攻击】微信支付官方回应XML外部实体注入漏洞

官方回应连接：https://pay.weixin.qq.com/wiki/doc/api/jsapi.php?chapter=23_5

其中明确指出了代码修改的地方。

然后看到此文档后，我就改公司项目中代码，项目中支付时并没有涉及到XML解析，

而是在支付后，微信回调告知支付结果时，我这边接受时需要解析XML。

    /**
     * 解析xml,返回第一级元素键值对。如果第一级元素有子节点，则此节点的值是子节点的xml数据。
     * @param strxml
     * @return
     * @throws JDOMException
     * @throws IOException
     */
    public static Map doXMLParse(String strxml) throws JDOMException, IOException {
        if(null == strxml || "".equals(strxml)) {
            return null;
        }

        Map m = new HashMap();
        InputStream in = HttpClientUtil.String2Inputstream(strxml);
        SAXBuilder builder = new SAXBuilder();

        Document doc = builder.build(in);
        Element root = doc.getRootElement();

        List list = root.getChildren();
        Iterator it = list.iterator();
        while(it.hasNext()) {
            Element e = (Element) it.next();
            String k = e.getName();
            String v = "";
            List children = e.getChildren();
            if(children.isEmpty()) {
                v = e.getTextNormalize();
            } else {
                v = XMLUtil.getChildrenText(children);
            }

            m.put(k, v);
        }

很明显，我这个原有的代码中解析XML时，并没有“DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();”，而是 SAXBuilder builder = new SAXBuilder();

后来发现当使用SAXBuilder时 ，可以这样处理以达到防止XXE攻击。

/**
     * 解析xml,返回第一级元素键值对。如果第一级元素有子节点，则此节点的值是子节点的xml数据。
     * @param strxml
     * @return
     * @throws JDOMException
     * @throws IOException
     */
    public static Map doXMLParse(String strxml) throws JDOMException, IOException {
        if(null == strxml || "".equals(strxml)) {
            return null;
        }

        Map m = new HashMap();
        InputStream in = HttpClientUtil.String2Inputstream(strxml);
        SAXBuilder builder = new SAXBuilder();

        // 这是优先选择. 如果不允许DTDs (doctypes) ,几乎可以阻止所有的XML实体攻击
        String FEATURE = "http://apache.org/xml/features/disallow-doctype-decl";
        builder.setFeature(FEATURE, true);

        FEATURE = "http://xml.org/sax/features/external-general-entities";
        builder.setFeature(FEATURE, false);

        FEATURE = "http://xml.org/sax/features/external-parameter-entities";
        builder.setFeature(FEATURE, false);

        FEATURE = "http://apache.org/xml/features/nonvalidating/load-external-dtd";
        builder.setFeature(FEATURE, false);

        Document doc = builder.build(in);
        Element root = doc.getRootElement();

        List list = root.getChildren();
        Iterator it = list.iterator();
        while(it.hasNext()) {
            Element e = (Element) it.next();
            String k = e.getName();
            String v = "";
            List children = e.getChildren();
            if(children.isEmpty()) {
                v = e.getTextNormalize();
            } else {
                v = XMLUtil.getChildrenText(children);
            }

            m.put(k, v);
        }

        //关闭流
        in.close();

        return m;
    }

即：设置builder的feature ，

/ 这是优先选择. 如果不允许DTDs (doctypes) ,几乎可以阻止所有的XML实体攻击
        String FEATURE = "http://apache.org/xml/features/disallow-doctype-decl";
        builder.setFeature(FEATURE, true);

        FEATURE = "http://xml.org/sax/features/external-general-entities";
        builder.setFeature(FEATURE, false);

        FEATURE = "http://xml.org/sax/features/external-parameter-entities";
        builder.setFeature(FEATURE, false);

        FEATURE = "http://apache.org/xml/features/nonvalidating/load-external-dtd";
        builder.setFeature(FEATURE, false);