[连载2]高端java课程-代码审计中常见漏洞的特征函数-xxe-补充篇（框架设计者的无奈）_java代码审计危险函数

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我在一个软件中发现了一个类XXEUtil，主要作用是阻止出现xxe漏洞，进行一个预防措施，这确实是一个好的方案。

奈何！这个方案有个重大的弱点，他不是类似spring框架的AOP编程的思想实现的切面编程，需要开发人员在实际使用xml的时候调用这个类中的方法。

我截取了这个类的代码如下：

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.stream.XMLInputFactory;
import javax.xml.transform.sax.SAXTransformerFactory;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.dom4j.io.SAXReader;
import org.jdom.input.SAXBuilder;
import org.xml.sax.XMLReader;
 
public class XXEUtil {
 
   private static final Log LOG = LogFactory.getLog(XXEUtil.class);
 
 
   public static void prevent(XMLReader reader) {
      if(reader != null) {
         try {
            reader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
         } catch (Exception var2) {
            LOG.warn(var2);
         }
 
      }
   }
 
   public static void prevent(XMLInputFactory factory) {
      if(factory != null) {
         try {
            factory.setProperty("javax.xml.stream.supportDTD", Boolean.valueOf(false));
            factory.setProperty("javax.xml.stream.isSupportingExternalEntities", Boolean.valueOf(false));
         } catch (Exception var2) {
            LOG.warn(var2);
         }
 
      }
   }
 
   public static void prevent(SAXReader reader) {
      if(reader != null) {
         try {
            reader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            reader.setFeature("http://xml.org/sax/features/external-general-entities", false);
            reader.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
         } catch (Exception var2) {
            LOG.warn(var2);
         }
 
      }
   }
 
   public static void prevent(SAXBuilder builder) {
      if(builder != null) {
         try {
            builder.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            builder.setFeature("http://xml.org/sax/features/external-general-entities", false);
            builder.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
         } catch (Exception var2) {
            LOG.warn(var2);
         }
 
      }
   }
 
   public static void prevent(SAXTransformerFactory sf) {
      if(sf != null) {
         try {
            sf.setAttribute("http://javax.xml.XMLConstants/property/accessExternalDTD", "");
            sf.setAttribute("http://javax.xml.XMLConstants/property/accessExternalStylesheet", "");
         } catch (Exception var2) {
            LOG.warn(var2);
         }
 
      }
   }
 
   public static void prevent(DocumentBuilderFactory dbf) {
      if(dbf != null) {
         try {
            dbf.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
         } catch (Exception var2) {
            LOG.warn(var2);
         }
 
      }
   }
 
}

而我在全部代码中搜索，发现仅有一处地方调用了这个类的prevent函数。

   public SXWFileParser(File file) {
      try {
         this.setFile(file);
         String ex = file.getAbsolutePath();
         this.redXArchive = new RedXArchive(ex);
         this.reader = XMLReaderFactory.createXMLReader("org.apache.xerces.parsers.SAXParser");
         this.reader.setFeature("http://xml.org/sax/features/validation", false);
         this.reader.setFeature("http://xml.org/sax/features/external-general-entities", false);
         this.reader.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
         this.reader.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
         this.reader.setFeature("http://xml.org/sax/features/namespaces", true);
         XXEUtil.prevent(this.reader);
         this.handle = new RedXWriterContentHandler();
         this.reader.setContentHandler(this.handle);
         this.reader.setEntityResolver(this.handle);
      } catch (Exception var3) {
         log.error(var3.getMessage(), var3);
      }
 
   }

[高端java课程]本章重点

1. 国人开发的东西往往都是各自为政
2. 好的政策真正实施起来可能面目全非
3. 越是你认为没问题的地方，也许越是可能发现问题
4. 框架设计者以为自己做的很好，能防止大部分问题出现，而往往疏忽大意，这正是机会！