如何防止 XML 注入如 XML Bomb 和 XXE 攻击

Question

我正在开发一个 android 应用程序

android:minSdkVersion="14"

在这个应用程序中需要解析一个 xml。为此，我正在使用这样的 DOM 解析器

DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = null;
Document doc = null;
try {      
    dBuilder = dbFactory.newDocumentBuilder();
} catch (ParserConfigurationException e) {
    e.printStackTrace();
}

但是当检查代码的安全性时，我遇到了两个在线安​​全问题

dBuilder = dbFactory.newDocumentBuilder();，分别是

1.XML实体扩展注入（XML炸弹）

2.XML外部实体注入（XXE攻击）

经过一番研究，我添加了这一行 dbFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);

但现在执行此行时出现异常

javax.xml.parsers.ParserConfigurationException: http://javax.xml.XMLConstants/feature/secure-processing

谁能帮帮我？

Answer 1

您是否尝试过来自OWASP page 的以下sn-p？

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException; // catching unsupported features
...

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
try {
  // This is the PRIMARY defense. If DTDs (doctypes) are disallowed, almost all XML entity attacks are prevented
  // Xerces 2 only - http://xerces.apache.org/xerces2-j/features.html#disallow-doctype-decl
  String FEATURE = "http://apache.org/xml/features/disallow-doctype-decl";
  dbf.setFeature(FEATURE, true);

  // If you can't completely disable DTDs, then at least do the following:
  // Xerces 1 - http://xerces.apache.org/xerces-j/features.html#external-general-entities
  // Xerces 2 - http://xerces.apache.org/xerces2-j/features.html#external-general-entities
  FEATURE = "http://xml.org/sax/features/external-general-entities";
  dbf.setFeature(FEATURE, false);

  // Xerces 1 - http://xerces.apache.org/xerces-j/features.html#external-parameter-entities
  // Xerces 2 - http://xerces.apache.org/xerces2-j/features.html#external-parameter-entities
  FEATURE = "http://xml.org/sax/features/external-parameter-entities";
  dbf.setFeature(FEATURE, false);

  // and these as well, per Timothy Morgan's 2014 paper: "XML Schema, DTD, and Entity Attacks" (see reference below)
  dbf.setXIncludeAware(false);
  dbf.setExpandEntityReferences(false);

  // And, per Timothy Morgan: "If for some reason support for inline DOCTYPEs are a requirement, then 
  // ensure the entity settings are disabled (as shown above) and beware that SSRF attacks
  // (http://cwe.mitre.org/data/definitions/918.html) and denial 
  // of service attacks (such as billion laughs or decompression bombs via "jar:") are a risk."

  // remaining parser logic
  ...

    catch (ParserConfigurationException e) {
        // This should catch a failed setFeature feature
        logger.info("ParserConfigurationException was thrown. The feature '" +
                    FEATURE +
                    "' is probably not supported by your XML processor.");
        ...
    }
    catch (SAXException e) {
        // On Apache, this should be thrown when disallowing DOCTYPE
        logger.warning("A DOCTYPE was passed into the XML document");
        ...
    }
    catch (IOException e) {
        // XXE that points to a file that doesn't exist
        logger.error("IOException occurred, XXE may still possible: " + e.getMessage());
        ...
    }

Answer 2

字符串 jaxbContext = "com.fnf.dfbatch.jaxb";

    JAXBContext jc = null;
    Unmarshaller u = null;
    String FEATURE_GENERAL_ENTITIES = "http://xml.org/sax/features/external-general-entities";
    String FEATURE_PARAMETER_ENTITIES = "http://xml.org/sax/features/external-parameter-entities";
    try {
        jc = JAXBContext.newInstance(jaxbContext);
        u = jc.createUnmarshaller();
        /*jobsDef = (BatchJobs) u.unmarshal(DfBatchDriver.class
                .getClassLoader().getResourceAsStream(
                        DfJobManager.configFile));*/

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();          
        dbf.setFeature(FEATURE_GENERAL_ENTITIES, false);            
        dbf.setFeature(FEATURE_PARAMETER_ENTITIES, false);      
        dbf.setXIncludeAware(false);
        dbf.setExpandEntityReferences(false);
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document document = db.parse(DfBatchDriver.class
                .getClassLoader().getResourceAsStream(
                        DfJobManager.configFile));
        jobsDef = (BatchJobs) u.unmarshal(document);